DIS2023 is the 30th in the series of annual workshops on Deep-Inelastic Scattering (DIS) and Related Subjects. The conference covers a large spectrum of topics in high energy physics. A significant part of the program is devoted to the most recent results from large experiments at BNL, CERN, DESY, FNAL, JLab and KEK. Theoretical advances are included as well.
DIS2023 will take place March 27–31, 2023 at the Kellogg Hotel and Conference Center on the campus of Michigan State University, East Lansing, Michigan, USA.
The main conference web page is at https://web.pa.msu.edu/conf/DIS2023.
The SLACK channel is https://join.slack.com/t/dis23/shared_invite/zt-1s5vy13du-nN87MWGEEtyFYaC~Z25ODA
Centennial Room
Building on the achievements of the Large Hadron Collider (LHC) and the projected reach of its high-luminosity upgrade (HL-LHC), the work of the Energy Frontier during the Snowmass 2021 community exercise has focused on building the case for future explorations at and above the TeV scale and has explored possible scenarios beyond the HL-LHC. In this talk I will present highlights of the main physics studies that have motivated the vision of future explorations presented in the Snowmass 2021 Report of the Energy Frontier.
During the LHC RunII, both ATLAS and CMS experiments collected a large data set. Compared to the LHC RunI results, we have achieved much higher precision on measuring Higgs features like Yukawa couplings and the inclusive cross section. Meanwhile, we gained unprecedented high sensitivity to search for Higgs rare and exotic decays, and also for long-lived particles through Higgs portals. This talk will present the recent results about these topics.
Diffractive phenomena constitute a large fraction of interactions occurring in pp collisions at LHC. Because of their non-perturbative nature, the present understanding is still relatively poor and uncertain. One of the methods to study these processes is forward proton tagging. I will discuss the mechanism of the diffractive processes, recent results, and potential implications. The proton tagging method can be used for measurements of photon-induced processes, in particular, the photon–photon interactions. I will present the physics behind these processes, the experimental status and the lessons we can learn for the strong interactions and for the electroweak sector.
I will discuss new developments in the study of physics beyond the Standard Model, including motivations based on the observations of the existence of dark matter and dark sectors, neutrino masses, the baryon asymmetry of the Universe, the flavor structure of the Standard Model fermions, and others. I'll discuss many strategies to resolve the origin of these mysteries, including direct and indirect searches both at colliders and beyond.
"Particle production in the projectile hemisphere (forward region)
introduces a kinematic asymmetry where the light-cone momenta of
projectile partons are much greater than those of the partons in the
target. The natural description of such processes is in terms of
eikonal propagation of very energetic projectile partons through a
strong color field. This approach permits the resummation of the
Glauber-Mueller multiple scattering series in terms of
eikonal phases, i.e. path ordered Wilson lines.
I provide an overview of some elements of the theory and its
application to the phenomenology of particle production and
correlations in the forward region of p+p and p+A collisions, as
well as DIS, with a focus on small-x physics, strong color fields,
and saturation."
In recent years, increased attention has been devoted to the issue diversity, equity and inclusion (DEI) in societal engagements, in particular in the scientific disciplines. Many institutions have been making efforts—with various degrees of commitment and success—to improve DEI within the context of their institutional activities. During the recent particle physics prioritization exercise, aka Snowmass, we studied the lack of diversity in high energy physics and made recommendations for improvement. In this talk, I will review the work done in Snowmass on DEI and offer suggestions about what is needed, beyond the institutional efforts, to make impactful progress on DEI issues.
BRODY SQUARE
Thanks to the high center-of-mass energy of the LHC, millions of top quarks have been produced and recorded, allow us to study the top quark related observables with a high precision. Deviations between theory predictions and experimental measurements in the top quark sector might indicate the first hints for new physics. This presentation focuses on the recent measurements at ATLAS and CMS experiments, including an overview of measurements of top quark productions, top quark mass and properties, and searches for the rare decays.
Heavy ion collisions allow access to novel QCD and QED studies in a laboratory setting. Experimental collaborations actively pursue this opportunity at RHIC and the LHC, and this vibrant physics program continues to yield insights into the interactions and properties of excited nuclear matter. Precision measurements of the properties of quark-gluon plasma (QGP) and the strong electromagnetic fields produced in high energy heavy ion collisions are among recent research pursuits, together with mapping of the phase diagram of nuclear matter through beam energy scanning. This talk will present recent experimental highlights from heavy ion collision data on various QGP and QED probes. I will explore the open questions and what could be addressed with future data from the two existing colliders and the upcoming EIC.
In this talk I review the current state of precision QCD simulations for the LHC and beyond.
"PDFs play a key role across a broad range of areas of contemporary and future interest, and so the need for precision PDFs is only increasing. I will therefore review the current status of precision PDF determination, including advances on the experimental, methodological and theoretical fronts, as illustrated by examples from across the field. In the course of this I will focus on recent developments and ongoing challenges as well as progress in confronting these issues, from dataset tensions through to the inclusion of N3LO effects and theoretical uncertainties and other state of the art developments. Finally, I will consider future challenges and opportunities to further our knowledge of PDFs and in turn proton structure.
The Parton Distribution Functions(PDFs), as an essential ingredient of realistic cross section calculation in the framework of perturbative QCD, describe the x-dependent structure of hadron base on global analysis amount hard-scattering measurements. As a weakness, the PDFs from global analysis receive larger uncertainty when data is scarce. Starting from first principle operator definitions of PDFs, PDF-related quantities are computed in the framework of Lattice QCD, and they provide comparisons and supplements for PDF from global analysis. In this presentation, we will talk about the current status and future prospects of PDF global analysis with Lattice-QCD inputs.
Spin is a unique probe to unravel the internal structure and QCD dynamics of nucleons. Exploration of the 3D spin structure of the nucleons is based on the complementarity of lepton scattering processes and purely hadronic probes. Some of the main questions that physicists have been trying to address in spin experiments involving different interactions and probes are: How does the spin of the nucleon originate from its quark, anti-quark, and gluon constituents and their dynamics? What can transverse-spin phenomena teach us about the structure of the nucleon and properties of QCD? In my talk, I will give an overview of selected recent results and future opportunities from the experimental campaigns probing the spin structure of nucleons utilizing both lepton scattering processes and hadron-hadron interactions, like Jefferson Lab experiments with electron beam, COMPASS muon-beam and Drell-Yann program, as well as the RHIC-Spin program with pp collisions.
We report the results of a new global QCD analysis including deep-inelastic scattering (DIS) data off $^1$H, $^2$H, $^3$H, and $^3$He targets. Nuclear corrections are treated in terms of a nuclear convolution approach with off-shell bound nucleons. The off-shell corrections responsible for the modification of the structure functions (SFs) of bound nucleons are constrained in a global fit along with the proton parton distributions (PDFs) and the higher-twist (HT) terms. In particular, we investigate the proton-neutron difference for these corrections. We also discuss our predictions for the SF ratio $F_2^n/F_2^p$ and the corresponding PDF ratio $d/u$ in the proton, as well as their correlations with the underlying treatment of the HT terms and of the off-shell corrections.
References
arXiv:2211.09514 [hep-ph]
In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure of the nucleus, analogous to deep inelastic scattering. This talk presents a measurement of jet production in UPCs performed with the ATLAS detector using high-statistics 2018 Pb+Pb data. Events are selected using requirements on jet production, rapidity gaps, and forward neutron emission to identify photo-nuclear hard-scattering processes. The precision of these measurements is augmented by studies of nuclear break-up effects, allowing for detailed comparisons with theoretical models in phase-space regions where significant nuclear PDF modifications are expected but not strongly constrained by existing data.
Analyzing data from nuclear lepton Deep-Inelastic Scattering, Drell-Yan processes, and W and Z boson production, we show that factorizing nuclear structure into quasi-free nucleons and universally modified close-proximity Short Range Correlated (SRC) nucleon pairs allows us to fully describe the quark-gluon structure of nuclei down to very-low momentum fractions. This is the first combined extraction of the universal distribution of quarks and gluons inside SRC pairs, and the nucleus-specific fraction of nucleons in SRC pairs. The extracted SRC fractions are in good agreement with previous nuclear structure calculations and measurements. This extraction of nuclear structure information from quark-gluon distributions thus represents a significant development toward understanding the structure of nuclei in terms of their fundamental quark-gluon constituents. At the same time such obtained nuclear PDFs are in very good agreement with fits using conventional framework of global nuclear PDF analysis.
Motivated by the wide range of kinematics covered by current and planned DIS facilities, we revisit the formalism, practical implementation, and numerical impact of target mass corrections (TMCs) for DIS on nuclear targets. These corrections are especially crucial for EIC physics. Within the Operator Product Expansion (OPE) formalism, we extend the analysis from individual nucleon targets (p,n) to nuclear targets, and express these nuclear TMCs in terms of re-scaled (or averaged) kinematic variables. An important aspect is that we use only nuclear, and later partonic, degrees of freedom. Additionally, we show the connection between the OPE and the Parton Model formalisms. Our results provide a representation of nuclear TMCs that seem to be universal for all nuclear targets; this allows us to construct a (computationally efficient) single-parameter fit for all nuclear TMCs that is in good numerical agreement with the full TMC computation. Finally, we discuss in detail the qualitative and quantitative differences between nuclear TMCs built in the OPE and the parton model formalisms, and also give numerical predictions for current and future facilities.
We consider the extension of the MSHT20 PDFs to an approximate N$^3$LO order. We describe the parameterisation of the missing N$^3$LO contributions and the determination of the theoretical uncertainties and their interpretation. We examine the impact of further data sets and look at the stability of predicted cross sections.
Measurements of Deep Inelastic Scattering (DIS) provide a powerful tool to probe fundamental structure of protons and other nuclei. The DIS cross sections can be expressed in terms of structure functions which are conventionally constructed via parton distribution functions (PDFs) that obey the DGLAP evolution equations. However, it is also possible to formulate the DGLAP evolution directly in terms of measurable DIS structure functions thereby entirely sidestepping the need for introducing PDFs. We call this as the physical-basis approach. In a global analysis one would thereby directly parametrize the (observable) structure functions -- not the (unobservable) PDFs. Ideally, with data constraints at fixed $Q^2$, the initial condition for the evolution would be the same at each perturbative order (unlike for PDFs) and the approach thus provides a more clean test of the QCD dynamics.
In the initial work reported here we first study a physical basis consisting of the structure functions $F_2$ and $F_{\rm L}$ in the fixed-flavour number scheme to the leading non-zero order in $\alpha_s$. We show how to express the quark singlet and gluon PDFs in terms of $F_2$ and $F_{\rm L}$ directly in momentum space which then leads to the DGLAP evolution of the structure functions $F_2$ and $F_{\rm L}$. In the second step we expand the physical basis to include six independent structure functions which allows for a consistent global analysis, and illustrate how to express e.g. the Drell-Yan cross sections at the LHC directly in terms of measurable DIS structure functions. The steps towards the NLO accuracy and variable-flavour-number scheme are outlined.
Parton distribution functions (PDFs) are most commonly determined by parameterizing them at some input scale Q_0 and then evolved to the desired scale Q through the DGLAP evolution equations. Extensions of the DGLAP equations have been proposed to account not only for the splitting of partons but also including non-linear 1/Q^n terms from the recombination of partons which slows down the pace of DGLAP evolution at small x. At sufficiently low Q the non-linear terms will eventually become the dominant ones and one enters the so-called saturation regime. In the work reported here, we have implemented a model for the leading 1/Q corrections in the DGLAP evolution code HOPPET and coupled it with xFitter to perform new global PDF fits accounting for the effects of recombination.
In the parton branching (PB) approach, Collinear and TMD parton densities have been determined by fits to inclusive deep inelastic scattering (DIS) HERA data. This method allows one to simultaneously take into account soft-gluon emission and the transverse momentum recoils in the parton branchings along the QCD cascade. The latter leads to a natural determination of the TMD PDFs in a proton. A new development is the inclusion of data from other measurements in a wider kinematic range in order to constrain the TMD PDFs and gain sensitivity to intrinsic transverse momentum contributions. We present the results at NLO for global PB TMD fits using the same HERAI+II inclusive DIS, plus HERA jet, Tevatron and fixed target and LHC W/Z data. The global TMD densities are used in the cascade3 Montecarlo event generator to predict observables at different energies.
Small-x, Diffraction and Vector Mesons
Recently, a novel factorization scheme has been put forward in the context of DIS . This new approach allows to connect the moderate x regime where the partonic picture is manifest to the small x regime best described by strong classical fields. In this work, we explore quantum evolution of the associated 3D gluon distribution that encodes saturation effects. In this framework, we obtain a new evolution equation that reduces to the BK an d BFKL equations at small x and connects smoothly to DGLAP at moderate x. We argue that this equation automatically resums large collinear logs that are know to be related to numerical instabilities in the NLO BK equation.
References:
[1] Renaud Boussarie, Yacine Mehtar-Tani, JHEP 07 (2022) 080, arXiv: 2112.01412 [hep-ph]
[2] Renaud Boussarie, Yacine Mehtar-Tani, in preparation
We revisit the problem of small Bjorken-$x$ evolution of the gluon and flavor-singlet quark helicity distributions in the shock wave (s-channel) formalism. Earlier works on the subject in the same framework resulted in an evolution equation for the gluon field-strength $F^{12}$ and quark “axial current” $\bar{\psi} \gamma^+ \gamma^5 \psi$ operators in the double-logarithmic approximation summing powers of $\alpha_s \log^2 (1/x)$. In this work, we observe that an important mixing of the above operators with another gluon operator, $\overleftarrow{D}^i D^i$, was missing in the previous works. This operator has the physical meaning of sub-eikonal (covariant) phase: its contribution to helicity evolution is shown to be proportional to another sub-eikonal operator, $D^i - \overleftarrrow{D}^i$, which is related to the Jaffe-Manohar polarized gluon distribution. In this work, we include this new operator into small-$x$ helicity evolution, and construct novel evolution equations mixing all three operators ($D^i - \overleftarrrow{D}^i$, $F^{12}$, $\bar{\psi} \gamma^+ \gamma^5 \psi$), generalizing previous results. We also construct closed double-logarithmic evolution equations in the large-$N_c$ and large-$N_c \& N_f$ limits, with $N_c$ and $N_f$ the numbers of quark colors and flavors, respectively. Solving the large-$N_c$ equation numerically we obtain the small-$x$ asymptotic of the quark and gluon helicity distributions $\Delta \Sigma$ and $\Delta G$, along with the $g_1$ structure function, which are in complete agreement with earlier works by Bartels, Ermolaev, and Ryskin.
We revisit the problem of the small Bjorken-$x$ asymptotics of the quark and gluon orbital angular momentum (OAM) distributions in the proton utilizing the revised formalism for small-$x$ helicity evolution derived recently in \footnote{F. Cougoulic, Y. V. Kovchegov, A. Tarasov, and Y. Tawabutr, Journal of High Energy Physics 2022,
10.1007/jhep07(2022)095 (2022).}. We relate the quark and gluon OAM distributions at small $x$ to the polarized dipole amplitudes and their (first) impact-parameter moments. To obtain the $x$-dependence of the OAM distributions, we derive novel small-$x$ evolution equations for the impact-parameter moments of the polarized dipole amplitudes in the double-logarithmic approximation (summing powers of $\alpha_s \ln^2(1/x)$ with $\alpha_s$ the strong coupling constant). We solve these evolution equations numerically and extract the large-$N_c$, small-$x$ asymptotics of the quark and gluon OAM distributions, which we determine to be
\begin{align}
L_{q+\bar{q}}(x, Q^2) \sim L_{G}(x,Q^2) \sim \Delta \Sigma(x, Q^2) \sim \Delta G(x,Q^2) \sim \left(\frac{1}{x}\right)^{3.66 \, \sqrt{\frac{\alpha_s N_c}{2\pi}}},
\end{align}
in agreement with \footnote{R. Boussarie, Y. Hatta, and F. Yuan, Physics Letters B 797, 134817 (2019).} within the precision of our numerical evaluation (here $N_c$ is the number of quark colors). We also investigate the ratios of the quark and gluon OAM distributions to their helicity distribution counterparts in the small-$x$ region.
When parton momentum faction $x$ of hadron becomes small, an enhancement from small-$x$ logarithms shows up, and eventually, we enter into a partonic saturation region. A consistent treatment of the small-$x$ logarithms requires an all-order resummation which can be achieved with the BFKL formalism. However, a boundary to delineate the small-$x$ resummation region from saturation one is ambiguous. In this study, we take a $x$-dependent DIS scale motivated by the saturation model in a global analysis, which improves the QCD description of the HERA DIS data. In parallel, we also explore the BFKL-improved DGLAP evolution, which achieves a similar $\chi^2$ for the same data set. We compare various impacts of these two methods on the parton distributions and emphasize the phenomenological implications on the Foward Physics Facility.
A crucial ingredient in all calculations in the Color Glass Condensate framework is the non-perturbative input to the perturbative small-$x$ evolution equation such as the Balitsky-Kovchegov (BK) equation. Due to the non-perturbative nature, it has to be determined from experimental data, most naturally from total DIS cross section measurements.
So far it has not been possible in leading order calculations to simultaneously describe the total and heavy quark production data from HERA without introducing additional quark flavor dependent parameters. This has been a major source of uncertainty in the studies of gluon saturation in the CGC framework.
In this work we predict heavy quark production cross sections in Deep Inelastic Scattering at high energy by applying the CGC effective theory. We demonstrate that when the calculation is performed consistently at next-to-leading order accuracy with massive quarks it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both light and heavy quark production data at small $x$. We furthermore show how the heavy quark cross section data provides additional strong constraints on the extracted non-perturbative initial condition for the small-$x$ evolution equations.
Reference:
H. Hänninen, H. Mäntysaari, R. Paatelainen, J. Penttala, arXiv:2211.03504 [hep-ph]
We study the single-inclusive particle production from proton-nucleus collisions in the dilute-dense framework of the color glass condensate (CGC) at next-to-leading order (NLO) accuracy. In this regime, the cross section factorizes into hard impact factors and dipole-target scattering amplitude describing the eikonal interaction of the partons in the target color field. We combine, for the first time, the NLO impact factors with the dipole amplitude evolved consistently using the next-to-leading order Balitsky-Kovchegov (BK) equation. Preliminary results in the quark-quark ($q\to q$) channel show that it is crucial to include all ingredients consistently at NLO accuracy in order to get a nuclear modification factor that is qualitatively compatible with the LHCb data. In particular, the NLO evolution coupled to leading order impact factor is shown to produce a large Cronin peak that is not visible in the LHC data. Further results in the $g\to g$, $q\to g$ and $g\to q$ channels are similar and will also be discussed, among with the importance of a proper choice of running coupling prescription.
Using the CGC effective theory together with the hybrid factorisation, we study forward photon+jet production in proton-nucleus collisions beyond leading order. We first compute the "real" next-to-leading order (NLO) corrections, i.e. the radiative corrections associated with a three-parton final state, out of which only two are being measured. Then we move to the "virtual" NLO corrections to dijet production, in which a gluon loop is included as a part of the amplitude, before or after the measurement. Each of these loop diagrams diverges, and we explain our treatment in order to obtain finite expression for the cross section. We explicitly work out the interesting limits where the unmeasured gluon is either a soft, or the product of a collinear splitting. We find the expected results in both limits: the B-JIMWLK evolution of the leading-order dijet cross-section in the first case (soft gluon) and, respectively, the DGLAP evolution of the initial and final states in the second case (collinear splitting).
One very promising observable to study gluon saturation effects at high energy is photon+jet production at forward rapidity in proton-nucleus collisions. Since the produced photon does not rescatter on the target, this observable provides a clean environment to study the interaction of the quark probe with the dense target.
In this talk, we will present the results for the photon-quark production cross-section (as a proxy for photon+jet) at next-to-eikonal accuracy taking into account finite-width target effects, dynamics of the target and the interaction with the subleading components of the background field. Moreover, we will also discuss the link between the high-energy Color Glass Condensate (CGC) formalism and the TMD factorization for this specific process. We will argue that next-to-eikonal corrections change the pattern of photon-jet correlations.
During the last ten years, a key problem in our understanding of particle production at small $x$ has been the fact that single inclusive particle spectra computed at NLO in pA collisions at forward rapidities using the hybrid model become negative at large transverse momenta. Different solutions have been proposed in the literature in the last years, including Sudakov and threshold resummation and sophisticated scale choices. Here we re-examine the negativity problem that is the result of an oversubtraction of logarithmic contributions. We show that the proper framework for resummation is not the collinear factorization as has been assumed heretofore, but rather TMD factorization. We find that all the logarithmically enhanced contributions can be resummed into perturbative evolution of transverse momentum dependent parton densities and fragmentation functions, allowing for a transparent physical interpretation. The resulting cross section is positive as it should be.
Electroweak Physics and Beyond the Standard Model
A search for off-shell production of the Higgs boson using 139 fb−1 of 𝑝𝑝 collision data at √𝑠 = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. The observable signature is a pair of on-shell 𝑍 bosons, with contributions both from the virtual Higgs boson and interference with other processes, and the two decay final states, 𝑍 𝑍 → 4ℓ and 𝑍 𝑍 → 2ℓ2𝜈 with ℓ = 𝑒 or 𝜇. The background-only hypothesis is rejected with an observed (expected) significance of 3.2 (2.4) 𝜎, which marks the experimental evidence of off-shell Higgs production. The observed (expected) upper limit on the signal strength, defined as the event yield normalised to the Standard Model prediction is 2.3 (2.4) at a 95% confidence level, which restricts the total width of the Higgs boson to be less than 9.7 (10.2) MeV at the same confidence level. Besides, the off-shell Higgs (220 GeV < mH < 2000 GeV) provides a pivotal window to search for BSM hints. The corresponding EFT interpretations for Higgs-gluon and Higgs-top quark interactions are also provided.
Combining measurements of many production and decay channels of the observed Higgs boson allows for the highest possible measurement precision for the properties of the Higgs boson and its interactions. These combined measurements are interpreted in various ways; specific scenarios of physics beyond the Standard Model are tested, as well as a generic extension in the framework of the Standard Model Effective Field Theory. The latest highlight results of these measurements and their interpretations performed by the ATLAS Collaboration will be discussed.
The discovery of the Higgs boson with the mass of 125 GeV confirmed the mass generation mechanism via spontaneous electroweak symmetry breaking and completed the particle content predicted by the Standard Model. Even though this model is well established and consistent with many experimental measurements, it is not capable of solely explaining some observations. Many extensions of the Standard Model introduce additional scalar fields to account for the electroweak symmetry breaking and thereby extra Higgs-like bosons, which can be either neutral or charged. This talk presents recent searches for additional Higgs bosons, as well as decays of the 125 GeV Higgs boson to new light scalar particles, using LHC collision data at 13 TeV collected by the ATLAS experiment in Run 2.
The Standard Model predicts several rare Higgs boson decay channels, among which are the decays to a Z boson and a photon, to a low-mass lepton pair and a photon, and to a meson and photon. The observation of some of these decays could open the possibility of studying the CP and coupling properties of the Higgs boson in a complementary way to other analyses. In addition, lepton-flavor-violating decays of the observed Higgs boson are searched for, where on observation would be a clear sign of physics effects beyond the Standard Model. Several results for decays based on pp collision data collected at 13 TeV will be presented.
With the large data set collected during Run 2 of the LHC, it is possible to measure precise Higgs Yukawa couplings and go beyond inclusive Higgs boson cross section measurements. Simplified template cross sections (STXS), which make use of several variables to divide up the phase space of the different Higgs boson production modes, and differential cross sections can be measured. The STXS binning is designed to be particularly sensitive to possible BSM effects. This talk will discuss the latest measurements from the CMS experiment in the H->tautau and H->bb decay channels.
Testing the Yukawa couplings of the Higgs boson to quarks and leptons is important to understand the origin of fermion masses. The talk presents several measurements in Higgs boson decays to two bottom quarks or two tau leptons, searches for Higgs boson decays to two charm quarks or two muons, as well as direct constraints of the charm-Yukawa coupling. The production of Higgs bosons in association with top quarks will also be discussed. These analyses are based on pp collision data collected at 13 TeV.
With the full Run 2 pp collision dataset collected at 13 TeV, very detailed measurements of Higgs boson properties can be performed using its decays into bosons. This talk presents measurements of Higgs boson properties using decays into bosons, including production mode cross sections and simplified template cross sections, as well as their interpretations.
Studies of the CP properties of the Higgs boson in various production modes and decay channels are presented. Limits on the mixing of CP-even and CP-odd Higgs states are set by exploiting the properties of diverse final states.
QCD with Heavy Flavours and Hadronic Final States
The production of jets and prompt isolated photons at hadron colliders provides stringent tests of perturbative QCD. We present the latest measurements using proton-proton collision data collected by the ATLAS experiment at √s =13 TeV. Prompt inclusive photon production is measured for two distinct photon isolation cones, R=0.2 and 0.4, as well as for their ratio. The measurement is sensitive to gluon parton density distribution. We will discuss the measurement of new event-shape jet observables defined in terms of reference geometries with cylindrical and circular symmetries using the energy mover's distance. In addition, we present the measurements of variables probing the properties of the multijet energy flow which are used to determine the strong coupling constant. The measurements are compared to state-of-the-art NLO and NNLO predictions.
Photoproduction is an important mode for production of jets and electro-weak particles at lepton--lepton and lepton--hadron colliders and allow for interesting studies of exclusive production at hadron--hadron colliders. In this talk, I will review recent efforts of extending the Sherpa event generator to include calculation of photoproduction for electron and proton beams, including the simulation of underlying events. The framework is validated using data of jet production at the HERA and LEP experiments and lepton production at the LHC. I will then discuss the advances towards achieving matched NLO accuracy and fully capturing the dynamics of inclusive and exclusive photoproduction at the different colliders.
The efficiency of non-local subtraction methods such as qT-subtraction or jettiness subtraction is affected by the size of the power corrections below the slicing cutoff used in the calculation. In this talk I will discuss the scaling of the power corrections for different classes of observables, focussing in particular on transverse observables, which do not depend on the rapidity of QCD radiation.
The production of W/Z bosons in association with heavy flavor jets or hadrons at the LHC is sensitive to the flavor content of the proton and provides an important test of perturbative QCD. We present the production of Z bosons in association with b-tagged large radius jets. The result highlights issues with modelling of additional hadronic activity and provides distinction between flavor-number schemes used in theoretical predictions. Moreover, the production of W boson in association with D+ and D*+ mesons will be discussed. This precision measurement provides information about the strange content of the proton. Measurements are compared to the state-of-the art NLO theoretical calculations.
In this talk, we plan to discuss recent results on third-order (N3LO) perturbative QCD corrections to observables in massive gauge boson production at the LHC. We describe how existing NNLO calculations for vector-boson-plus-jet processes can be utilized to obtain fully differential N3LO predictions for fiducial cross sections in leptonic final states, using the qT subtraction method. The combination of fixed order predictions with N3LL transverse momentum resummation is outlined.
The production of single top quarks as well as top-quark pairs in association with electroweak gauge bosons is presented together with the measurement of production asymmetries in ttbar and associated ttbar production. Using the data set collected during run 2 of the LHC (2015-2018, 139/fb of pp collisions at 13 TeV), the ATLAS experiment has observed ttX production, with X=gamma,Z and single top quark production with X=gamma,Z,W. In this contribution, inclusive as well as differential cross-section measurements are presented in a multitude of production processes. This includes the observation of the rare production of a single top quark together with a photon. The charge asymmetry in top-quark pair production is a subtle NLO effect in QCD that was experimentally confirmed at the Tevatron, in the form of a forward-backward asymmetry. ATLAS has observed significant evidence for this SM effect in the challenging LHC environment, combining the l+jets and di-lepton channels, and has measured the complementary energy asymmetry. The results are interpreted in terms of bounds on the Wilson coefficients of the SMEFT. Two additional measurements in rare associated production processes are presented for the rapidity charge asymmetry in ttgamma production and the lepton asymmetry in ttW production. Both measurements are statistically limited and have excellent prospects in future high-luminosity runs of the LHC.
We review the GENEVA Monte-Carlo framework, that combines three theoretical tools used for QCD precise prediction into a single structure.
It gives fully differential fixed-order calculations up to NNLO via $N$-jettiness subtraction, which are then combined with higher-order resummation in the $0$-jettiness resolution variable. This resummation is carried out to NNLL', matched to the appropriate fixed-order prediction. The resulting parton-level events are further combined with parton showering provided by PYTHIA8 and also other showers, giving a direct interface to hadronization and MPI simulations.
GENEVA consistently improves perturbative accuracy away from the fixed-order regions, providing event-by-event a systematic estimate of the theoretical perturbative uncertainties.
It this talk we highlight its main features, discussing some new improvements involving both color singlet productions, as well as for the production of final states with heavy coloured partons and jets.
The associated production of a Higgs boson with a top-antitop quark pair is a crucial process at the LHC since it allows for a direct measurement of the top-quark Yukawa coupling.
In this talk we present our recent computation of the NNLO QCD corrections to ttH production within qT-subtraction, with an emphasis on the steps needed to apply this formalism to this process and on possible further applications.
We present theoretical calculations of total cross sections and top-quark transverse-momentum and rapidity distributions in the associated production of a top-antitop pair with a photon ($t{\bar t}\gamma$ production). We include complete QCD and electroweak corrections at NLO as well as soft-gluon corrections at approximate NNLO (aNNLO). The aNNLO corrections are very significant, they decrease theoretical uncertainties, and they are needed for better comparison with data from the LHC.
Spin and 3D Structure
We will present results on Spin Density Matrix Elements (SDMEs) measured in hard exclusive muoproduction of $\rho ^0$, $\omega $ and $\phi$ mesons on the proton at COMPASS using 160 GeV/$c$ polarised $\mu ^{+}$ and $\mu^{-}$ beams scattering off a liquid hydrogen target. The measurements cover the range 5 GeV/$c^2$ $< W <$ 17 GeV/$c^2$, 1.0 (GeV/$c$)$^2$ $< Q^2 <$ 10.0 (GeV/$c$)$^2$ and 0.01 (GeV/$c$)$^2$ $< p_T^2 <$ 0.5 (GeV/$c$)$^2$. Here, $Q^2$ denotes the virtuality of exchanged photon, $W$ the mass of final hadronic system and $p_T$ the transverse momentum of the vector meson with respect to the virtual-photon direction. The measured non-zero SDMEs for transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($\gamma _{T} \rightarrow V_{L}$) indicate a violation of $s$-channel helicity conservation. Additionally, for $\rho ^0$ and $\phi$ production we observe a dominant contribution of natural-parity-exchange (NPE) transitions and a small contribution of unnatural-parity-exchange (UPE) transitions. On the contrary the UPE contribution for $\omega $ production is significant and it decreases with increasing $W$, being still non-negligible at the largest $W$ values accessible at COMPASS. The results provide an important input for modelling Generalised Parton Distribution (GPDs). In particular, they may allow to evaluate in a model-dependent way the role of parton helicity-flip GPDs ("transversity GPDs") in exclusive vector meson production.
We study the small-x evolution equation for the gluon generalized parton distribution (GPD) Eg of the nucleon. It is shown that Eg at vanishing skewness exhibits the Regge behavior identical to the BFKL Pomeron, despite its association with nucleon helicity-flip processes. We also consider the effect of gluon saturation and demonstrate that Eg gets saturated in the same way as its helicity-nonflip counterpart Hg. Our result has a direct impact on the modeling of Eg as well as the small-x contribution to nucleon spin sum rules.
In this talk we present our theoretical studies of heavy quarkonia pair electro- and photoproduction in the collinear factorization framework. We focus on $J/\psi\ \eta_c$ pair production, and discuss the relation of different observables to generalized parton distributions (GPDs) of gluons. The unpolarized cross-section is dominated by contributions of transversely polarized $J/\psi$ mesons, which in the leading twist is controlled by the unpolarized gluon GPDs $H_g, E_g$. We also discuss other observables which might be sensitive to other GPDs of gluons. We provide numerical estimates in the kinematics of the future Electron Ion Collider.
We present a further step toward a global extraction of gluon generalized parton distributions (GPDs). In our previous work we performed the first global analysis of quark GPDs by including lattice quantum chromodynamics (QCD) calculations, global fitted forward parton distribution functions (PDFs), form factors (FFs), and Deeply Virtual Compton Scattering (DVCS) measurements from JLab and Hadron-Electron Ring Accelerator (HERA) to constrain two quark flavors with leading order QCD evolution. There, the inclusion of DVCS did not probe gluon structure at leading order, as the gluon GPDs only enter through evolution. Here, we include HERA measurements of Deeply Virtual Meson Production (DVMP) in order to study gluon GPDs at non-zero skewness using the same moment parameterization ansatz and within the same global fit with lattice QCD calculations and experimental measurements. We concentrate our study on the production of mesons comprised of heavy quarks such as $J/\psi$ in order to limit quark contributions and thus allow for greater constraint upon the gluons GPDs.
We will present COMPASS measurements of Deeply Virtual Compton Scattering and of exclusive pi0 production on the proton using 160 GeV polarized mu+ and mu- beams at the CERN SPS impinging on a 2.5m long liquid hydrogen target. The target was surrounded by a barrel-shaped time-of-flight system to detect the recoiling target protons. The scattered muons and the produced real photons were detected by the COMPASS spectrometer, which was supplemented by an additional electromagnetic calorimeter for the detection of large-angle photons.
We will show the charge-spin average DVCS cross section differential in the squared four-momentum transfer to the proton, which is mainly sensitive to the GPD H and is expected to be sensitive to the transverse extension of partons in the proton. COMPASS allows for a first access to the Bjorken-x domain of sea quarks.
Exclusive pi0 production is the main source of background for the DVCS measurement, while it provides complementary information for the parametrization of GPDs. We will report on results for the exclusive pi0 production cross section and its dependence on the squared four-momentum transfer and on the azimuthal angle between the scattering plane and the pi0 production plane. This reaction is aiming to constrain GPDs, in particular chiral-odd (“transversity”) GPDs.
We calculate the one-loop quark box diagrams relevant to polarized and unpolarized Deep Virtual Compton Scattering by introducing an off-forward momentum $l^\mu$ as an infrared regulator. Such a regularization enables us to unravel the poles $1/l^2$ related to the chiral anomaly in the polarized case and the trace anomaly in the unpolarized case. We interpret our results in terms of the relevant Generalized Parton Distributions, and discuss the implications of the poles on the QCD factorization for Compton amplitudes.
Traditionally, lattice QCD computations of GPDs have been carried out in a frame, where the transferred momentum is symmetrically distributed between the incoming and outgoing hadrons. However, such frames are inconvenient for lattice QCD calculations since each value of the momentum transfer requires a separate calculation, increasing the computational cost. In a recent work (arXiv:2209.05373), we lay the foundation for more effective calculations of GPDs applicable for any frame, with freedom in the transferred momentum distribution. An important aspect of the approach is the Lorentz covariant parameterization of the matrix elements in terms of Lorentz-invariant amplitudes, which allows one to relate matrix elements in different frames. We demonstrate the efficacy of the formalism through numerical calculations using one ensemble of $N_f=2+1+1$ twisted mass fermions with a clover improvement. The value of the light-quark masses lead to a pion mass of about 260 MeV. Concentrating on the proton and zero skewness, we extract the invariant amplitudes from matrix element calculations in both the symmetric and asymmetric frame, and obtain results for the twist-2 light-cone GPDs for unpolarized quarks, $H$ and $E$.
We present a lattice QCD determination of the nucleon generalized parton distributions (GPDs) from an analysis of the quasi-GPD matrix element within the leading-twist framework. We preform our study on a Nf=2+1+1 twisted mass fermions ensemble with a clover improvement. The faster and more effective lattice QCD calculations of GPDs using the asymmetric frames was applied so that we can achieve multiple momentum transfers $t$ with reduced computational cost. The quasi-GPD matrix elements are renormalized using the ratio scheme and analyzed using the leading-twist Mellin operator product expansion (OPE) at the next-to-leading order. We find a robust result for the first non-vanishing Mellin moments <x> and <x^2> as a function of $t$.
Both deeply-virtual and photoproduction of mesons offer promising access
to generalized parton distributions and complementary description of different kinematical regions. The higher-order contributions offer stabilizing effect with respect to the dependence on renormalization scales, while higher-twist effects have been identified as especially important in the case of the production of pseudo-scalar mesons. This was confirmed by recent evaluation of the complete twist-3 contribution to $\pi$ and $\eta$ ($\eta'$) production and its confrontation with experimental data.
Future Experiments
The international ePIC collaboration has formed to design and construct the general purpose detector to be ready at the beginning of operation of the Electron-Ion Collider. ePIC will be located at the IP6 interaction region of the RHIC/EIC accelerator. By measuring inclusive and semi-inclusive DIS (where the target is shattered) and exclusive processes (where the target is left intact) in electron-ion collisions with high-luminosity over a large range of parton momentum and spatial resolution, profound mysteries in the fundamental structure of visible matter can be explored with unprecedented precision. The planned measurements demand challenging detector requirements.
The ePIC science and detector will be described and the status and future path summarized.
EPIC is a general-purpose detector designed to deliver the full physics program of the Electron-Ion Collider (EIC). Particle identification (PID) at the EIC is an essential asset as well as a challenge: the PID systems have to provide excellent separation of pions, kaons, and protons over a large phase space with significant pion/electron suppression. EPIC addresses the physics requirements by utilising multiple state-of-the-art particle identification technologies.
This talk presents the EPIC detector PID subsystems, with particular emphasis on the high-momentum particle-identification systems based on DIRC and RICH techniques exploiting Cherenkov light emission by charged particles. R&D activities are under way to evaluate the use of SiPMs as photosensors for the RICH detectors, to explore the capabilities of the novel LAPPD detectors and to evaluate the compatibility of commercial MCP-TMP with the magnetic field conditions of the experiment. The projected performance of the PID detector system studied via detailed Geant4 simulations will also be discussed as well as possible future upgrades.
Excellent particle identification (PID) is one of the key requirements for the central detector of the Electron-Ion collider (EIC). Identification of the hadrons in the final state is important to study how different quark flavors contribute to nucleon properties. A detector with a radial size of only 7-8 cm, which uses the principle of Detection of Internally Reflected Cherenkov light (DIRC), is a very attractive solution to meet these requirements. The high-performance DIRC (hpDIRC) was developed to extend the momentum coverage well beyond the state-of-the-art 3 standard deviations or more separation of $\pi/K$ up to at least 6 GeV/$c$ in the polar angle range $30^{\circ}-145^{\circ}$. Additionally it is expected to provide separation power for p/K up to 10 GeV/$c$, and low momentum e/$\pi$. The key element of the hpDIRC detector is a custom-made 3-layer compound lens used to focus Cherenkov photons produced by charged tracks to small pixel-size photo-sensors leading to measure the position and time of the photons with great precision and finally identify the charged particle. hpDIRC detector was selected for the baseline design of the central region of the ePIC detector. The advanced R&D program for the hpDIRC is focused on physics based simulation studies of performance, including magnetic fields and backgrounds. Hardware R$\&$D is focused on prototype program at newly assembled Cosmic Ray Telescope (CRT) at Stony Brook University (SBU) and BaBar bars validation at JLab. In this talk an overview of the hpDIRC detector development will be presented.
The physics program at the High Luminosity LHC (HL-LHC) calls for a precision in the luminosity measurement of 1%. A larger uncertainty would represent the dominant systematic error in several precision measurements, including in the Higgs sector. To fulfil this requirement in an environment characterized by up to 140 simultaneous interactions per bunch crossing (200 in the ultimate scenario), ATLAS will rely on multiple, complementary luminosity detectors, covering the full range of HL-LHC beam conditions from the low-luminosity, low-pileup regime of the van der Meer (vdM) calibrations to the high-luminosity environment typical of physics running.
The ATLAS luminometer coverage at HL-LHC will extensively build on the experience obtained in the current third running period of the LHC. The interplay of several luminometers, based on different technologies is essential for a high-precision luminosity measurement. The HL-LHC successor of LUCID-2 - the reference ATLAS luminometer since the beginning of the second running period of the LHC - is LUCID-3. Both devices are based on small acceptance photomultiplier tubes (PMTs) whose quartz entrance window serve as a Cerenkov radiator. Two different prototypes for LUCID-3 are installed in the ATLAS cavern and have been taking data since the beginning of the 2022 LHC run. Diamond- and silicon-pad technology are used in, respectively, the BCM’ detector, inspired by the present ATLAS Beam Conditions Monitor, and the BMA (“Beam Monitor for ATLAS”). The latter is optimized for a highly linear response in the intermediate- and high-luminosity regimes, and had an early prototype installed and recording its first data in 2022. The Pixel-cluster-counting (PCC) technique is exploited by two very different luminometers: the Si- based pixel-luminosity ring (PLR), integrated in the very forward section of the upgraded inner tracker (ITk), and the HGTD (High Granularity Timing Detector), based on LGAD technology. The full ITk will also be used for track- and PCC-based offline-luminosity measurements. The upgraded ATLAS calorimeters will provide luminosity measurement through the LAr-gap current in the end-cap and forward electromagnetic calorimeters, and the PMT currents of the TILE hadronic calorimeters, both of which play an essential role in reducing systematic biases in luminosity measurements.
The presentation will outline of the ATLAS strategy for luminosity determination at the HL-LHC, discuss the plans for the luminometer upgrades, the status of the existing prototypes and their first results.
The Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment, with steel as absorber and plastic scintillators as active medium. The High-Luminosity phase of LHC, delivering five times the LHC nominal instantaneous luminosity, is expected to begin in 2029. TileCal will require new electronics to meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will be replaced during the shutdown of 2026-2028. PMT signals from every TileCal cell will be digitized and sent directly to the back-end electronics, where the signals are reconstructed, stored, and sent to the first level of trigger at a rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. The modular front-end electronics feature radiation-tolerant commercial off-the-shelf components and redundant design to minimise single points of failure. The timing, control and communication interface with the off-detector electronics is implemented with modern Field Programmable Gate Arrays (FPGAs) and high speed fibre optic links running up to 9.6 Gb/s. The TileCal upgrade program has included extensive R&D and test beam studies. A Demonstrator module with reverse compatibility with the existing system was inserted in ATLAS in August 2019 for testing in actual detector conditions. The ongoing developments for on- and off-detector systems, together with expected performance characteristics and results of test-beam campaigns with the electronics prototypes will be discussed.
The possibility of a joint interaction region and detector which could study ep/eA and pp/pA/AA at the HL-LHC was presented in [1]. Here we show the most recent developments on the design of such novel interaction region where, in ep/eA mode, one hadron or nuclear beam must go through the region unscathed while in hh mode that beam must be focused to collide with the other hadron or nuclear beam. We also comment on the integration with the other HL-LHC interaction points and on the realisation of such interaction region at the FCC. We finally present a detector concept suitable to serve precision measurements both in eh and hh collisions.
[1] K.D. J. Andre et al., Eur. Phys. J. C 82 (2022) 1, 40, e-Print: 2201.02436 [hep-ex].
The Large Hadron-electron Collider and the Future Circular Collider in electron-hadron mode [1] will make possible the study of DIS in the TeV regime providing electron-proton (nucleus) collisions with per nucleon instantaneous luminosities around $10^{34}$ ($10^{33}$) cm$^{-2}$s$^{-1}$. Here we describe the current detector design for such experiments [1,2] and the key developments needed, included in the 2021 ECFA detector research and development roadmap [3], particularly concerning machine-detector interface and large acceptance tracking and calorimetry, and the technological choices to be taken in order to fulfil the demands of their physics programmes.
[1] LHeC Collaboration and FCC-he Study Group: P. Agostini et al., J. Phys. G 48 (2021) 11, 110501, e-Print: 2007.14491 [hep-ex].
[2] K.D. J. Andre et al., Eur. Phys. J. C 82 (2022) 1, 40, e-Print: 2201.02436 [hep-ex].
[3] ECFA Detector R&D Roadmap Process Group, report CERN-ESU-017, http://cds.cern.ch/record/2784893, 10.17181/CERN.XDPL.W2EX.
In the high-luminosity era of the Large Hadron Collider, the instantaneous luminosity is expected to reach unprecedented values, resulting in up to 200 proton-proton interactions in a typical bunch crossing. To cope with the resulting increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The innermost part of the ITk will consist of a pixel detector, with an active area of about 13 m2. To deal with the changing requirements in terms of radiation hardness, power dissipation and production yield, several silicon sensor technologies will be employed in the five barrel and endcap layers. Prototype modules assembled with RD53A readout chips have been built to evaluate their production rate. Irradiation campaigns were done to evaluate their thermal and electrical performance before and after irradiation. A new powering scheme – serial – will be employed in the ITk pixel detector, helping to reduce the material budget of the detector as well as power dissipation. This contribution presents the status of the ITk-pixel project focusing on the lessons learned and the biggest challenges towards production, from mechanics structures to sensors, and it will summarize the latest results on closest-to-real demonstrators built using module, electric and cooling services prototypes.
ATLAS-ITK Strip Collaboration
(the speaker to be selected by the ITk Speakers Committee after the contribution acceptance)
The inner detector of the present ATLAS experiment has been designed and developed to function in the environment of the present Large Hadron Collider (LHC). At the ATLAS Phase-II Upgrade, the particle densities and radiation levels will exceed current levels by a factor of ten. The instantaneous luminosity is expected to reach unprecedented values, resulting in up to 200 proton-proton interactions in a typical bunch crossing. The new detectors must be faster and they need to be more highly segmented. The sensors used also need to be far more resistant to radiation, and they require much greater power delivery to the front-end systems. At the same time, they cannot introduce excess material which could undermine tracking performance. For those reasons, the inner tracker of the ATLAS detector was redesigned and will be rebuilt completely.
The ATLAS Upgrade Inner Tracker (ITk) consists of several layers of silicon particle detectors. The innermost layers will be composed of silicon pixel sensors, and the outer layers will consist of silicon microstrip sensors. This contribution focuses on the strip region of the ITk. The central part of the strip tracker (barrel) will be composed of rectangular short (~ 2.5 cm) and long (~5 cm) strip sensors. The forward regions of the strip tracker (end-caps) consist of six disks per side, with trapezoidal shaped sensors of various lengths and strip pitches. After the completion of final design reviews in key areas, such as Sensors, Modules, Front-End electronics, and ASICs, a large scale prototyping program has been completed in all areas successfully. We present an overview of the Strip System and highlight the final design choices of sensors, module designs and ASICs. We will summarise results achieved during prototyping and the current status of pre-production and production on various detector components, with an emphasis on QA and QC procedures.
There has been significant discussion in the community regarding a future $\mu^+\mu^-$ collider. While such a facility is still decades away from realization, it is also understood that significant technological development and feasibility demonstrations are necessary at lower beam energies. Here we propose such a possibility coupled with a rich physics program. We propose a future Muon-Ion Collider that would serve as a natural extension to the EIC program currently planned in the 2030’s and 40’s. We envision this collider would be implemented as an upgrade to the EIC, with $\mu$ beam energies between 18 GeV and 200 GeV and a luminosity of $10^{33}$ cm$^{-2}$s$^{-1}$. In this presentation we discuss the challenges of generating $\mu$ beams that satisfy the design requirements of such a collider, and review some current efforts in the field to design such beams. We discuss the physics reach of a future muon-ion collider and identify opportunities for synergy between the nuclear and particle physics communities.
Funding acknowledgment: This material is based upon work supported by the National Science Foundation under Grant No. PHY 2012114, and the Center for Frontiers in Nuclear Science at Stony Brook University.
https://web.pa.msu.edu/conf/DIS2023/Mentoring.html
We present recent progress within the NNPDF analysis of parton distribution functions aimed to i) improve the accuracy of the determination by accounting for (approximate) N3LO corrections to the splitting functions and partonic matrix elements, ii) estimate the impact of missing higher order uncertainties within the NNLO global analysis, and iii) account for QED corrections and the impact of a photon PDF, as required for LHC calculations in the presence of electroweak corrections. We also study the interplay of these various developments, in particular that of MHOUs in the context of the N3LO NNPDF determination. We assess the impact of these theoretical developments for key processes at the LHC.
We provide a summary of recent developments on the MSHT parton distribution functions. This includes the addition of a variety of new data sets into the fit, and the potential impact of EIC data. The primary impact is seen on the details of the high-$x$ PDFs. We also consider the impact of procedural choices, and the effect of changes of PDFs on predicted cross sections.
We discuss recent developments in the global QCD analysis of parton distribution functions by CTEQ-TEA collaboration.
The question of the existence and possible magnitude of nonperturbative (often called "intrinsic") charm in the proton has long confounded attempts to cleanly isolate such a contribution in global analyses of high-energy experiments. In this talk, we show that the available (non)perturbative QCD theory and hadronic data have still not developed to a sufficient level to clearly resolve this problem. We highlight a number of challenging aspects that must be confronted in extracting nonperturbative charm in PDF fits, and in so doing, present an updated next-to-next-to-leading order CTEQ-TEA (CT) analysis of fitted charm, CT18 FC, which we also compare to recent studies. We outline the theory developments and future data needed to make progress on this subject.
We report about the impact of novel high-precision top-quark pair production 13 TeV measurements and other HF data from ATLAS and CMS on the CT18 global analysis of PDFs. We discuss features of a new top-quark data combination which complements the CT18 baseline. We discuss the impact on the gluon PDF and the extraction of the mass of the top quark in the pole mass approximation.
This abstract is suitable for a talk in both the WG1 and WG4 working groups.
We present the xFitter project which provides an open-source software framework for the determination of the proton's parton distribution functions and for the interpretation of the physics analyses in the context of Quantum Chromodynamics. The project has been used for a number of analyses performed by the LHC collaborations and theory community, which are summarised briefly. The xFitter program has been updated recently to a new version with new features and a more flexible development interface. Recent results obtained by the xFitter developers’ team are discussed as well.
A new measurement of inclusive jet cross sections in neutral current deep inelastic scattering using the ZEUS detector at the HERA collider is obtained. The data were taken at HERA 2 at a center of mass energy of 318 GeV and correspond to an integrated luminosity of 347 pb−1. Massless jets, reconstructed using the kT-algorithm in the Breit reference frame, are measured as a function of the squared momentum transfer Q2 and the transverse momentum of the jets in the Breit frame p_{T,Breit}. The measured jet cross sections are compared to previous measurements as well as NNLO QCD theory predictions. The measurement is used in a QCD analysis at NNLO accuracy to perform a simultaneous determination of parton distribution functions of the proton and the strong coupling constant. A significantly improved accuracy is observed compared to similar measurements of the strong coupling constant.
Recent measurements of jet cross sections in proton-proton collisions with the CMS experiment are presented. The measured jet cross sections are corrected for detector effects and compared with the predictions from perturbative QCD, and exploited to derive constraints on parton distribution functions and to mesure alpha_S.
SeaQuest has measured dimuon events from the interaction of 120 GeV proton beam on liquid hydrogen and deuterium targets with dimuon mass between 2 and 8 GeV. These dimuon events contain both the Drell-Yan process and the charmonium ($J/\psi$ and $\psi^\prime$) production. The first result of the Drell-Yan $(p+d)/2(p+p)$ cross section ratio, based on the analysis of a fraction of the collected data, has provided new information on the light sea quark asymmetry. Analysis of the entire data set to extract the $\bar{d}/\bar{u}$ ratio is currently underway, and the status of this analysis will be reported. Unlike the Drell-Yan process which probes the antiquark distributions in the nucleons, the charmonium production is sensitive to both quark and gluon distributions. The status of the charmonium analysis will also be discussed.
While the unpolarized valence quark ($d$ and $u$) distributions are well determined from DIS and $pp/p\bar{p}$ experiments, their sea quark counterparts, $\bar{d}$ and $\bar{u}$, are much less constrained, in particular, near the valence region.
Measurements of $W^+/W^-$ production ratio in $pp$ collider experiments, such as the STAR experiment at RHIC, are sensitive to the $\bar{d}/\bar{u}$ ratio at a large $Q^2$ set by the $W$ mass.
Presented in this talk are the latest updates of $W^+$ and $W^-$ cross-section ratio measurement via lepton-decay tagging, using the STAR $pp$ collision data at a center-of-mass energy of $\sqrt{s} = 510\,\mathrm{GeV}$ collected in 2017, corresponding to an integrated luminosity of $350\,\mathrm{pb^{-1}}$.
The measurements cover the mid $(|\eta|<1)$ and intermediate rapidities $(1 < \eta < 2)$, probing the $\bar{d}/\bar{u}$ ratio within the proton momentum fraction range of $0.06 < x < 0.4$.
Presented are the latest updates of the measurement of the azimuthal decorrelation angle and the transverse momentum imbalance between the leading jet and the scattered lepton in deep inelastic scattering with the ZEUS detector at HERA. During the HERA II data-taking period, electrons and positrons collided with protons with a center of mass energy of 318 GeV. The total integrated luminosity is 326 pb−1. The analysis is based on data with an exchanged photon virtuality, Q2, in the range of 10 GeV2 < Q2 < 350 GeV2 and inelasticity, y, in the range of 0.04 < y < 0.7. Events were selected where the scattered electron or positron had an energy Ee > 10 GeV and the jets had transverse momenta, p_{T,jet}, and pseudorapidities, eta_{jet}, of 2.5 GeV < p_{T,jet} < 30 GeV and −1.5 < eta_{jet} < 1.8, respectively. Normalized differential cross sections are presented as functions of p_{T,jet} , Q2 and jet multiplicity.
Correlations between charged particles provide important insight about the hadronization process. The analysis of the momentum difference between charged hadrons in pp, p-lead, and lead-lead collisions of various energies is performed in order to study the dynamics of hadron formation. The spectra of correlated hadron chains are explored and compared to the predictions based on the quantized fragmentation of a three dimensional QCD helix string. The measurement provides insight into the mismodelling of low transverse momentum production of charged particles observed in ee, pp and heavy ion collisions. If ready, the measurement of charged particle distributions using LHC data collected at 13.6 TeV of centre-of-mass energy will also be shown.
Small-x, Diffraction and Vector Mesons
The LHCb detector's forward geometry provides unprecedented kinematic
coverage at low Bjorken-x. LHCb's excellent momentum resolution,
vertex reconstruction, and particle identification enable precision
measurements at low transverse momentum and high rapidity in
proton-lead collisions, probing x as small as 10^-6. In this
contribution, we present recent studies of low-x physics using the
LHCb detector. These studies include charged hadron, neutral pion, and
D0 production in proton-lead collisions, as well as charmonium
production in ultraperipheral lead-lead collisions. Future prospects
and implications for the understanding of low-x nuclear PDFs and
parton saturation are also discussed.
The elastic scattering of protons at 13 TeV is measured in the range of the protons' transverse momenta allowing the access to the Coulomb-Nuclear-Interference region. The data were collected thanks to dedicated special LHC beta* = 2.5km optics. The total cross section as well as rho-parameter, the ratio of the real to imaginary part of the forward elastic scattering amplitude, are measured and compared to various models and to results from other experiments. The measurement of exclusive production of pion pairs at the LHC using 7 TeV data is also presented. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC.
This talk presents ATLAS recent measurements of distributions sensitive to Underlying event, the hadronic activity observed in relationship with the hard scattering in the event using the full ATLAS dataset at center-of-mass energy of 13 TeV. Measurement of charged-particle distributions as a function of Upsilon momentum and different Upsilon states will be discussed. The measurement benefits from the heavy-ion style approach to remove combinatorial and pileup backgrounds leading to increased sensitivity. In addition, charged-particle distributions measured in top-antitop events decaying leptonically will be shown. The measured distributions can constrain models of the color reconnection mechanism in Monte-Carlo generators.
Gluons are found to become increasingly dominant constituents of nuclear matter when being probed at higher energies or smaller Bjorken-$x$ values. This has led to the question of the ultimate fate of nuclear gluonic structure and its interaction with external probes at extreme density regimes when approaching the limit allowed by unitarity. In ultraperipheral collisions (UPCs) of relativistic heavy ions, the coherent heavy-flavor vector meson production via photon-nuclear interactions is of particular interest, since its cross section is directly sensitive to the nuclear gluon density. However, in experimental measurements, because each of the two nuclei in symmetric UPCs can serve both as a photon-emitter projectile and a target, this two-way ambiguity has prevented us from disentangling contributions involving high- and low-energy photon-nucleus interactions, thus limiting our capability of probing the extremely small-$x$ regime, where nonlinear QCD effects are expected to emerge.
In this talk, we will present a new measurement of coherent $\rm{J}/\psi$ photoproduction, where the two-way ambiguity is solved by implementing for the first time a forward neutron tagging technique in UPC PbPb collisions at 5.02 TeV. The coherent $\rm{J}/\psi$ photoproduction cross section will be presented as a function of the photon-Pb center-of-mass energy in UPCs up to about 400 GeV, corresponding to an extremely low x of $\sim{5\times10^{-5}}$. We will discuss the physics implications of this new result, as well as exciting opportunities in future LHC heavy ion runs.
Since 2011 a wide variety of measurements suggest the existence of strong collectivity in collisions of small systems such as proton-proton (pp) and proton-nucleus (pPb) with hydrodynamic models and gluon saturation in the initial state as two theory alternatives showing consistency with the observations. These results raise the question as to whether such phenomena may be present in even smaller systems. Just recently ATLAS, ALEPH, and ZEUS collaborations have extended the studies to photon-Pb, electron-electron (ee), and electron-proton (ep) systems respectively. This talk will summarize the latest CMS results on the study of long-range particle correlations extended to photon-proton and pomeron-Lead interactions using pPb collisions at 8.16 TeV. Such interactions provide unique initial conditions with event multiplicity lower than in pp and pPb systems but comparable with ee and ep systems.
We present a phenomenological analysis of events with two high transverse momentum jets separated by a large rapidity interval void of particle activity, also known as jet-gap-jet events. In the limit where the collision energy is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between partons within the Balitsky-Fadin-Kuraev-Lipatov limit of perturbative quantum chromodynamics (QCD). The BFKL pomeron exchange amplitudes, with resummation at the next-to-leading logarithmic approximation, have been embedded in the PYTHIA8 Monte Carlo event generator. Standard QCD dijet events are simulated at next-to-leading order in αss matched to parton showers with POWHEG+PYTHIA8. We compare our calculations to measurements by the CDF, D0, and CMS experiments at center-of-mass energies of 1.8, 7 and 13 TeV. The impact of the theoretical scales, the parton densities, final- and initial-state radiation effects, multiple parton interactions, and pT thresholds and multiplicities of the particles in the rapidity gap on the jet-gap-jet signature is studied in detail. With a strict gap definition (no particle allowed in the gap), the shapes of most distributions are well described except for the CMS azimuthal-angle distribution at 13 TeV. The survival probability is surprisingly well modelled by multiparton interactions in PYTHIA8.
In order to solve the proton spin problem, the small-$x$ asymptotics of the helicity parton distribution functions (hPDFs) need to be understood. New theory has been developed for the small-$x$ evolution of these hPDFs, able to extrapolate the small-$x$ behaviour of the quark and gluon hPDFs. At large $N_c \& N_f$, these evolution equations close and are amenable to numerical computation. In this talk we will present the phenomenological analysis of this theory by describing the world data on the $g_1$ and $g_1^h$ structure functions within the JAM global analysis framework . Beyond this, we investigate the qualitative behaviour of the quark and gluon hPDFs and the challenges involved with measuring them.
We consider the novel small-$x$ helicity evolution equations previously derived using the light-cone operator treatment (LCOT) [1,2]. In the double logarithmic approximation (summing powers of $\alpha_s\ln^2(1/x)$) and in the large-$N_c$ limit, the evolution yields a closed system of equations for which we construct an analytic solution. This solution can then provide small-$x$, large-$N_c$ expressions for the flavor-singlet quark and gluon helicity PDFs and TMDs along with the $g_1$ structure function, with their leading small-$x$ asymptotics given by
\begin{align}
\Delta \Sigma (x, Q^2) \sim \Delta G (x, Q^2)
\sim g_1 (x, Q^2) \sim \left( \frac{1}{x} \right)^{\alpha_h} , \notag
\end{align}
where the exact analytic expression we obtain for the intercept $\alpha_h$ can be approximated by $\alpha_h = 3.66074 \, \sqrt{\frac{\alpha_s \, N_c}{2 \pi}}$. Our solution also yields an all-order (in $\alpha_s$) resummed small-$x$ anomalous dimension $\Delta \gamma_{GG} (\omega)$ which agrees with the fixed-order calculations to the existing three-loop order. Notably, our anomalous dimension slightly disagrees at 4 loops with that obtained in the infrared evolution equation framework by Bartels, Ermolaev, and Ryskin (BER) [3] (the latter also agrees with the existing 3-loop calculations).
Despite the previously reported agreement at the two decimal points [2], the intercepts of our large-$N_c$ helicity evolution and that of BER disagree beyond that precision, with the BER intercept at large $N_c$ being equal to $\alpha_h^{BER} = 3.66394 \, \sqrt{\frac{\alpha_s \, N_c}{2 \pi}}$. We speculate on the origin of this disagreement.
[1] Y. V. Kovchegov, D. Pitonyak and M. D. Sievert, Helicity Evolution at Small-x, JHEP 01 (2016) 072, [1511.06737].
[2] F. Cougoulic, Y. V. Kovchegov, A. Tarasov and Y. Tawabutr, Quark and gluon helicity evolution at small x: revised and updated, JHEP 07 (2022) 095, [2204.11898]
[3] J. Bartels, B. I. Ermolaev and M. G. Ryskin, Flavor singlet contribution to the structure function G(1) at small x, Z. Phys. C 72 (1996) 627–635, [hep-ph/9603204].
Double spin asymmetries for particle and jet productions in longitudinally polarized proton-proton collisions are among the key measurements at RHIC to extract the spin fraction of gluons inside the proton. Although next-to-leading order perturbative QCD predictions have been quite successful in fitting experimental data within the RHIC kinematics, to constrain gluons at even smaller x, one needs theoretical predictions including the small x evolution and gluon saturation effect. In this talk, I will present our efforts towards completing this task. To be specific, we have calculated the longitudinal double spin asymmetry for soft gluon production at midrapidity in the small x regime. Our result is expressed in terms of polarized Wilson lines and is related to quark and gluon helicity distribution of the proton at small x. The result can also provide valuable information on phenomenology related to small x helicity evolution.
We study the small-$x$ asymptotics of the flavor non-singlet T-odd leading-twist quark transverse momentum dependent parton distributions (TMDs). While the leading eikonal small-$x$ asymptotics of the quark Sivers function is given by the spin-dependent odderon, we are interested in revisiting the sub-eikonal correction considered by us earlier. We first simplify the expression for the TMD at small Bjorken $x$ and then construct small-$x$ evolution equations for the resulting operators in the large-$N_c$ limit, with $N_c$ the number of quark colors. The evolution equations resum all powers of the double-logarithmic parameter $\alpha_s \, \ln^2 (1/x)$, where $\alpha_s$ is the strong coupling constant, which is assumed to be small. Solving these evolution equations numerically, we arrive at the following leading small-$x$ asymptotics at large $N_c$:
\begin{align}
f_{1 \: T}^{\perp \: NS} (x \ll 1 ,k_T^2) & = C_O (x, k_T^2) \, \frac{1}{x} + C_1 (x, k_T^2) \, \left( \frac{1}{x} \right)^{3.4 \, \sqrt{\frac{\alpha_s \, N_c}{4 \pi}}} , \notag
\end{align}
The functions $C_O (x, k_T^2)$ and $C_1 (x, k_T^2)$ can be readily obtained in our formalism: they are mildly $x$-dependent and do not strongly affect the
power-of-$x$ asymptotics shown above. The function $C_O$, along with the $1/x$ factor, arises from the odderon exchange. For the sub-eikonal contribution to the quark Sivers function (the term with $C_1$), our result shown above supersedes the one obtained in our previous work due to the new contributions identified recently.
Electroweak Physics and Beyond the Standard Model
Latest results on Z boson measurements are presented using collision data collected by CMS up to now. Differential production cross section measurements on several observables will be discussed.
Precision measurements of the production cross-sections of W/Z boson at LHC provide important tests of perturbative QCD and information about the parton distribution functions for quarks within the proton. Extremely precise double-differential measurement of Z transverse momentum and rapidity at centre-of-mass energy of 8 TeV will be presented. Also, the transverse momentum of the W and Z boson measured from the hadronic recoil at 5 and 13 TeV will be discussed. We will also present a measurement of Z decays to a pair of leptons and a photon, which is a sensitive test of the kinematics of final-state QED radiation. Finally, if available, the measurement of the W, Z, ttbar cross section and their ratios at the centre-of-mass energy of 13.6 TeV using early Run3 data will be shown. These measurements are corrected for detector inefficiency and resolution and compared with state-of-the-art theoretical calculations.
Recent results on the EW sector from the CMS Collaboration will be presented.
The weak mixing angle is a probe of the vector-axial coupling structure of electroweak interactions. It has been measured precisely at the $Z$-pole by experiments at the LEP and SLD colliders, but its energy dependence above $𝑚_Z$ remains unconstrained.
In this contribution we propose to exploit measurements of Neutral-Current Drell-Yan at large invariant dilepton masses at the Large Hadron Collider to determine the scale dependence of the weak mixing angle in the $\overline{MS}$ renormalisation scheme, $\sin^2\theta_W(\mu)$.
Such a measurement can be used to test the Standard Model predictions for the $\overline{MS}$ running at TeV scales, and to set model-independent constraints on new states with electroweak quantum numbers.
To this end, we present an implementation of $\sin^2\theta_W(\mu)$ in the Powheg-Box Monte Carlo event generator, which we use to explore the potential of future analyses with the LHC Run3 and High-Luminosity datasets. In particular, the impact of higher order electroweak corrections and of the uncertainties due the knowledge of parton distribution functions are studied.
Precision theory predictions are crucial for interpreting LHC data. In
this talk, we present our public code and predictions for Drell-Yan
production up to the order N3LO, including transverse momentum
resummation up to N4LLp. We discuss the impact of these higher-order
corrections and compare them with experimental data. Furthermore, we
investigate the influence of N3LO parton distribution functions on the
precision of our predictions. Finally, we discuss recent advancements in
jet-veto resummation at N3LLp+NNLO for boson and diboson processes. The
public availability of our code allows experimental analyses to easily
and directly compare their results with higher-order predictions.
In the Standard Model, the ground state of the Higgs field is not found at zero but instead corresponds to one of the degenerate solutions minimising the Higgs potential. In turn, this spontaneous electroweak symmetry breaking provides a mechanism for the mass generation of nearly all fundamental particles. The Standard Model makes a definite prediction for the Higgs boson self-coupling and thereby the shape of the Higgs potential. Experimentally, both can be probed through the production of Higgs boson pairs (HH), a rare process that presently receives a lot of attention at the LHC. In this talk, the latest HH searches by the ATLAS experiment are reported, with emphasis on the results obtained with the full LHC Run 2 dataset at 13 TeV. Non-resonant HH search results are interpreted both in terms of sensitivity to the Standard Model and as limits on the Higgs boson self-coupling and the quartic VVHH coupling. The Higgs boson self-coupling can be also constrained by exploiting higher-order electroweak corrections to single Higgs boson production. A combined measurement of both results yields the overall highest precision, and reduces model dependence by allowing for the simultaneous determination of the single Higgs boson couplings. Results for this combined measurement are also presented. Finally, extrapolations of recent HH results towards the High Luminosity LHC upgrade are also discussed.
Determining the CP property of the Higgs boson is important for a precision test of the Standard Model as well as for the search for new physics. We propose a novel jet substructure observable based on the azimuthal anisotropy in a linearly polarized gluon jet that is produced in association with a Higgs boson at hadron colliders, and demonstrate that it provides a new CP-odd observable for determining the CP property of the Higgs-top interaction. We introduce a factorization formalism to define a polarized gluon jet function with the insertion of an infrared-safe azimuthal observable to capture the linear polarization.
The large integrated luminosity collected by the ATLAS detector at the highest proton-proton collision energy provided by LHC allows to probe the presence of new physics that could enhance the rate of very rare processes in the SM. The LHC can therefore gain considerable sensitivity for Flavour Changing Neutral Current (FCNC) interactions of the top quark. In the SM, FCNC involving the top-quark decay to another up-type quark and a neutral boson are so small that any measurable branching ratio for such a decay is an indication of new physics. The ATLAS experiment has performed searches for FCNC couplings of the top quark with a photon, gluon, Z boson or Higgs boson. In this contribution, the most recent results are presented, which include the complete data set of 139/fb at 13 TeV collected at the LHC during run 2 (2015-2018). The large data set, together with improvements in the analysis, yields a strong improvement of the expected sensitivity compared to previous experiments and partial analyses of the LHC data. Another example of a rare SM process sensitive to new physics processes is the 4-top production. The latest results for this process will be presented and the experimental challenges and systematic uncertainties will be discussed.
The Drell-Yan lepton pair productions have been measured to an unprecedented precision level at the LHC. In companion, the theoretical calculations should reach the same level. However, a visible discrepancy among different next-to-next-to-leading order (NNLO) calculations has been discovered by both the CTEQ-TEA group and also by S. Alekhin~\emph{et al.} In this study, we carefully examine the difference among different NNLO codes, and also compare with the $q_T$ resummatiom calculation. We explore the impacts of different calculations on the proton PDFs through the CTEQ-TEA global analysis, based on the latest Drell-Yan data from ATLAS, CMS, and LHCb groups.
For the CTEQ-TEA Collaboration
We present predictions of the cross section of high-energy neutrino-nucleon scattering.
The calculations are based on CT18NNLO parton distribution functions, and their uncertainties. For the highest energies, we extrapolate the PDFs to small x according to several assumptions, which affect the uncertainties at such high energies.
The results can be applied to astrophysical neutrino observatories, such as IceCube currently and proposed future detectors.
Accurate theory calculations for neutrino-nucleus scattering rates are essential in the interpretation of neutrino experiments, from oscillation measurements to astroparticle physics at neutrino telescopes. In the deep-inelastic (DIS) regime, neutrino structure functions can be reliably evaluated in the framework of perturbative QCD (pQCD). However, large uncertainties affect these structure functions at low momentum transfer, $Q \leq 2~\mathrm{GeV}$, distorting event rate predictions for energies up to $E_\nu \sim 1~\mathrm{TeV}$. We present a determination of the neutrino inelastic structure functions valid for all values of $Q^2$, from the resonance region to ultra-high energies. Our approach combines a data-driven machine learning parametrisation of neutrino structure functions at low and moderate $Q^2$ values matched to perturbative QCD calculations at large $Q^2$. We compare our results to other calculations in the literature, in particular with BGR18 and the Bodek-Yang model, and outline the implications for neutrino scattering experiments at the LHC such as Faser$\nu$ and the Forward Physics Facility.
Recasting phenomenological Lagrangians in terms of SM effective field theory (SMEFT) provides a valuable means of connecting potential BSM physics at momenta well above the electroweak scale to experimental signatures at lower energies. We jointly fit the Wilson coefficients of SMEFT operators as well as the PDFs in an extension of the CT18 global analysis framework, obtaining self-consistent constraints to possible BSM physics effects. Global fits are boosted with machine-learning techniques in the form of neural networks to ensure efficient scans of the full PDF+SMEFT parameter space.
QCD with Heavy Flavours and Hadronic Final States
We discuss the reconstruction of target jet and the framework of quantifying its internal substructure. Due to momentum and charge conservation, target and current correlation can be exploited which significantly constrains the event-wide particle distributions. We demonstrate this method using Pythia simulations of electron-proton collisions in the context of identifying the flavor of the struck quark jet. We also quantify the detector requirement for systematically covering the target jet region in order to exploit such information, which will be useful for forward detector designs. Extensions to electron-ion collisions and studies using BeAGLE simulations will be discussed.
The substructure of QCD jets has been the subject of intense investigation following the development of infrared and collinear safe clustering algorithms and observables. A particularly illuminating observable to study the radiation patterns of light and heavy partons is the Lund jet plane (LJP), where various types of emissions such as soft-collinear, hard-collinear, and non-perturbative emissions as well as initial-state radiation and underlying event can be separately identified. By reclustering jets using the Cambridge/Aachen algorithm, then declustering them following the hardest/heavy-flavor branch, we can construct a representation of the LJP. This poster presents a status update on the LJP for light-, charm-, and beauty-initiated jets at the LHCb experiment, a well-optimized forward detector for studying heavy flavor physics. We expect mass effects to be revealed in various regions of the LJP such as the leading particle effect and the dead-cone effect.
Jets are collimated sprays of final-state particles produced from initial high-momentum-transfer partonic (quark/gluon) scatterings in particle collisions. Since jets are multi-scale objects that connect asymptotically free partons to confined hadrons, jet substructure measurements in vacuum can provide insight into the parton evolution and the ensuing non-perturbative hadronization processes. Experimentally, jet measurements need to be corrected for detector effects to be compared with theoretical calculations and model predictions. The traditional correction procedure uses Bayesian inference in as many as three dimensions and requires the observables to be binned. A novel correction procedure, MultiFold, uses the machine learning technique to correct with higher dimensionality in an un-binned fashion. Furthermore, MultiFold is potentially more desirable because it accounts for the correlation in the multi-dimensional observable phase space. In this measurement, we have applied this technique for the first time to hadronic collision data.
The STAR experiment recorded data for $\sqrt{s} = 200$ GeV $pp$ collisions in 2012. Using this dataset, we reconstruct jets with charged particle tracks measured in the Time Projection Chamber and neutral particles measured in the Barrel Electromagnetic Calorimeter. After fully correcting six jet observables ($p_\mathrm{T}$, $Q^{\kappa}$, $M$, $M_g$, $R_g$ and $z_g$) simultaneously for detector effects using MultiFold, we present a selection of corrected observables and the correlations among them and compare them to Monte Carlo event generators. Such correlation measurements between jet observables allow for the study of parton shower and hadronization on a jet-by-jet basis. For example, by measuring the correlation between a SoftDrop observable and a collinear drop observable, we learn about the interplay between non-perturbative and perturbative processes.
Various measurements related to the study of hadronic jets substructure in proton collisions at 13 TeV with the CMS experiment are presented. The differential jet production cross section as a function of the jet mass and transverse momentum is shown in events with a Z boson plus jet topology, with and without the soft radiation within a jet removed by a jet grooming algorithm. Measurement of jet substructure observables describing the distribution of particles within quark- and gluon-initiated jets, are carried out with both dijet and Z plus jet event samples. The cross section of hadronically decaying W/Z bosons identified using jets with a large cone radius at large transverse momenta together with jet substructure identification criteria, are also presented.
The production mechanism of quarkonia in $p$+$p$ collisions involves both the perturbative and non-perturbative QCD processes and is a topic of active investigation. Quarkonium production from Color Singlet Model and Color Octet Mechanism is expected to result in different jet activities, i.e., the number of jets associated with quarkonium creation, due to different numbers of emitted hard partons. Therefore, the study of $J/\psi$ production with respect to jet activity could potentially be used to differentiate between the different production mechanisms.
In this talk, we will present the first measurement of the $J/\psi$ production cross section as a function of jet activity in $p$+$p$ collisions at $\sqrt{s}$ = 200 GeV from the STAR experiment. These results are compared to the PYTHIA calculations, and physics implications will be discussed.
We present the recent and ongoing developments with respect to the use of machine learning methods in models of hadronization as implemented in general purpose event generators. Specifically we focus on the performance of generative machine learning algorithms in reproducing Pythia-simulated hadronization kinematics and global observables. Finally, we will discuss the inclusion of error estimates within the machine-learning-based hadronization pipeline and progress in implementing a machine-learning-improved model of hadronization.
The LHC produces a vast sample of top quark pairs and single top quarks. Measurements of the inclusive top quark production rates at the LHC have reached a precision of several percent and test advanced Next-to-Next-to-Leading Order predictions in QCD. Differential measurements in several observables are important to test SM predictions and improve Monte Carlo generator predictions. In this contribution, comprehensive measurements of top-quark-antiquark pair and single-top-quark production are presented that use data recorded by the ATLAS experiment in the years 2015-2018 during Run 2 of the LHC. A recent result from the 5 TeV operation of the LHC is also included, which already challenges the precision of the 13 TeV cross-section measurement. In addition, a first look into top-quark pair production in run 3 data at 13.6 TeV is given.
The remarkably large dataset collected with the ATLAS detector at the highest proton-proton collision energy provided by LHC allows to use the large sample of top quark events to test theoretical predictions with unprecedented precision. Recent highlights are the new measurement of W-boson polarisation in ttbar events single-top quark polarisation, new top-quark mass measurements as well as distributions sensitive to colour reconnection and b-qhark fragmentation.
We present the first measurement of two-particle angular correlations of charged particles emitted in high energy $e^+e^-$ annihilation up to $\sqrt{s}=$209~GeV and anti-kT jet energy spectrum and substructure measurements using the archived ALEPH $e^+e^-$ data taken between 1992 and 2000.
The correlation functions are measured as a function of charged particle multiplicity for the first time with LEP2 data. The correlation is measured with both the lab- and the thrust coordinate systems, with the latter sensitive to potential medium expanding transverse to the color string in an $e^+e^-\rightarrow q\bar{q}$ topology. Results with $e^+e^-$ data at higher collision energy up to 209 GeV will also be presented with a high event multiplicity reach. A hint of a tantalizing structure emerges in high multiplicity $e^+e^-$ events that is not seen in their low multiplicity and low energy counterparts.
The jets are reconstructed with the anti-k$_T$ algorithm with a resolution parameter of 0.4. It is the cleanest test of jets and QCD without the complication of hadronic initial states. The fixed center-of-mass energy allows the first direct test of pQCD calculation. The measurements are compared to predictions from MC generators and two perturbative QCD calculations at NLO and with NLL’+R resummation.
These results also serve as important baseline to compare to similar measurements in other colliding systems, as well as expanding our search for collective phenomena in a new phase space in the $e^+e^-$ collision system for a potential discovery. Future directions, including testing jet clustering algorithms designed for future electron-ion collider experiments, as well as connections to heavy ion collisions, will also be discussed.
Spin and 3D Structure
The so-called Generalized Parton Distribution (GPDs) contain information about the parton's transverse position versus their longitudinal momentum, and can be accessed in hard exclusive reactions (where all products are known). Most of the current models rely on Deeply Virtual Compton Scattering (DVCS) measurements in their parametrization. However, extracting GPDs from other channels will provide us with unique and new information that can't be accessed with solely one channel. For instance, GPDs extracted from Timelike Compton Scattering (TCS), the "timelike equivalent" of DVCS, is enabling study of GPD's universality and of NLO effects. Double Deeply Virtual Compton Scattering (DDVCS) allows to extract GPDs in a broad range of kinematic points, not accessible with DVCS and TCS, which are essential for some of the GPD's interpretations, such as obtaining tomographic pictures of the nucleon. In this presentation, we would like to present our experimental program for Jefferson Lab Hall C aiming at the measurement of TCS and DDVCS in a complementary approach to DVCS, and possible extension to hard exclusive vector mesons measurements. We will discuss interpretations and physics outcome, as well as our efforts in developing a new muon detector for DDVCS measurements.
Generalized Parton Distributions (GPDs) have been one of the most important tools to access the nucleon 3D structure including its mass, angular momentum and mechanical properties. However, the extraction of GPDs has been challenging due to its high-dimension nature. Recent progress in lattice QCD have brought in many insights into the studies of GPDs. In this talk I will introduce the GPDs through Universal Moment Parameterization (GUMP) program which aims to combine these lattice inputs together with various experimental measurements to obtain the state-of-the-art GPDs from global analysis.
Deeply virtual exclusive reactions encode the dynamics of bound partons in hadrons through 3D quantum mechanical correlation functions - the generalized parton distributions; however, there are many levels of abstraction in the analysis from experimental data to information on hadron structure. There is an immediate need to develop advanced phenomenology and computational tools in preparation for the comprehensive exclusive reaction program planned for the upcoming EIC. The FemtoNet framework was developed to answer this call by reframing the analysis of exclusive experiments as a quantification of information loss and reconstruction through the many inverse problems encountered. FemtoNet utilizes physics-informed deep learning models whose architectures are specifically designed to inherently satisfy physics constraints in their predictions. The FemtoNet framework also leverages a suite of uncertainty quantification techniques to separate reducible and irreducible errors from the analysis and properly propagate experimental uncertainty. I will demonstrate what physics-informed deep neural networks are capable of in the context of reconstructing lost information from inverse problems in exclusive scattering experiments and give prospects for the future of such a program and consequences for an EIC.
I will present a framework for the analysis of deeply virtual exclusive scattering experiments to enable the extraction of observables from data with a faithful representation of uncertainty. The extraction is focused on obtaining the different quark flavor and scale dependence of the various observables at NLO in perturbative QCD, while using the azimuthal phase dependence as a discriminant of twist three terms. Establishing benchmarks in both the phenomenology and computational/machine learning sectors is critical to this effort which is poised for optimizing and generalizing the information extracted from data.
Mapping the 3D structure of the proton in terms of its spinning quark and gluon constituents is one of the main goals of current hadronic physics investigations, especially the field of femtography. Generalized parton distributions (GPDs) contribute to solving this problem. Fourier transforms of GPDs give single particle spatial densities of quarks and gluons for particular longitudinal momentum fractions, x. The physical properties derived from GPDs include the average radius of each partonic component of the nucleon and other quantities. In addition to these one-particle densities, a fuller dynamical picture of the proton’s interior can be obtained by introducing two-particle spatial density distributions. To capture the proton’s internal structure, information on the relative position between partons is crucial; two-particle densities give such relative positions between the quarks and gluons in the transverse plane. Two-particle densities depend on two spatial variables, which can be chosen to be the relative particle motion and the center-of-momentum motion; they can, therefore, provide a measure of the correlations in the particles’ motion. Connecting the two-body densities to observables, we show that two-particle densities can be defined in QCD with generalized double parton distributions (GDPDs). Using GDPDs, we can describe nucleons’ quark and gluon dynamics through overlap probabilities. Such quantities allow us to extract information from data on the geometric structure of the proton; we can determine whether the gluons cluster around valence quarks, or if they are distributed in a diffused cloud within the proton.
Generalized parton distributions (GPDs) are important non-perturbative functions that provide tomographic images of partonic structures of hadrons. We introduce a type of exclusive processes for a better study of GPDs, which we refer to as single diffractive hard exclusive processes (SDHEPs), and give a general proof for their factorization into GPDs. We demonstrate that the SDHEP is not only sufficiently generic to cover all the known processes for extracting GPDs, but also well motivated for the search of new processes for the study of GPDs. We also examine the sensitivity of the SDHEP to the parton momentum fraction $x$ dependence of GPDs, by examining two processes that can be readily measured at J-PARC and JLab, respectively.
Transverse Single Spin Asymmetries (TSSAs) in transversely polarized proton-proton collisions ($p^{\uparrow}+p$) have been a fruitful source for studying the spin structure of the proton. In the 2015 RHIC data taking periods, collisions of polarized protons with nuclei ($p^{\uparrow}+A$) were studied for the first time. The measurements of TSSAs in $p^{\uparrow}+p$ and $p^{\uparrow}+A$ collisions can provide a unique opportunity to investigate the origin of TSSA in gluon-rich target nuclei and provide a tool to study nuclear effects in $p+A$ collisions. This presentation will report PHENIX results of TSSAs for charged hadrons ($h^{\pm}$) at forward and backward rapidity ($1.4<|\eta|<2.4$) over the transverse momentum range $1.25
There have been numerous attempts in the last couple of decades to understand the origin of the unexpectedly large transverse single spin asymmetry ($A_{N}$) of inclusive hadron production at forward rapidities observed in $p^{\uparrow}$+$p$ collisions at different center-of-mass energies ($\sqrt{s}$). The current theoretical framework to explain such a puzzle includes the twist-3 contributions in the collinear factorization framework, and the transverse-momentum-dependent contributions from the initial-state quark and gluon Sivers functions and/or final-state Collins fragmentation functions. However, there are indications that the large $A_{N}$ might come from diffractive processes, according to the previous analyses of $A_{N}$ for forward $\pi^{0}$ and electromagnetic jets in $p^{\uparrow}$+$p$ collisions at STAR [1]. The STAR Forward Meson Spectrometer (FMS) is an electromagnetic calorimeter, which can detect photons, neutral pions, and eta mesons, with a pseudorapidity coverage of $2.6 < \eta < 4.2$. In 2015 and 2017, STAR collected large $p^{\uparrow}$+$p$ data sets at $\sqrt{s}= 200 $ GeV and $\sqrt{s}= 510 $ GeV, which provide a great opportunity to measure $A_{N}$ for inclusive and diffractive electromagnetic jets. In this talk, we will present the preliminary results and analysis updates on $A_{N}$ for inclusive and diffractive electromagnetic jets in the FMS at $\sqrt{s} = 200$ GeV and $510$ GeV. Also, we will present the comparison of $A_{N}$ between inclusive and diffractive electromagnetic jets.
[1] (STAR) J. Adam et al., Phys. Rev. D 103, 092009 (2021)
In the high-energy $p+p$ collisions, the transverse single spin asymmetry for very forward neutron production has been interpreted by an interference between $\pi$ (spin flip) and $a_1$ (spin non-flip) exchange with a non-zero phase shift. The $\pi$ and $a_1$ exchange model predicted the neutron asymmetry would increase in magnitude with transverse momentum ($p_{\scriptsize{\textrm{T}}}$) in $p_{\scriptsize{\textrm{T}}} < 0.4$ GeV/$c$. In June 2017, the RHICf experiment installed an electromagnetic calorimeter at the zero-degree area of the STAR experiment at the Relativistic Heavy Ion Collider and measured the neutron asymmetry in a wide $p_{\scriptsize{\textrm{T}}}$ range of $0 < p_{\scriptsize{\textrm{T}}} < 1$ GeV/$c$ from polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV. The RHICf data allows us to study the kinematic dependence of the neutron asymmetry in detail, which not only can test the $\pi$ and $a_1$ exchange model in the wider $p_{\scriptsize{\textrm{T}}}$ range but also can enrich our understanding for the spin-involved diffractive particle production mechanism. We present the final result of the neutron asymmetry measured by the RHICf experiment. A new theoretical trial to understand the RHICf result based on the Reggeon exchange will also be discussed.
Using the light-front wave functions (LFWFs) overlap representation, we built a theoretical model for the pion state, that parametrizes different pion parton distribution functions. The model is constructed with two sets of parameters, that can be fitted separately by performing two independent fits: one for the collinear, and one for the transverse direction.
At present, we have been able to fit observables sensible to the pion collinear parton distribution function (PDF), and the existing experimental data of the pion electromagnetic form factor.
Moreover, there is some work in progress in the direction to compute the pion generalized parton distributions (GPDs) and to predict the values of certain observable seinsible to pion GPDs. In future, we plan to fit also the experimental data sensible to the pion transverse momentum dependent parton distribution functons (TMDs).
It is known that the trace anomaly in the QCD energy-momentum tensor $T^{\mu \nu}$ can be attributed to the anomalies for each of the gauge-invariant quark part and gluon part of $T^{\mu \nu}$, and their explicit three-loop formulas have been derived in the $\overline{\rm MS}$ scheme in the dimensional regularization. The matrix elements of this quark/gluon decomposition of the QCD trace anomaly allow us to derive the QCD constraints on the hadron's gravitational form factors, in particular, on the twist-four gravitational form factors, $\bar{C}_{q,g}$. Using the three-loop quark/gluon trace anomaly formulas, we calculate the forward (zero momentum transfer) value of the twist-four gravitational form factors $\bar{C}_{q,g}$ at the NNLO accuracy. We present quantitative results for nucleon as well as for pion, leading to a model-independent determination of the forward value of $\bar{C}_{q,g}$. We find quite different pattern in the obtained results between the nucleon and the pion. In particular, for the nucleon, the present information from experiment and lattice QCD on the nonperturbative matrix elements arising in our NNLO formula allows us to obtain a prediction of the forward value of $\bar{C}_{q,g}$ at the accuracy of a few percent level. This talk is based on arXiv:2209.14367 and a new preprint which will appear in arXiv in a few days.
As one of the essential building blocks of ordinary matter, understanding the proton and the strong force that binds its constituents are of crucial importance. At low $Q^2$, the perturbative description of QCD fails, and it is necessary to employ effective theories such as Chiral Perturbation Theory. One way of directly testing these effective theories is the measurement of polarizabilities, which describe the ensemble response of the nucleon to an external field. In this talk, I will present the recently published measurements of several proton spin polarizabilities from the Jefferson Lab E08-027 (g2p) collaboration, $\delta_{LT}$ and $\overline{d_2}$, as well as the first low $Q^2$ measurement of the proton's $g_2$ structure function, which is used to extract these moments. These results are used to directly check several competing calculations from Chiral Perturbation Theory and act as a direct test on our understanding of QCD in the regime where the proton's constituents interact strongly.
Future Experiments
The EIC physics program relies on successful measurements of exclusive final states, which produce charged particles (e.g. protons, pions) at far-forward pseudorapidities. Such particles are within a few millimeters of the outgoing hadron beam. Reconstruction of these particles requires use of silicon detectors placed directly into the accelerator vacuum, in the style of the Roman Pots used at HERA, RHIC, and the LHC, but without the “pots” which are customarily used. However, unlike past and present facilities, the broad range of energies and collision species at the EIC provides a unique challenge in accurately reconstructing the momenta of these far-forward particles, especially in cases where the particles come from nuclear breakup, such as is the case in spectator-tagged DIS measurements. Additionally, some final states such as those of interest for meson structure studies, the particles of interest decay in flight, complicating accurate reconstruction further. In this talk, we discuss the current state of these efforts in the development of the EIC exclusive physics program, and show updates on recently funded generic R&D which aims to further refine and standardize the reconstruction of such final states.
A new era of hadron collisions will start around 2029 with the High-Luminosity LHC which will allow to collect ten times more data than what has been collected during 10 years of operation at LHC. This will be achieved by higher instantaneous luminosity at the price of higher number of collisions per bunch crossing.
In order to withstand the high expected radiation doses and the harsher data taking conditions, the ATLAS Liquid Argon Calorimeter readout electronics will be upgraded.
The electronic readout chain is composed of four main components.
1: New front-end boards will allow to amplify, shape and digitise the calorimeter’s ionisation signal on two gains over a dynamic range of 16 bits and 11 bit precision. Low noise below Minimum Ionising Particle (MIP), i.e. below 120 nA for 45 ns peaking time, and maximum non-linearity of two per mille are required. Custom preamplifiers and shapers are being developed to meet these requirements using 65 nm and 130 nm CMOS technologies. They shall be stable under irradiation until 1.4kGy (TID) and 4.1x10^13 new/cm^2 (NIEL). Two concurrent preamp-shaper ASICs were developed and, “ALFE”, the best one has been chosen. The test results of the latest version of this ASIC will be presented. “COLUTA”, a new ADC chip is also being designed. A production test setup is being prepared and integration tests of the different components (including lpGBT links developed by CERN) on a 32-channels front-end board are ongoing, and results of this integration will be shown.
2: New calibration boards will allow the precise calibration of all 182468 channels of the calorimeter over a 16 bits dynamic range. A non-linearity of one per mille and non-uniformity between channels of 0.25% with a pulse rise time smaller than 1ns shall be achieved. In addition, the custom calibration ASICs shall be stable under irradiation with same levels as preamp-shaper and ADC chips. The HV SOI CMOS XFAB 180nm technology is used for the pulser ASIC, “CLAROC”, while the TSMC 130 nm technology is used for the DAC part, “LADOC”. The latest versions of those 2 ASICs which recently passed the production readiness review (PDR) with their respective performances will be presented.
3: New ATCA compliant signal processing boards (“LASP”) will receive the detector data at 40 MHz where FPGAs connected through lpGBT high-speed links will perform energy and time reconstruction. In total, the off-detector electronics receive 345 Tbps of data via 33000 links at 10 Gbps. For the first time, online machine learning techniques are considered to be used in these FPGAs. A subset of the original data is sent with low latency to the hardware trigger system, while the full data are buffered until the reception of trigger accept signals. The latest development status of the board as well as the firmware will be shown.
4: A new timing and control system, “LATS”, will synchronise to the aforementioned components. Its current design status will also be shown.
The ATLAS Muon Spectrometer is designed to provide Muon triggering, identification and momentum measurement. It consists of resistive plat chambers (RPCs) and thin gap chambers (TGCs) that are used as primary trigger detectors, while monitored drift tubes (MDTs) and cathode strip chambers (CSCs) are utilized for precision trackering. To improve the Muon transverse momentum (pT) resolution at L0 triggering for the future high-luminosity LHC (HL-LHC) run, MDT chamber data will be included at the first trigger level. The current MDT chambers (inner barrel) will be replaced by RPC and sMDT chambers to allow for 3-station RPC triggering. With the improved MDT triggering, roughly 75% low momentum muons (pT < 20GeV) can be rejected and the efficiency curve become much sharper. Additionally, coping with the much higher hit rates in HL-LHC, MDT readout electronics system face great challenges and much be upgraded. The main challenges are providing much higher data bandwidth, maintaining low power consumption, surviving in harsher radiation environment and complying with mechanical rule from legacy system.
This submission concerns the upgrade of front-end (FE) electronics for the MDT detector sub-system. The front-end (FE) system is made up of mezzanine cards and Chamber Service Modules (CSM) modules. For the new mezzanine card, it will operate in a trigger-less mode to handle the high collision rate compared to the detector trigger time. The ASD and TDC chips on the mezzanine are upgraded accordingly to provide higher readout bandwidth for the trigger-less operation. In total, roughly 80k ASDs and 22k TDCs will be produced for HL-LHC MDT detector. The new CSM module must handle both legacy and new mezzanines as there are some mezzanines cannot be accessed for replacement. The new CSM is based on the CERN LpGBT chipsets to take advantage of radiation-hard features. The latency of the CSM is fixed and the output bandwidth is up to 20Gbps. In total, roughly 1200 CSM modules will be delivered for installation eventually.
The Large Hadron Collider (LHC) at CERN is the largest and most powerful particle collider today. The Phase-II Upgrade of the LHC will increase the instantaneous luminosity by a factor of 7 leading to the High Luminosity LHC (HL-LHC). At the HL-LHC, the number of proton-proton collisions in one bunch crossing (called pileup) increases significantly, putting more stringent requirements on the LHC detector electronics and real-time data processing capabilities.
The ATLAS Liquid Argon (LAr) calorimeter measures the energy of particles produced in LHC collisions. This calorimeter also feeds the ATLAS trigger to identify interesting events. In order to enhance the ATLAS detector physics discovery potential, in the blurred environment created by the pileup, an excellent resolution of the deposited energy and an accurate detection of the deposited time are crucial.
The computation of the deposited energy will be performed in real-time using dedicated data acquisition electronic boards based on FPGAs. FPGAs are chosen for their capacity to treat large amounts of data with very low latency. The computation of the deposited energy is currently done using optimal filtering algorithms that assume a nominal pulse shape of the electronic signal. These filter algorithms are adapted to the LHC conditions with very limited pileup and no timing overlap of the electronic pulses in the detector. However, with the increased luminosity and pileup at HL-LHC, the performance of the filter algorithms decreases significantly and no further extension nor tuning of these algorithms could recover the lost performance.
The off-detector electronic boards for the Phase-II Upgrade of the LAr calorimeter will use the next high-end generation of INTEL FPGAs with increased processing power and memory. This is a unique opportunity to develop the necessary tools, enabling the use of more complex algorithms on these boards. We developed several neural networks (NNs) with significant performance improvements with respect to the optimal filtering algorithms. The main challenge is to efficiently implement these NNs into the dedicated data acquisition electronics. Special effort was dedicated to minimising the needed computational power while optimising the NNs architectures.
Five NN algorithms based on CNN, RNN, and LSTM architectures will be presented. The improvement of the energy resolution and the accuracy on the deposited time compared to the legacy filter algorithms, especially for overlapping pulses, will be discussed. The implementation of these networks in firmware will be shown. Two implementation categories in VHDL and Quartus HLS code are considered. The implementation results on Stratix 10 INTEL FPGAs, including the resource usage, the latency, and operation frequency will be reported. Approximations for the firmware implementations, including the use of fixed-point precision arithmetic and lookup tables for activation functions, will be discussed. Implementations including time multiplexing to reduce resource usage will be presented. We will show that two of these NNs implementations are viable solutions that fit the stringent data processing requirements on the latency (O(100ns)) and bandwidth (O(1Tb/s) per FPGA) needed for the ATLAS detector operation. The results of the tests of one of the NNs on the hardware will be presented along with the test setup.
This development is completely new and targets a technological breakthrough in the usage of neural networks implemented in readout electronic boards of particle physics detectors. We show that this goal is achievable for the HL-LHC upgrade. The results from this work are published in a special edition of the Computing and Software for Big Science journal.
SND@LHC is a compact and stand-alone experiment to perform measurements with neutrinos produced at the LHC in a hitherto unexplored pseudo-rapidity region of 7.2 < 𝜂 < 8.6, complementary to all the other experiments at the LHC. The experiment is located 480 m downstream of IP1 in the unused TI18 tunnel. The detector is composed of a hybrid system based on an 800 kg target mass of tungsten plates, interleaved with emulsion and electronic trackers, followed downstream by a calorimeter and a muon system. The configuration allows efficiently distinguishing between all three neutrino flavours, opening a unique opportunity to probe physics of heavy flavour production at the LHC in the region that is not accessible to ATLAS, CMS and LHCb. This region is of particular interest also for future circular colliders and for predictions of very high-energy atmospheric neutrinos. The detector concept is also well suited to searching for Feebly Interacting Particles via signatures of scattering in the detector target. The first phase aims at operating the detector throughout LHC Run 3 to collect a total of 290 fb−1. The experiment was recently installed in the TI18 tunnel at CERN and has seen its first data. A new era of collider neutrino physics is just starting.
The IceCube Neutrino Observatory is a Cherenkov detector located at the South Pole, instrumented in a cubic kilometer of ice. The DeepCore subdetector, at the lower center of the IceCube array, has a denser configuration and has allowed us to see GeV-scale neutrinos, which improves the sensitivity to atmospheric neutrino oscillations. Precious reconstruction is critical to neutrino oscillation parameter measurements. This study employs convolutional neural networks (CNNs) to reconstruct neutrino interactions in the DeepCore detector. This talk discusses the result of the atmospheric muon neutrino disappearance analysis using the CNN-reconstructed neutrino sample and compares it to the existing worldwide measurements.
PERLE is a facility to probe high-current multiturn energy recovery to be built at IJClab in Orsay. Besides being a key step towards the use of this technology, one of the priorities established in the last European Strategy for Particle Physics [1], in top energy colliders, it will also provide a strong physics programme on its own. We review the status of PERLE and the steps from the Conceptual Design Report [2] to a Technical Design Report in 2023.
[1] C. Adolphsen et al., CERN Yellow Rep.Monogr. 1 (2022) 1-270, e-Print: 2201.07895 [physics.acc-ph].
[2] D. Angal-Kalinin et al., J. Phys. G 45 (2018) 6, 065003, e-Print: 1705.08783 [physics.acc-ph].
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end of this range (few GeV – ~TeV), while the region ~MeV to ~GeV is largely unexplored. Most of the stable constituents of known matter have masses in this lower range, tantalizing hints for physics beyond the Standard Model have been found here, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. It is therefore a priority to explore. If there is an interaction between light DM and ordinary matter, as there must be in the case of a thermal origin, then there necessarily is a production mechanism in accelerator-based experiments. The most sensitive way, (if the interaction is not electron-phobic) to search for this production is to use a primary electron beam to produce DM in ﬁxed-target collisions. The Light Dark Matter eXperiment (LDMX) is a planned electron-beam fixed-target missing-momentum experiment that has unique sensitivity to light DM in the sub-GeV range. This contribution will give an overview of the theoretical motivation, the main experimental challenges and how they are addressed, as well as projected sensitivities in comparison to other experiments.
The LUXE experiment (Laser Und XFEL Experiment) is an experiment in planning at DESY Hamburg using the electron beam of the European XFEL. LUXE is intended to study collisions between a high-intensity optical laser pulse and 16.5 GeV electrons from the XFEL electron beam, as well as collisions between the laser pulse and high-energy secondary photons. This will elucidate quantum electrodynamics (QED) at the strong-field frontier, where the electromagnetic field of the laser is above the Schwinger limit. In this regime, QED is non-perturbative. This manifests itself in the creation of physical electron-positron pairs from the QED vacuum, similar to Hawking radiation from black holes. LUXE intends to measure the positron production rate in an unprecedented laser intensity regime. The experiment has received a stage 1 critical approval (CD1) from the DESY management and is finalising its technical design report (TDR). It is expected to start running in 2025/6. An overview of the LUXE experimental setup and its challenges and progress will be given, along with a discussion of the expected physics reach in the context of testing QED in the non-perturbative regime.
Missing abstract
Future Experiments
A fixed target experiment, HERCULES, similar to HERMES but with 500 times higher electron-nucleon luminosity, at EIC will allow a big advance in hadron physics. The internal target with the polarized hadron beam also has an important physics program. The high intensity photon beam will allow to study photo-production of the $c\bar c$ excited states and recently discovered XYZ states. We will present the analysis of experiment luminosity and ideas on an initial physics program.
Long-baseline neutrino oscillation experiments present some of the most compelling paths towards beyond-the-standard-model physics through measurement of PMNS matrix elements and observation of the degree of leptonic CP violation. State-of-the-art long-baseline oscillation experiments, like NOvA and T2K, are currently statistically limited, however uncertainty in neutrino-nucleus scattering represent important sources of systematic uncertainty and will fundamentally affect the precision of future experiments like DUNE and Hyper-K, if not addressed. Neutrino cross section uncertainties can be reduced through high statistics measurement of neutrino interactions on light nuclei, but creating a detector with an appropriate light target has proved elusive since the hydrogen bubble chambers designed of the last century. Modern chamber-based dark matter detectors like the Scintillating Bubble Chamber have demonstrated that advances in sensor technology, computing, and automation would allow a modern bubble chamber to fully utilize the megawatt scale intensity LBNF beam through the use of high resolution and high speed cameras, novel triggering, and machine-learning based event reconstruction. This talk will review the broad physics program for the construction of a bubble chamber for use with neutrinos supplied by Fermilab.
Coherent electro-production of $J/\psi$ on $^4$He offers a unique opportunity to explore the gluonic component of its matter distribution directly. The gluonic matter form factor of $^4$He can be experimentally accessed by performing a measurement of the reaction $^4 He(e, e' ^4He)J/\psi$ where the $J/\psi$ is reconstructed via missing mass. Such measurement requires the coincidence detection of both scattered electrons and recoiling nuclei, and novel tagging detectors will be needed to reconstruct the recoiling $^4$He momentum starting at low kinetic energies. The measured differential cross sections over a wide range of $t$ will answer critical questions regarding the gluonic structure of $^4$He: Will gluonic matter clump identically and form a similar diffractive structure in the matter form factor? Will the gluonic matter have diffractive minima as it charge form factor at the same values of Q2, if any at all? In this talk, we will discuss the possible future experiments with a fixed target as well as similar studies at EIC.
This talk will discuss future tagged deep inelastic scattering (TDIS) measurements in Hall A of Jefferson Lab, which will directly probe the elusive mesonic content of the nucleon via the Sullivan process. The idea that the nucleon’s mesonic content could be explored through electron nucleon deep inelastic scattering has a long history with the Sullivan process. However, even after five decades of this idea, there is a scarcity of data on meson PDFs. The TDIS experiment will measure low momentum recoiling (and spectator) hadrons in coincidence with deep inelastically scattered electrons from hydrogen (and deuterium) targets. The recently installed and commissioned Hall A Super Bigbite Spectrometer, a large acceptance detector package, will be used to detect the electrons. For the hadron detection, a novel multiple time projection chamber (mTPC) is being developed. Through use of the mTPC, a tagging technique will enhance deep inelastic scattering from partons in the meson cloud and provide access to the pion and kaon structure functions in the valence regime. Since existing world data on light meson structure is extremely sparse and the TDIS measurements will be crucial for shedding light on such topics as emergent hadron mass. This talk will present an overview of the experiment and its status.
The Liquid Argon Calorimeters are employed by ATLAS for all electromagnetic calorimetry in the pseudo-rapidity region |η| < 3.2, and for hadronic and forward calorimetry in the region from |η| = 1.5 to |η| = 4.9. They also provide inputs to the first level of the ATLAS trigger. After successful period of data taking during the LHC Run-2 between 2015 and 2018 the ATLAS detector entered into the a long period of shutdown. In 2022 the LHC has restarted a new data taking period the Run-3 period should see an increase of luminosity and pile-up up to 80 interaction per bunch crossing.
To cope with this harsher conditions, a new trigger readout path has been installed during the long shutdown. This new path should improve significantly the triggering performances on electromagnetic objects. This will be achieved by increasing the granularity of the objects available at trigger level by up to a factor of ten.
The installation of this new trigger readout chain required also the update of the legacy system. More than 1500 boards of the precision readout have been extracted from the ATLAS pit, refurbished and re-installed. The legacy analog trigger readout that will remain during the LHC Run-3 as a backup of the new digital trigger system has also been updated.
For the new system 124 new on-detector boards have been added. Those boards that are operating in a radiative environment are digitizing the calorimeter trigger signals at 40MHz. The digital signal is sent to the off-detector system and processed online to provide the measured energy value for each unit of readout. In total up to 31Tbps are analyzed by the processing system and more than 62Tbps are generated for downstream reconstruction. To minimize the triggering latency the processing system had to be installed underground. The limited available space imposed a very compact hardware structure. To achieve a compact system, large FPGAs with high throughput have been mounted on ATCA mezzanines cards. In total no more than 3 ATCA shelves are used to process the signal from approximately 34000 channels.
Given that modern technologies have been used compared to the previous system, all the monitoring and control infrastructure is being adapted and commissioned as well.
This contribution will present the challenges of the installation, the commissioning and the milestones still to be completed towards the full operation of both the legacy and the new readout paths for the LHC Run-3.
Experimental uncertainties related to hadronic object reconstruction can limit the precision of physics analyses at the LHC, and so improvements in performance have the potential to broadly increase the impact of results. Recent refinements to reconstruction and calibration procedures for ATLAS jets and MET result in reduced uncertainties, improved pileup stability and other performance gains. In this contribution, selected highlights of these developments will be presented.
Hadronic object reconstruction is one of the most promising settings for cutting-edge machine learning and artificial intelligence algorithms at the LHC. In this contribution, selected highlights of ML/AI applications by ATLAS to particle and boosted-object identification, MET reconstruction and other tasks will be presented.
Muon reconstruction performance plays a crucial role in the precision and sensitivity of the Large Hadron Collider (LHC) data analysis of the ATLAS experiment. Using di-muon Resonances we are able to calibrate to per-mil accuracy the detector response for muons. Innovative techniques developed throughout the Run-2 period and during the collider's shut-down significantly improve the measurement of muon reconstruction, identification and calibration performance with these preliminary data. New analysis techniques are exploited which involve multivariate analyses for rejecting background hadrons from prompt leptons from the hard interactions as well as innovative in-situ corrections on data that reduce biases in muon momenta induced from residual detector displacements. We measure the reconstruction efficiencies and momentum performance measured with these methods. The results achieved are fundamental for improving the reach of measurements and searches involving leptons, such as Higgs decays to dimuons and ZZ or the first low mass and high mass searches in the beyond-the-standard model sector. This talk will present the recently released results on the muon reconstruction performance using the Run-3 data collected in 2022 by the ATLAS detector.
Presentation of the performance of the trigger system of the CMS experiment in Run 2 and the first year of Run 3 of the LHC.
The CMS experiment at CERN underwent several detector upgrades before the Large Hadron Collider (LHC) Run 3 started in 2022, delivering integrated proton collision luminosity of 38 fb-1 to CMS. LHC will continue with the planned proton-proton and lead ion collision programmes until the Run-3 concludes in 2025.
During High Luminosity operations (2029-2038), LHC is expected to deliver 3000 fb-1 to CMS at high instantaneous luminosity and pileup. Significant detector upgrades are in development to prepare for operations in these challenging conditions.
This presentation will give an overview of the status of the CMS experiment after the first year of Run 3, and a general overview and plans of scheduled upgrades for the High Luminosity LHC (Phase-2).
We review various methods used to estimate uncertainties in quantum correlation functions, such as parton distribution functions (PDFs). Using a toy model of a PDF, we compare the uncertainty estimates yielded by the traditional Hessian and data resampling methods, as well as from explicitly Bayesian analyses using nested sampling or hybrid Markov chain Monte Carlo techniques. We investigate how uncertainty bands derived from neural network approaches depend on details of the network training, and how they compare to the uncertainties obtained from more traditional methods with a specific underlying parametrization. Our results show that utilizing a neural network on a simplified example of PDF data has the potential to inflate uncertainties, in part due to the cross-validation procedure that is generally used to avoid overfitting data.
Precise and accurate parton distributions are necessary to reach the physics goals of future colliders, from search for new physics to claims on non-perturbative QCD. In the last years, the CT group has expanded the concept of uncertainties in PDF analyses, in particular by including the concept of “sampling accuracy” in contrast to “fitting accuracy.” The exploration of the sampling accuracy for PDFs was linked to the tolerance criteria for Hessian-based analyses, and a dimensional-reduction technique was proposed to assess similar sources of uncertainties for Monte Carlo-based analyses. The origin of the tolerance criteria is now understood in view of the large-scale analyses. Through outside-the-fit tests, we develop on the role of parametrization in global analyses. We also extended the discussion to the comparison of pulls between various experiments in Hessian and Monte Carlo based analyses, that is necessary to leverage the use of PDF ensembles.
We present a methodology to improve the determination of PDF parametrization, the Fantômas4QCD package. It is achieved through Bézier curve fitting. Thanks to the implementation of our technique in the xFitter package, we have performed a global analysis of the pion PDF — the first analysis to account for the role of the functional form in its uncertainty.
When performing fits to data using the popular $\chi^2$ approach, uncertainty to fit parameters is determined by contours of $\Delta\chi^2=T^2$, where the tolerance $T =1 $ corresponds to the $68\%$ confidence level. PDF fits have to deal with the problem of having data sets, particularly from different experiments, that are in tension with each other. The traditional approach used by PDF fitting groups to accommodate any tension between data sets is to artificially increase the value of $T$. Here, we identify a new method of estimating the uncertainty when there is tension in the data. Specifically, we use a Gaussian Mixture Model (GMM) as a basis of our likelihood function. We demonstrate the properties and advantages of the GMM and compare it to the ad-hoc method of increasing the tolerance of $\Delta \chi^2$ in a toy model using pseudo-data.
Small-x, Diffraction and Vector Mesons
It is well known that the small x calculations for the variety of observables are characterized by large corrections at the next-to-leading order (NLO). Resummation procedure for the gluon Green's function was constructed some time ago, which takes into account correct collinear limits, through appropriate subtractions of higher order poles and shifts of the leading poles. In the present work we extend the small-x resummation procedure to the photon-gluon impact factors. We analyze the process of the virtual photon - photon scattering taking into account impact factors and gluon Green's function at NLO and perform resummation. We derive the prescription for the collinearly improved impact factors which match the NLO results. We show that such resummation prescription leads to the reduced sensitivity of the cross section on the scale choice and is also stable with respect to changes from LO to NLO improved impact factors.
The potential discovery of gluon saturation is one of the chief goals of the future Electron-Ion Collider (EIC) program. The Color Glass Condensate (CGC) is an effective field theory (EFT) to characterize this novel regime of nuclear matter. In recent years, tremendous efforts have been carried out to promote the theory and phenomenology of the CGC EFT to higher precision.
We contribute to these efforts by pursuing a comprehensive analysis of deep inelastic scattering at next-to-leading-order (NLO) within the CGC EFT. We begin by studying the one-loop corrections to this process in general small-𝑥 kinematics. We show that the differential cross-section is infrared and collinear safe, and that the rapidity factorization follows the JIMWLK renormalization group equations. By subtracting the large rapidity logarithms, we isolate and provide explicit expressions for the NLO impact factor [1].
We then specialize in back-to-back kinematics in the transverse plane where this process is sensitive to unpolarized and linearly polarized parts of the Weizsäcker-Williams (WW) gluon distribution. We isolate in the impact factor the large Sudakov double and single logarithms at finite Nc. We show that consistent rapidity and Sudakov resummation can be achieved provided that the rapidity evolution of the WW distribution is amended by a kinematic constraint that imposes lifetime ordering of successive gluon emissions. After subtracting both rapidity and Sudakov logarithms, we obtain the “genuinely” O(alpha_s) one-loop contributions to back-to-back dijets, which allows studying, for the first time, azimuthal correlations within saturation physics at full NLO accuracy [2].
We will provide preliminary numerical results for azimuthal dijet correlations at the EIC at full NLO [3].
[1] P. Caucal, F. Salazar and R. Venugopalan, JHEP 2021 (11), 1-108 18,2021
[2] P. Caucal, F. Salazar, B. Schenke and R. Venugopalan, arXiv:2208.13872 (accepted to JHEP)
[3] P. Caucal, F. Salazar, T. Stebel, B. Schenke and R. Venugopalan (work in progress).
In this talk, we will discuss the back-to-back limit of the DIS dijet production at next-to-eikonal accuracy computed in a highly boosted gluon background field within the Color Glass Condensate (CGC) framework. We will show that the various types of next-to-eikonal corrections can be written as field strength insertions on the CGC Wilson lines which provide direct relation with the gluon TMDs defined from the two-point correlators of the field strength. We will then discuss the interplay between the subeikonal corrections in the CGC and the higher twist corrections in the TMD factorization.
We examine the process of producing a quark-gluon dijet in DIS in the CGC at leading order. We have to go beyond the eikonal approximation by including quark exchanges with the target that we take to be unpolarised. We provide final expressions for the DIS cross sections including quark masses. This might be used as a leverage for experimentally tagging one heavy quark jet and one light jet. Taking the correlation limit in the final expressions, we recover the unpolarised quark TMD at low $x$ for both longitudinal and transverse photons.
We propose semi-inclusive diffractive deep inelastic scattering (SIDDIS) to investigate the gluon tomography in the nucleon and nuclei at small-x. The relevant diffractive quark and gluon parton distribution functions (DPDF) can be computed in terms of the color dipole S-matrices in the fundamental and adjoint representations, respectively.
We calculate [1] the contribution from the $q \bar q g$ state production to the diffractive cross sections in deep inelastic scattering [2,3] at high energy. The obtained cross section is finite by itself and a part of the full next-to-leading order result for the diffractive structure functions. We perform the calculation in exact kinematics in the eikonal limit, and show that the previously known high-$Q^2$ [2] and large-$M_X^2$ [4] results for the structure functions can be extracted from our results in the appropriate limits. We furthermore discuss the steps required to obtain the full next-to-leading order results for the structure functions in the Color Glass Condensate formalism, and ongoing application of these results to phenomenology.
[1] G. Beuf, H. Hänninen, T. Lappi, Y. Mulian, H. Mäntysaari, Phys.Rev.D 106 (2022) 9, 094014
[2] K.J. Golec-Biernat, M. Wusthoff, Phys.Rev.D 60 (1999)114023
[3] H. Kowalski, T. Lappi, C. Marquet, R. Venugopalan, Phys.Rev.C 78 (2008)045201
[4] Y. V. Kovchegov, E. Levin, Nucl. Phys. B 577 (2000) 221
[5] S. Munier, A. Shoshi, Phys. Rev. D 69 (2004), 074022
The gluon density has been observed to increase rapidly with energy, which would eventually violate unitarity. At high energies, however, nonlinear effects start to become important, slowing down the evolution of the gluon density and hence giving rise to gluon saturation. To study this saturation region of QCD one possibility is to look at diffractive processes, as being approximately proportional to the gluon density squared these are especially sensitive to saturation effects. It is thus important to have a precise theoretical understanding of diffractive processes, the simplest of which is the inclusive diffractive particle production that can be written in terms of the diffractive structure functions.
In this talk, we will show results from our on-going work on calculating diffractive structure functions at NLO in the dipole picture [1], where the interaction with the hadronic target is described by the Color Glass Condensate effective field theory. This calculation will complete the work done on Ref. [2] where the finite contribution for the initial-state gluon emission was calculated. In particular, we will show the cancellation of the divergences from the different Feynman diagrams in the process, along with the importance of resumming logarithmic rapidity divergences in the interaction with the target by the Balitsky-Kovchegov equation. The resulting finite expressions are in a form that is directly suitable for numerical calculations, which allows for phenomenological analyses of diffractive structure functions at NLO.
[1] T. Lappi, H. Mäntysaari, R. Paatelainen, J. Penttala, in preparation
[2] G. Beuf, H. Hänninen, T. Lappi, Y. Mulian, H. Mäntysaari, Phys.Rev.D 106 (2022) 9, 094014, arXiv: 2206.13161 [hep-ph]
In this talk, we present numerical results on diffractive dissociation of virtual photon in the scattering off hadron. The calculation employs the dipole picture of diffractive deep inelastic scattering and solutions to nonlinear Kovchegov-Levin equation, taking into account the running coupling correction and a simple treatment of impact parameter dependence. The (generalized) McLerran-Venugopalan amplitudes are chosen as the initial conditions for the nonlinear evolution, with relevant parameters being constrained by the inclusive DIS data from HERA. The results show a reasonable description to the diffractive HERA data on electron-proton collision, which demonstrates the possibility to extend the calculation to the scattering off nuclei. Some results for the latter case are then presented, which serve as predictions for the future Electron-Ion Collider.
Electroweak Physics and Beyond the Standard Model
Measurements of multiboson production at the LHC probe the electroweak gauge structure of the Standard Model for contributions for anomalous gauge couplings. Processes involving quartic gauge couplings have become experimentally accessible at the LHC. We present recent ATLAS results of vector-boson scattering in the Zgamma channel, where the Z boson decays to neutrinos producing missing transverse momentum in the event, and the same-sign WW channel, with both W bosons decaying leptonically. In addition, inclusive and differential measurements of triboson production are presented in the Zyy channel. All presented results are used to constrain dimension-eight operators affecting quartic electroweak couplings in the Effective Field Theory framework. If available, additional vector-boson scattering, as well as triboson measurements will be discussed.
Vector boson scattering is a key production process to probe the electroweak symmetry breaking of the standard model, since it involves both self-couplings of vector bosons and coupling with the Higgs boson. If the Higgs mechanism is not the sole source of electroweak symmetry breaking, the scattering amplitude deviates from the standard model prediction at high scattering energy. Moreover, deviations may be detectable even if a new physics scale is higher than the reach of direct searches. Latest measurements of production cross sections of vector boson pairs in association with two jets in proton-proton collisions at sqrt(s) = 13 TeV at the LHC are reported using a data set recorded by the CMS detector. Differential fiducial cross sections as functions of several quantities are also measured.
easurements of multiboson production at the LHC are important probes of the electroweak gauge structure of the Standard Model and give constraints on anomalous gauge boson couplings. In this talk we present recent ATLAS measurement of double-polarization in WZ events and highlight the first observation of simultaneous pair-production of longitudinally polarized vector bosons. We also show results on Zy and WW production in association with jet activity. These precise differential measurements provide inputs for QCD modelling of diboson events. Moreover, precise boson, diboson and Higgs differential cross-section measurements are interpreted in a combined Effective Field Theory analysis, allowing to systematically probe gauge boson self-interactions.
We study the potential of DIS measurements at the Large Hadron-electron Collider (LHeC) and the Electron-Ion Collider (EIC) to probe physics beyond the Standard Model. Our study is performed in the context of the Standard Model Effective Field Theory (SMEFT). We find that future measurements at both machines can improve existing SMEFT fits to precision electroweak data by resolving blind spots in fits that utilize LEP and SLC data. We further show that the LHeC can probe semi-leptonic four-fermion operators to the 10 TeV level in some cases, improving upon the LHC reach.
An overview of the latest NA62 results and the future prospect of the experiment are presented. The NA62 experiment at CERN collected the world’s largest dataset of charged kaon decays in 2016-2018, leading to the first measurement of the branching ratio of the ultra-rare $K^+ \rightarrow \pi^+ \bar\nu \nu$ decay, based on 20 candidates.
The radiative kaon decay $K^+ \rightarrow \pi^0 e^+ \nu \gamma$ (Ke3g) was studied with a data sample of O(100k) Ke3g candidates with sub-percent background contaminations recorded in 2017-2018. The most precise measurements of the branching ratio and of T-asymmetry are achieved.
An analysis of the flavour-changing neutral current $K^+ \rightarrow \pi^+ \mu^+ \mu^-$ decay, based on about 27k signal events with negligible background contamination collected in 2017 and 2018 with a dedicated pre-scaled di-muon trigger, leads to the most precise determination of the branching ratio and of the form factor.
New preliminary results are obtained from an analysis of the $K^+ \rightarrow \pi^+ \gamma \gamma$ decay using data collected in 2016-2018 with a minimum-bias trigger. The sample, about 15 times larger than the previous largest one, leads to an unprecedented sensitivity. This analysis can be naturally extended to search for the $K^+ \rightarrow a$, $a \rightarrow \gamma \gamma$ process, where a is a short-lived axion-like particle.
Dedicated trigger lines were employed to collect di-lepton final states, which allowed establishing new stringent upper limits on the rates of lepton flavour and lepton number violating kaon decays.
NA62 can also be run as a beam-dump experiment, by removing the kaon production target and moving the upstream collimators into a “closed” position. Analyses of the data taken in beam-dump mode were performed to search for visible decays of exotic mediators, with a particular emphasis on Dark Photon models.
The first observation of the decay $K^\pm \rightarrow \pi^0 \pi^0 \mu^\pm \nu$ (K00μ4) by the NA48/2 experiment at the CERN and the preliminary measurement of the branching ratio are also presented. The result is converted into a first measurement of the R form factor in Kl4 decays and compared with the prediction from 1-loop Chiral Perturbation Theory.
The electron-ion collider (EIC) will be the first collider capable of simultaneously polarizing the spin of both the leptons and hadrons involved. This opens the possibility for measurements of the nucleon spin structure and Parity-Violating (PV) asymmetry in Deep Inelastic Scattering (DIS), for the first time, at a collider setting. At the meantime, it also calls for a complete derivation of DIS inclusive scattering cross sections, given that existing formalism at Jefferson Lab omitted electroweak contribution, while that developed for high energy ep colliders (such as HERA) omitted the mass of the hadrons and rarely included the transversely polarized hadrons. In addition, the scattering between transversely polarized leptons and hadrons, with the latter either unpolarized or polarized, do not yet exist in explicit forms that can be applied to experiments in a straightforward way. In this talk, we will present the cross section calculations for DIS with both longitudinally and transversely polarized leptons and hadrons, with no approximations made, and with all three contributions – γγ,γZ,ZZ – included. With these calculations, we now have cross sections for every relevant set of polarizations for the leptons and hadrons. We will also, for the first time, provide an explicit expression for PVDIS asymmetry with transversely polarized leptons, that can be related to existing data on beam-normal single-spin asymmetry (BNSSA) measured in past PV electron scattering experiments. This will also possibly help explore new physics observables or experiments at Jefferson Lab, EIC, and elsewhere.
To describe low-energy (anti)neutrino fluxes in modern coherent elastic neutrino-nucleus scattering experiments as well as high-energy fluxes in precision-frontier projects such as the Enhanced NeUtrino BEams from kaon Tagging (ENUBET) and the Neutrinos from STORed Muons (nuSTORM), we evaluate (anti)neutrino energy spectra from radiative muon, pion, and kaon decays at O($\alpha$) level and quantify corresponding uncertainties. We discuss the corresponding changes to fluxes and neutrino-nucleus cross sections.
Inverse muon decay is a promising tool to constrain neutrino fluxes with energies $ E_\nu \ge 10.9~\mathrm{GeV}$. To provide precise theory predictions for this process, we generalize the framework of radiative corrections in muon decay to the scattering reactions $\nu_\mu e^- \to \nu_e \mu^-$ and $\bar{\nu}_e e^- \to \bar{\nu}_\mu \mu^-$ and present resulting cross sections and energy spectra. We discuss how radiative corrections modify experimentally interesting distributions in MINERvA and future DUNE experiments.
In the high energy heavy ion collisions the ions can act as intense sources of electromagnetic radiation, or in the language of particle physics, photon-photon collisions. This is in particular the case for so--called ultraperipheral collisions (UPCs), where the impact parameter separation of the ions is significantly larger than the range of QCD, with the ions remaining intact after the collision. This production mechanism is a key ingredient in the LHC precision and discovery programme, providing a unique probe of physics within and beyond the Standard Model. However, in order to facilitate this, a precise theoretical treatment of the underlying process is mandatory. In this talk I will present an update to the SuperChic Monte Carlo generator, which provides such a treatment. A full account of mutual ion--ion electromagnetic dissociation is now in particular provided, including its full kinematic dependence. This dissociation is rather common in UPCs, and indeed can be measured in the collider with dedicated zero degree calorimeter (ZDC) detectors. Moreover, it will in general modify the predicted kinematic distributions in the central detector, as well as the cross section. I will compare to recent data from the LHC and RHIC, and discuss the outlook for the future.
QCD with Heavy Flavours and Hadronic Final States
The CLAS Collaboration presents a measurement of the nuclear dependence of di-hadron production in deep inelastic scattering off nuclei using the CLAS detector at Jefferson Lab. We report the first measurement of azimuthal correlations in nuclear DIS, and their dependence on kinematic variables such as rapidity separation and the transverse momenta of the two pions. We observe that the distribution of the azimuthal separation between pions peaks at $\pi$, but this peak becomes wider and shorter for heavier nuclei compared to deuterium, indicating a "broadening" of the correlations. This represents a new type of study in electron-nucleus collisions and serves as a pathfinder for future experiments with CLAS12 and the Electron-Ion Collider.
Mass-dependent quark contributions are of great importance to DIS processes. The simplified-ACOT-$\chi$ scheme includes these effects over a wide range of momentum transfers up to next-to-leading order in QCD. In recent years an improvement in the case of neutral current DIS has been achieved by using zero-mass contributions up to next-to-next-to-leading order (NNLO) with massive phase-space constraints. In this talk, we extend this approach to the case of charged current DIS and provide an implementation in the open-source code APFEL++
. The increased precision will be valuable for ongoing and future neutrino programs, the Electron-Ion-Collider and the studies of partonic substructure of hadrons and nuclei. A highly efficient implementation using gridding techniques extends the applicability of the code to the determination of parton distribution functions (PDFs).
Heavy quarkonium production of high transverse momentum ($p_T$) in hadronic collisions can be studied in the QCD factorization formalism in both leading and the first subleading power in $1/p_T$ expansion with heavy quarkonium fragmentation functions (FFs) [1]. The scale evolution of quarkonium FFs enables us to resum logarithmically enhanced corrections $\alpha_s\ln(p_T^2/m^2)$ with heavy quark mass $m$, which is an essential piece to explore the nonperturbative process of bound quarkonium formation. Boundary conditions of the evolution equations of the FFs at $p_T\sim 2m$ are given by combining perturbatively calculable coefficients in NRQCD and long-distance-matrix elements (LDMEs) for different intermediate states of a produced heavy quark pair. LDMEs correspond to relative weights of individual terms after expanding the input FFs in quark velocity $v$, and should be determined by data fitting.
We demonstrated in Ref.[1] that the QCD contribution to the production at the first subleading power is critically important for describing the full range of $p_T$-distributions of J/$\psi$ production at the hadron colliders, in particular, for the region of $p_T \ge {\cal O}(2m)$, while the leading power contribution describes the main feature of data for $p_T\gg {\cal O}(2m)$. In this talk, we will present our predictions for transverse momentum distribution of J$/\psi$ production in lepton-hadron scatterings at the EIC in terms of a hybrid factorization approach to take into account both collision-induced QCD and QED radiative corrections on equal footing [2]. At the EIC energy, we will demonstrate that the first subleading power contribution is very important for matching our calculations with the resummation of the logarithms to the fixed-order NRQCD calculations at $p_T\sim {\cal O}(2m)$. We will discuss the complementarity between inclusive high-$p_T$ J/$\psi$ production without measuring the scattered electron and the production of J/$\psi$ in semi-inclusive deep inelastic scattering (SIDIS) with the scattered electron measured. We will also discuss the transition from the collinear factorization regime to the phase-space where TMD factorization is necessary.
[1] K. Lee, J.W.Qiu, G. Sterman and K.Watanabe,
``Subleading power corrections to heavy quarkonium production in QCD factorization approach,'' [arXiv:2211.12648 [hep-ph]].
[2] T. Liu, W. Melnitchouk, J.W. Qiu and N. Sato,
``A new approach to semi-inclusive deep-inelastic scattering with QED and QCD factorization,'' JHEP 11, 157 (2021) [arXiv:2108.13371 [hep-ph]].
Centrality-dependent data of hadron and jet attenuation in deep inelastic scattering (DIS) on nuclei can shed new light on the physics of final-state interactions in nuclear matter, including the path-length dependence of in-medium parton shower evolution. Thus-far, such measurements that can disentangle shadowing and energy loss effects on semi-inclusive DIS cross sections have not been performed. Recent simulation studies, based on the BeAGEL Monte Carlo event generator have demonstrated the feasibility of experimental centrality determination in electron nucleus (e-A) reactions at the electron-ion collider (EIC). Motivated by this result, we present the first theoretical investigation of hadron and jet cross section modification in central and peripheral e-Pb collisions. We find that the variation in the magnitude of the semi-inclusive cross section suppression as a function of centrality is less than a factor of two. In more differential distributions, such as the hadron spectra as a function of the hadronization fraction $z_h$, the difference can be enhanced up to an order of magnitude. We discuss the connection of our calculations to the proton-nucleus (p-A) cold nuclear matter program.
The lepton-jet momentum imbalance in deep inelastic scattering events offers a useful set of observables for unifying collinear and transverse-momentum-dependent frameworks for describing high energy Quantum Chromodynamics (QCD) interactions. The imbalance in the laboratory frame was measured recently [1] using positron-proton collisions from HERA Run II. With a new machine learning method, the measurement was performed simultaneously and unbinned in eight dimensions, however the results were projected onto four key observables. This paper extends over those results by showing the multi-differential nature of the unfolded result. In particular, the lepton-jet correlation observables are measured differentially in kinematic properties of the scattering process, the momentum transfer $Q^2>150$ GeV$^2$ and inelasticity $0.2
[1] PRL 128 (2022) 123003
At leading order in positron-proton collisions, a lepton scatters off a quark through virtual photon exchange, producing a quark jet and scattered lepton in the final state. The total transverse momentum of the system is typically small, however deviations from zero can be attributed to perturbative initial and final state radiations in the form of soft gluon radiation when the transverse momentum difference, $\vert\vec{P}_{\perp}\vert$, is much greater than the total transverse momentum of the system, $\vert\vec{q}_{\perp}\vert$. The soft gluon radiation comes only from the jet, and should result in a measurable azimuthal asymmetry between $\vec{P}_{\perp}$ and $\vec{q}_{\perp}$. Quantifying the contribution of soft gluon radiation to this asymmetry should serve as a novel test of perturbative QCD as well as an important background estimation for measurements of the lepton-jet imbalance that have recently garnered intense investigation. The measurement is performed in positron-proton collisions from HERA Run II measured with the H1 detector. A new machine learning method is used to unfold eight observables simultaneously and unbinned. The final measurement, the azimuthal angular asymmetry, is then derived from these unfolded and unbinned observables. Results are compared with parton shower Monte Carlo predictions as well as soft gluon radiation calculations from a Transverse Momentum Dependent (TMD) factorization framework.
The radiation pattern within high energy quark and gluon jets (jet substructure) is used extensively as a precision probe of the strong force as well as an environment for optimizing event generators for nearly all tasks in high energy particle and nuclear physics. While there has been major advances in studying jet substructure at hadron colliders, the precision achievable by collisions involving electrons is superior, as most of the complications from hadron colliders are absent. Therefore jets are analyzed which were produced in deep inelastic scattering events and recorded by the H1 detector. This measurement is unbinned and multi-dimensional, making use of machine learning to correct for detector effects. Results are presented after unfolding the data to particle level for events in the fiducial volume of momentum transfer $Q^2>150$ GeV$^2$, inelasiticity $0.2< y < 0.7$, jet transverse momentum $p_{T,jet}>10$ GeV, and jet pseudorapidity $-1<\eta_{jet}<2.5$. The jet substructure is analyzed in the form of generalized angularites, and is presented in bins of $Q^2$ and $y$. All of the available object information in the events is used to achieve the best precision through the use of graph neural networks. Training these networks was enabled by the new Perlmutter supercomputer at Berkeley Lab that has a large number of Graphical Processing Units (GPUs). The data are compared with a broad variety of predictions to illustrate the versatility of the results for downstream analyses.
We perform a renormalization group (RG) analysis of cold nuclear matter effect on hadron production in semi-inclusive DIS. We focus on the asymptotic limit where the ratio $t = E/(\mu_D^2 L)\rightarrow \infty$, with $E$, $L$, $\mu_D$ being the energy of the jet, the nuclear size, and the inverse interaction range in cold nuclear matter, while the opacity of the medium remains at order unity. We demonstrate that one can resum the leading $\ln t$ enhanced medium effects by a set of coupled differential RG evolution equations, which accounts for strongly formation-time ordered emissions from the endpoint regions of the medium-induced parton splitting functions. Using this new analytic framework, we obtain a good description of the medium-modified pion production in e-A collisions as measured by the HERMES experiment and present predictions for kinematics relevant for the future EIC. Finally, we discuss its connection to the widely used modified DGLAP evolution approach and implications for the development of the Monte-Carlo event generator for e-A collisions.
General-purpose event generators such as Pythia are programs that model complete particle interactions, including the hard process, parton showers, multiparton interactions, hadronization, etc. The objective of these generators is to provide state-of-the-art predictions for high energy collisions, and are essential for bridging the gap between theoretical models and experimental data. Pythia also includes the Angantyr framework for heavy ion collisions.
Pythia offers an accurate simulation of photon-proton collisions validated agains photoproduction data from HERA. In our current work, we take the first steps towards extending this to photon-ion collisions, which are essential for EIC physics. We treat the photon wavefunction as consisting of three components: the direct part, the vector meson dominance (VMD) part, and the anomalous part. For collisions in the VMD state, the interaction can be treated as a hadron-ion interaction, and this is what we have achieved in our current goal applying linear combination of different vector-meson states. We compare this new approach to the full photoproduction in photon-proton, and show results for how the interactions are modified by nuclear effects with in Angantyr. We consider also ultra-peripheral heavy-ion collisions and compare our results of multiplicity distribution and transverse momentum spectra to recent ATLAS photon-ion data.
Spin and 3D Structure
Measurements of the longitudinal double-spin asymmetry, $A_{LL}$, by the STAR experiment have contributed significantly to our understanding of the gluon helicity distribution, $\Delta g(x)$, inside the proton. Results from the 2009 inclusive jet measurement, when included into global analyses, indicated substantial positive polarization for gluons with partonic momentum fraction $x$ greater than 0.05. In addition to the inclusive jets, analyses of dijet production extending to higher pseudorapidity (up to $\eta \sim 1.8$) provide better constraints on the $x$ dependent behavior of $\Delta g(x)$. Recently, STAR published several new results at midrapidity (up to $\eta \sim 1.0$) using the $p+p$ data collected in 2012, 2013 and 2015 at both $\sqrt{s}$ = 510 and 200 GeV. These new results confirm the previous findings and provide additional constraints in the largely unexplored region of $x < 0.05$. In this talk, the preliminary results of the $A_{LL}$ for dijet production at intermediate pseudorapidity (up to $\eta \sim 1.8$) based on 2015 data, with twice the figure-of-merit of the 2009 data, will be presented. This result will be compared with the published ones, and its potential impact on $\Delta g(x)$ will be discussed.
The spin physics program at the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) remains an essential tool in illuminating the internal spin structure of the proton. One major emphasis of the program is the measurement of longitudinal double spin asymmetries $(A_{LL})$ in a number of different final states from collisions of longitudinally polarized protons $(\vec{p} + \vec{p})$. Recent measurements of direct photon, jet, and charged pion spin asymmetries from $\vec{p} + \vec{p}$ access gluon polarization to leading order, something not possible with related lepton-hadron scattering measurements. Alongside the spin asymmetries, corresponding cross sections of direct photons, jets, and various identified hadrons have also been measured. These cross section measurements and their ratios can help to constrain fragmentation functions as well as unpolarized parton distribution functions. In this talk, I will present these recent results and the status of other ongoing spin analyses from PHENIX.
One of the primary goals of the RHIC spin program is to determine the polarized gluon distribution
function, $\Delta g$, within the proton. At the leading order, proton-proton collisions involve a mixture of
quark-quark, quark-gluon, and gluon-gluon scatterings. At RHIC kinematics, the quark-gluon
and gluon-gluon contributions dominate, which makes RHIC an ideal tool to study $\Delta g$.
The STAR Collaboration has recently published measurements of the longitudinal double-spin
asymmetry, $A_{LL}$, for inclusive jet and dijet
production at midrapidity in polarized proton-proton collisions at a center-of-mass energy of $\sqrt{s}=510\,$GeV,
based on the high luminosity data sample collected by the STAR experiment in 2013. These measurements
complement and improve the precision of previous STAR measurements at the same center-of-mass energy
that probe the polarized gluon distribution function within the partonic momentum fraction range of $0.015 < x < 0.25$.
The dijet asymmetries are separated into four jet-pair topologies and measured with good precision at low dijet invariant mass, which
provide further constraints on the $x$
dependence of the polarized gluon distribution function.
These recently published midrapidity $A_{LL}$ results will be presented and compared to previous measurements, along with
comparisons to current next-to-leading-order global analyses.
Using the spectral representation of the quark propagator we study the Dirac decomposition of the gauge invariant quark propagator, whose imaginary part describes the hadronization of a quark as this interacts with the vacuum.
In light-like axial gauge, we obtain a new sum rule for the spectral function associated to the gauge fixing vector. We then demonstrate the formal gauge invariance of the so-called jet mass, that can be expressed in any gauge as the first moment of the chiral-odd quark spectral function. We also present a gauge-dependent formula that connects the second moment of the chiral-even quark spectral function to invariant mass generation and final state rescattering in the hadronization of a quark.
We finally discuss how the jet mass contributes to and can be measured in inclusive DIS and electron-positron collisions.
In the 1970's, Fermilab discovered that $\Lambda$ hyperons are polarized in collisions of unpolarized protons on beryllium. This discovery initiated a 50 year long series of measurements which aimed at solving this $\Lambda$ hyperon polarization puzzle. Although this puzzle remains to be an open question, the self-polarizing feature of $\Lambda$ hyperon has been providing an important experimental handle on measuring other polarization phenomena in nonperturbative Quantum Chromodynamics, e.g., the global $\Lambda$ hyperon polarization in heavy-ion collisions, spin transfer in polarized p$+$p collisions, etc. Hereby we present a status on the first measurement of spin correlation between two $\Lambda$ hyperons, including $\Lambda\Lambda$, $\bar{\Lambda}\bar{\Lambda}$, and $\Lambda\bar{\Lambda}$, in p$+$p collisions at $\sqrt{s}=200$ GeV and $\sqrt{s}=510$ GeV using the STAR detector. The spin correlation of two $\Lambda$ hyperons is measured with respect to each other on an event-by-event basis, contrary to other established $\Lambda$ hyperon polarization measurements. This new observable can provide further insights to the origin of the $\Lambda$ hyperon polarization, e.g., the interplay between the initial-state parton spin and the final-state polarising fragmentation. In addition, the spin correlation between a $\Lambda\bar{\Lambda}$ pair can provide a first Clauser-Horne-Shimony-Holt (CHSH) inequality test for spin entanglement in high-energy hadron collider experiment. Implication of the CHSH inequality test in the context of high-energy hadron collisions will be discussed.
Transverse Λ (uds) polarization observed over four decades ago contradicted expectations from early leading-order perturbative QCD calculations. Recent studies have linked the polarization to the process of hadronization, where hyperon polarization from unpolarized proton-proton and proton-nucleus collisions comes from either including higher-order twist-3 collinear multi-parton correlation matrix elements or convolution of a twist-2 transverse-momentum-dependent parton distribution function with a transverse-momentum-dependent fragmentation function. Measurements of hyperon polarization from unpolarized pp, pPb, and Pbp collisions, along with e+e− and semi-inclusive deep-inelastic scattering measurements can advance our understanding of this effect in QCD. The high energy of the LHC, which produces hyperons in abundance,and the coverage and precision measurement possibilities from LHCb’s forward geometry will be ideal to study polarization of hyperons as a function of both pT and xF . The status of Λ and ̄Λ polarization measurements performed for pPb and Pbp collisions, √sN N = 5.02 TeV, at LHCb will be presented.
Spin dependent quark and gluon distributions can lead to distinctive features in the angular dependances and asymmetries of pp and ep scattering processes. Of particular interest are heavy quark production processes, wherein spin asymmetries of the heavy quarks, correlated with diquarks, adumbrate the underlying spin dependances. Heavy flavor hyperons with diquark spectators as well as top quark decay polarization asymmetries connect to the underlying perturbative and non-perturbative QCD dynamics.
Using the self-analyzing decay of the $\Lambda$, the longitudinal spin transfer $D_{LL'}$ to the hyperon from a polarized electron beam scattering off an unpolarized proton target can be determined. For $\Lambda$s produced in the current fragmentation region, this quantity is proportional to the helicity dependent fragmentation function $G_1^\Lambda$ and can provide insight into the spin structure of the $\Lambda$. Currently, limited experimental data on $D_{LL'}$ cannot discriminate between different models of $\Lambda$ spin structure. This contribution reports on the measurement of the longitudinal spin transfer using data taken by the CLAS12 spectrometer at Jefferson Lab with a 10.6 GeV polarized electron beam. We also report on status of the ongoing analysis of spin transfer and back-to-back hadron correlations with target fragmentation $\Lambda$s.
The axial-vector form factors of the light, singly and doubly charmed baryons are investigated in the framework of $SU(4)$ chiral constituent quark model. The axial-vector form factors having physical significance correspond to the generators of the $SU(4)$ group with flavor singlet $\lambda^0$, flavor isovector $\lambda^3$, flavor hypercharge $\lambda^8$ and flavor charmed $\lambda^{15}$ combinations of axial-vector current at zero momentum transfer. In order to further understand the $Q^2$ dependence of these charges, we have used the conventionally established dipole form of parametrization.
The mechanism of the nuclear modifications of parton densities at $x > 0.3$ (EMC effect) observed in DIS experiments remains a major open question in QCD. In inclusive nuclear DIS, $e + A \rightarrow e’ + X$, one observes only the average effect but cannot learn anything about the underlying nuclear interactions. In DIS on the deuteron with spectator nucleon tagging, $e + D \rightarrow e’ + X + p(n)$, the nuclear configuration is fixed by the detected spectator momentum, and one can analyze the nuclear modifications differentially in the relative momentum/distance between the nucleons. We study the feasibility of measuring the configuration-dependent EMC effect in deuteron DIS with spectator tagging at the EIC. The BeAGLE event generator is supplied with a general virtuality-dependent parametrization of the tagged EMC effect constrained by theory and inclusive nuclear DIS data. Proton and neutron spectator tagging is simulated with the baseline EIC far-forward detector (extending earlier results reported in [1]). An analysis strategy for the tagged EMC effect is outlined (ratio observables, separation of initial- and final-state effects), and the uncertainties and impact of the measurements are quantified.
[1] A Jentsch, Zh. Tu, C. Weiss, Phys.Rev.C 104 (2021) 6, 065205
I will present a new interpretation of the deviations of the nuclear deep inelastic structure function from the free nucleon one, known as the nuclear EMC effect, based on the non locality of the hard scattering off the bound nucleon. Because of the extended size of the hard probe-quark interaction region, final state interactions between the struck parton and the bound nucleon remnants are not suppressed
but generate a term proportional to the moment of a transverse momentum distribution.
The size of this contribution is regulated by the amount of nucleon transverse momentum which is enhanced when nucleon short range correlations are taken into account.
Prospects for inclusive physics studies at the Electron-Ion Collider (EIC) using the EPIC detector are explored. EPIC is currently under rapid development and is expected to be operational from the first day of data taking. Simulations are used to determine the detector acceptance and resolutions, and to estimate some significant sources of systematic uncertainty such as backgrounds and inefficiencies in electron identification. Expected luminosities and beam polarizations in ep and eA collisions allow projections of the EPIC detector performance into measurements of charged- and neutral-current cross sections and asymmetries. The impact of these measurements on derived quantities such as polarized and unpolarized parton distribution functions is evaluated.
A precise reconstruction of the kinematic variables $x$, $y$ and $Q^2$ is essential for the physics program at the future EIC. Conventional reconstruction methods usually rely on two of the four measured quantities (energy and angle of the scattered electron and hadronic final state) with the resolution of each method depending on the kinematic regime under study, detector performance, and initial-state photon radiation. A kinematic fit using all measured quantities can fully exploit the available information to obtain a best estimate of the kinematic variables, as well as the energy of any initial state radiation. A technique applying a Bayesian method with suitable priors has been applied to fully simulated inclusive neutral current EIC data in the context of the planned EPIC detector. The performance of the kinematic fitting method is compared with conventional methods. The impact of the precise kinematic reconstruction on the expected physics output of the experiment is explored.
In this talk, we explore machine learning-based jet and event identification at the future Electron-Ion Collider (EIC). We study the effectiveness of machine learning-based classifiers at relatively low EIC energies, focusing on (i) identifying the flavor of the jet and (ii) identifying the underlying hard process of the event. We propose applications of our machine learning-based jet identification in the key research areas at the future EIC and current Relativistic Heavy Ion Collider program, including enhancing constraints on (transverse momentum dependent) parton distribution functions, improving experimental access to transverse spin asymmetries, studying photon structure, and quantifying the modification of hadrons and jets in the cold nuclear matter environment in electron-nucleus collisions. We establish first benchmarks and contrast the estimated performance of flavor tagging at the EIC with that at the Large Hadron Collider. We perform studies relevant to aspects of detector design including particle identification, charge information, and minimum transverse momentum capabilities. Additionally, we study the impact of using full event information instead of using only information associated with the identified jet. These methods can be deployed either on suitably accurate Monte Carlo event generators, or, for several applications, directly on experimental data. We provide an outlook for ultimately connecting these machine learning-based methods with first principles calculations in quantum chromodynamics.
[1] Lee, Mulligan, Ploskon, Ringer, Yuan. arXiv:2210.06450.
Electron scattering data off protons from the CLAS12 detector in Hall B at Jefferson Laboratory have become available and cover a wide kinematic range in W up to 2.5 GeV and Q2 up to 9 GeV2, offering new opportunities to explore inclusive, semi-inclusive, and fully exclusive reactions. A study that aims to extract the inclusive electroproduction cross sections from the CLAS12 data collected at a beam energy of 10.6 GeV from an unpolarized liquid-hydrogen target is now almost finished and preliminary results will be presented. Because of the large acceptance of CLAS12, these data offer a unique opportunity to measure inclusive cross sections at W from the meson electroproduction threshold to 2.5 GeV within any given Q2-bin from 2.5 to 9 GeV2. This unique W- coverage at fixed Q2-values is of particular importance for the extension of our knowledge on the nucleon parton distribution function from the data on F2 structure function in the resonance region by employing the existing CLAS results on the γpN* electroexcitation amplitudes. These studies also offer valuable input for the exploration of quark-hadron duality.
Charge symmetry of the nucleon has been critically important in understanding the partonic structure of nuclei because halves the number of quark PDFs -- $u^p(x) = d^n(x)$ and $u^n(x) = d^p(x)$. Going back to the charge independence of the nuclear force, this symmetry is well founded, however, there are known sources of charge symmetry violation (CSV) such as the quark masses and electromagnetic coupling. We report on a measurement of pion electroproduction in semi-inclusive deep-inelastic scattering on hydrogen and deuterium targets. The experiment was conducted at Jefferson Lab in Hall C in the winter of 2019 and measured the charged pion SIDIS cross section ratio of $\sigma(\pi^-)/\sigma(\pi^+)$ for $0.3 < z < 0.75$, $3.0 < Q^2 < 5.0$ GeV$^2$, and $0.3 < x < 0.6$. We extract the charge symmetry violating parton distribution in the valence region and the ratio of favored to unfavored fragmentation functions. We will discuss the results of CSV in the valence parton distributions and emphasize the need for a global analysis which includes charge symmetry violation.
An important physics program at the JLAB12 and EIC facilities is understanding the emergence of the masses and internal structures of Goldstone mesons, pion and kaon, through measurements of their electromagnetic form factors at large momenta transfers, $Q$. In this talk we will present first results of pion and kaon electromagnetic form factors up to $Q^2=10$ GeV$^2$ and $Q^2=30$ GeV$^2$, respectively, from state-of-the-art lattice QCD calculations at the physical values of pion and kaon masses. For a deeper understanding, we will compare these results with the predictions based on pion and kaon distribution amplitudes and charge radii, both obtained from lattice QCD calculations with the same setup. These results not only provide discriminatory tests for QCD-inspired models but also serve as benchmark QCD predictions for measurements at JLAB12 and EIC.
abstract attached
The high-x data from the ZEUS Collaboration are used to extract parton density distributions of the proton deep in the perturbative regime of QCD. The data primarily constrain the up-quark valence distribution and new results are presented on its x-dependence as well as on the momentum carried by the up-quark. The results were obtained using Bayesian analysis methods which can serve as a model for future parton density extractions.
We discuss the preliminary results of the new global nCTEQ23 nuclear PDF analysis, combining a number of our previous analyses into one consistent framework with updates to the underlying theoretical treatment as well as the addition of new available data. In particular, the nCTEQ23 global release will be the first nCTEQ release containing neutrino DIS scattering data in a consistent manner together with JLab high-x DIS data and new LHC p-Pb data. These additions will allow to improve the data-driven description of nuclear PDFs in new regions such as the gluon for very low-x or the nuclear strange quark PDF.
We present the new CJ22 global QCD analysis of unpolarized parton distributions The work focuses on the light antiquark sea to incorporate constraints from recent SeaQuest and STAR electroweak boson production data. We make use of a more flexible antiquark imbalance parametrization than in the CJ15 analysis, that in turn is sensitive to mid-rapidity correlations between the $\bar d / \bar u$ and $d/u$ ratios in the Drell-Yan $pp/pd$ cross section measurements. As a result, the $d/u$ ratio is suppressed at large $x$ compared to the CJ15 result, and extrapolates to a substantially smaller value than obtained there as $x \to 1$.
Extractions of the structure functions from inclusive h(e,e′) and d(e, e′) reactions are important for the study of nucleon structure. Such extractions help with constraining the PDF (specially at large Bjorken X), facilitate the studies of Quark Hadron Duality and are important for non-singlet moments calculation as a test of LQCD and many more. Experiment E12-10-002 ran in Hall C at JLab in spring 2018 with a focus on measuring the precession cross sections on h and d for F2 structure functions extraction. Our measurements cover a large kinematic range in X from 0.2 to 1.0, and in Q^2 from 4 to 16 GeV^2.
I will show the results of h(e, e′), d(e, e′) cross sections and F2 structure functions, in the context of exploring the quark-hadron duality with a new method.
The precision-level reached at collider experiments offer us the unique opportunity to probe the inner structure of the protons and heavy nuclei, described in the language of parton density functions (PDFs), at an unprecedented accuracy. Despite that current determination of the proton PDFs account for nuclear effects and reciprocally the determination of the nuclear PDFs (nPDFs) depend on the proton PDFs, so far a concurrent extraction of both is not available. For the first time, we present a unified framework in which we simultaneously determine the PDFs of the proton, deuterium, and heavier nuclei up to lead. Our approach is based on the integration of the fitting framework underlying the nNNPDF3.0 determination of nuclear PDFs into that adopted for the NNPDF4.0 global analysis of proton PDFs. We benchmark in detail the performance of this integrated (n)PDF fitting framework and explore some of its phenomenological implications. Our framework represent a stepping stone towards a full integrated global analysis of non-perturbative QCD, a key ingredient for the exploitation of the scientific potential of future facilities such as the Electron-Ion Collider (EIC).
Small-x, Diffraction and Vector Mesons
Measurement of near threshold quarkonia photoproduction cross section provides a unique tool to probe gluonic structure inside the nucleon, hence allowing extraction of gluonic form factors and mass radii. $J/\Psi$-007 experiment (E12-16-007) was conducted at Hall-C of the Thomas Jefferson National Accelerator Facility to measure near threshold 2-D differential $J/\Psi$ photoproduction cross section as a function of photon energy $E_{\gamma}$ and Mandelstam variable $t$ (momentum transfer from initial photon to the produced $J/\Psi$). The experiment utilized a high intensity real photon beam produced by incidence of a 10.6 GeV incident electron beam on a copper radiator situated upstream of a hydrogen target. The produced e$^-$e$^+$ ($\mu^-\mu^+$) pair from decay of $J/\Psi$ was detected using two arm spectrometers in Hall C: the HMS and the SHMS. The scanned photon energy range $E_{\gamma}$ and momentum transfer $|t|$, are between 9.1 GeV and 10.6 GeV and up to 4.5 GeV$^2$, respectively. Recent results from analysis of the measured 2-D $J/\Psi$ photoproduction cross section (e$^-$e$^+$ channel) will be presented. In addition,
preliminary results from analysis of muon channel will be also be shown.
Exclusive charmonium photoproduction near threshold opens the door for studying the gluonic properties of the proton: gluonic GPDs, anomalous contribution to the mass of the proton, gravitational form factors, the mass radius of the proton. However, such an ambitious program requires precise measurements to validate the theoretical assumptions that relate the experimental results to the above quantities. The first total cross-section measurements of near-threshold exclusive $J/\psi $ photoproduction ($\gamma p \rightarrow J/\psi p$) by the GlueX collaboration sparked remarkable theoretical interest, however had limitted statistics. We will report new total cross-section results based on more than a four-fold increase in statistics. Even more, due to the full acceptance of the GlueX experiment for this reaction, we will present first measurements of the differential cross-sections over the whole near-threshold kinematic region. Such measurements enable more general conclusions about the reaction mechanism when compared to a wide range of theoretical predictions including GPD calculations and models with open-charm intermediate states.
When beginning to describe the structure of $^4$He, one often begins by invoking a description based on nucleon degrees of freedom -- a bound system with two protons and two neutrons -- leaving the partonic description at the level of each nucleon aside. However, the ultimate goal to understand $^4$He within Quantum Chromodynamics (QCD)k is to connect its intrisic properties with the fundamental degrees of freedom of QCD, quarks and gluons. $^4$He is a deeply bound spin-0 system and has only one chiral-even generalized parton distribution. Starting with a partonic description of the $^4$He nucleus, we can use deeply virtual Compton scattering (DVCS) to probe the quark transverse spacial distribution and also leverage deeply virtual meson production as an effective probe of the transverse gluon spacial distribution. Using the CLAS12 spectrometer at Jefferson Lab's Hall-B and a low energy recoil tracker (ALERT) to detect the recoiling $^4$He system, we will measure the coherent DVCS beam spin asymmetry and the coherent $\phi$ production cross section. We will discuss this opportunity for this experiment to study the quark and gluon structure of light nuclei and as a preview of physics anticipated at the Electron-Ion Collider.
for SoLID Collaboration
The proposed Solenoidal Large Intensity Device (SoLID) in Hall A at Jefferson Lab, will fully utilize the great physics potential of the 12-GeV energy upgrade by combining high luminosities and large acceptance to explore physics needs large statistics. We plan a common
setup to measure JPsi production near threshold, timeline compton scattering and double deeply virtual compton scattering at the same time. They will be high-precision measurements in a wide kinematical region.
This work is supported in part by U.S. Department of Energy under contract number DE-FG02-03ER41231.
One of the golden measurements at the Electron-Ion Collider (EIC) is to measure the coherent diffractive Vector Meson (VM) production on a heavy-nucleus target. The measurement is expected to be sensitive to the non-linear gluon dynamics - saturation, and most importantly, it also provides the gluon density distribution of the nucleus. While the measurement was proposed in the EIC White Paper 10 years ago, it is not until recently that the experimental challenges of this measurement were realized. In this talk, I will give an overview on the experimental developments from the EIC detector proposals on this measurement, particularly with the lessons learned. I will discuss the key challenges and future opportunities for development, e.g., incoherent production background, energy resolution of EMCal, etc. Based on a new single-stack software package in EPIC, full simulation results with the most up-to-date detector configuration will be presented.
Electroweak Physics and Beyond the Standard Model
We present here the most recent $BABAR$ results on searches for new particles with masses below the electroweak scale predicted by many extensions of the Standard Model (SM). The results are based on the full data set of about 470 $\text{fb}^{-1}$ collected at the $\Upsilon(4S)$ resonance at the PEP-II collider, including a search for an Axion-Like Particle, $a$, produced in the Flavor-Changing Neutral-Current decay $B\to K a$, with $a\to \gamma\gamma$, which is expected to be competitive with the corresponding SM electroweak processes.
We present also the search for the decays $B^{0}\to\psi_{D} + {\cal B}$ where $\cal{B}$ is a baryon ($\Lambda$ or proton), which produces the dark matter particle $\psi_{D}$ and baryogenesis simultaneously. The hadronic recoil method has been applied with one of the $B$ mesons from $\Upsilon(4S)$ decay fully reconstructed and only one baryon present in the signal $B$-meson side. The missing mass of signal $B$ meson is considered as the mass of the dark particle $\psi_{D}$. Stringent upper limits on the decay branching fraction are derived in the enrgy region between 0.5 and 4.2 GeV/c$^2$.
New light resonances are a generic signature of models of new phenomena beyond the Standard Model. The diphoton final states provides a clean final state and provides sensitivity to a wide class of such signals, in particular axion-like particles (ALPs). Several results of several such searches, both inclusive and in association with other particles, will be presented.
Lorentz and CPT symmetry in the quark sector of the Standard Model are studied in the context of an effective field theory using ZEUS ep data. Symmetry-violating effects can lead to time-dependent oscillations of otherwise time-independent observables, including scattering cross sections. An analysis using five years of inclusive neutral-current deep inelastic scattering events corresponding to an integrated luminosity of 372 pb-1 at sqrt(s) = 318 Gev has been performed. No evidence for oscillations in sidereal time has been observed within statistical and systematic uncertainties. Constraints, most for the first time, are placed on 42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd dimension-five spin-independent modifications to the propagation and interaction of light quarks.
Many new physics models predict the existence of resonances decaying into two bosons (W, Z, photon, or Higgs bosons) making these important signatures in the search for new physics. Searches for Vy, VV, and VH resonances have been performed in various final states. In some of these searches, jet substructure techniques are used to disentangle the hadronic decay products in highly boosted configurations. This talk summarises recent ATLAS searches with Run 2 data collected at the LHC and explains the experimental methods used, including vector- and Higgs-boson-tagging techniques.
Various theories beyond the Standard Model predict new, long-lived particles with unique signatures which are difficult to reconstruct and for which estimating the background rates is also a challenge. Signatures from displaced and/or delayed decays anywhere from the inner detector to the muon spectrometer, as well as those of new particles with fractional or multiple values of the charge of the electron or high mass stable charged particles are all examples of experimentally demanding signatures. The talk will focus on the most recent results using 13 TeV pp collision data collected by the ATLAS detector.
Leptoquarks are predicted by many new physics theories to describe the similarities between the lepton and quark sectors of the Standard Model and offer an attractive potential explanation for the B-physics anomalies observed at LHCb and flavour factories. The ATLAS experiment has a broad program of direct searches for leptoquarks, coupling to the first-, second- or third-generation particles. This talk will present the most recent 13 TeV results on the searches for leptoquarks with the ATLAS detector, covering flavour-diagonal and cross-generational final states.
Search for the lepton flavor violation and test of the lepton flavor universality are of great interest as a signature of the New Physics. Such decays can be searched using large amount of B and Upsilon mesons produced at Belle. We present our search for $B, B_s \to \ell\tau$, $B \to K\tau\ell$, $\Upsilon(nS) \to \ell\tau$. We also present our study on decays relevant to Lepton Flavor Universality. All these results are based on data collected by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider.
In recent years, discrepancies from standard-model predictions, which suggest violation of lepton-flavor universality, have emerged in multiple measurements of B meson decays. This talk reports on related, recent Belle II results on lepton-flavour universality and long-lived particles.
With the pp collision dataset collected at 13 TeV, detailed measurements of Higgs boson properties can be performed. The Higgs kinematic properties can be measured with increasing granularity, and interpreted to constrain beyond-the-Standard-Model phenomena. This talk presents the measurements of Higgs boson differential and fiducial cross sections with various decay modes, as well as their combination and interpretations.
QCD with Heavy Flavours and Hadronic Final States
Understanding the detailed structure of energy flow within jets, a field known as jet substructure, plays a central role in searches for new physics, and precision studies of QCD. Many applications of jet substructure require an understanding of jets initiated by heavy quarks, whose description has lagged behind remarkable recent progress for massless jets.
In this work we initiate a study of correlation functions of energy flow operators on beauty and charm jets to illuminate the effects of the intrinsic mass of the elementary particles of QCD. We present a factorization theorem incorporating the mass of heavy quarks. Our results achieve a full next-to-leading-logarithmic calculation of a heavy quark jet substructure observable at the LHC.
We study the behavior of the correlators, and show that they exhibit a clear transition from a massless scaling regime, at precisely the scale of the heavy quark mass.This manifests the long-sought-after dead-cone effect and illustrates fundamental effects from the intrinsic mass of beauty and charm quarks in a perturbative regime, before they are confined inside hadrons.
The proposed Electron-Ion Collider (EIC) will utilize high-luminosity high-energy electron+proton ($e+p$) and electron+nucleus ($e+A$) collisions to solve several fundamental questions including searching for gluon saturation and studying the proton/nuclear structure. Due to their high masses ($M_{c,b} > \Lambda_{QCD}$), heavy quarks do not transfer into other quarks or gluons once they are produced. This feature makes the heavy flavor product an ideal probe to explore how a heavy flavor hadron is formed from a heavy flavor quark, which is referred to as the heavy quark hadronization. A series of heavy flavor hadron and jet simulation studies have been carried out with the newly developed EIC project detector conceptual designs. We will present reconstructed heavy flavor hadron mass and heavy flavor jet transverse momentum spectrums, the projected nuclear modifications of heavy flavor hadrons inside jets, and heavy flavor jet substructure distributions in $e+p$ and $e+A$ collisions with the EIC project detector design and the projected integrated luminosities at the EIC. These proposed EIC heavy flavor measurements will provide a unique path to constrain the accessed gluon parton distribution functions within the high Bjorken-x ($x_{BJ} > 0.1$) region, explore the flavor dependent fragmentation functions and reveal the heavy quark nuclear transport properties in cold nuclear meidum, which can constrain the initial and final state effects for previous and ongoing heavy ion measurements at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).
We present theoretical results for the associated production of a single top quark and a $Z$ boson ($tqZ$ production) at LHC energies. We calculate higher-order corrections from soft-gluon emission for this process. We compute the approximate NNLO (aNNLO) cross section at LHC energies, including uncertainties from scale dependence and from parton distributions. We also calculate the top-quark rapidity distribution. The aNNLO corrections are significant and enhance the NLO cross section, and their inclusion provides a more precise theoretical prediction.
In this talk, I will present NNLO QCD predictions for several differential distributions of B-hadrons in top-pair events at the LHC. In an extension of previous work, the decay of the produced B-hadron to a muon or a J/ψ meson has been incorporated, allowing us to make predictions for distributions involving those decay products as well. Additionally, a new set of B-hadron fragmentation functions has been obtained, which features reduced uncertainties and can be used consistently within the perturbative fragmentation function formalism employed in our calculation. Among other things, our predictions allow for a precise determination of the top-quark mass. The results also offer positive prospects for extracting heavy-flavour fragmentation functions from LHC data.
The identification of jets containing b-hadrons is key to many physics analyses at the LHC, including measurements involving Higgs bosons or top quarks, and searches for physics beyond the Standard Model. In this contribution, the most recent enhancements in the capability of ATLAS to separate b-jets from jets stemming from lighter quarks will be presented. The improved performance originates from the usage of state-of-the-art machine learning algorithms based on graph networks. A factor of more than 2 to reject light- and c-quark-initiated jet is observed compared to the current performance. The expected performance of this algorithm at the High-Luminosity LHC (HL-LHC) will also be discussed in detail.
An intuitive definition of the partonic flavor of a jet in quantum chromodynamics is often only well-defined in the deep ultraviolet, where the strong force becomes a free theory and a jet consists of a single parton. However, measurements are performed in the infrared, where a jet consists of numerous particles and requires an algorithmic procedure
to define their phase space boundaries. In this talk we introduce a novel and simple partonic jet flavor definition in the infrared. To connect these two regimes, we define the jet flavor to be the net flavor of the partons that lie exactly along the direction of the Winner-Take-All recombination scheme axis of the jet, which is safe to all orders under emissions of soft particles, but is not collinear safe. Collinear divergences can be absorbed into a perturbative fragmentation function that describes the evolution of the jet flavor from the ultraviolet to the infrared. The evolution equations are linear and a small modification to traditional DGLAP and we solve them to leading-logarithmic accuracy. The evolution equations exhibit fixed points in the deep infrared, we demonstrate quantitative agreement with parton shower simulations, and we present various infrared and collinear safe observables that are sensitive
to this flavor definition.
Investigating particle production in various collision systems has become in-
strumental in probing non-perturbative contributions to hadron structure and
hadronization. The LHCb spectrometer’s unique geometry among the LHC de-
tectors along with its particle identification and tracking capabilities allow for
new studies in hadron production to identify how said contributions manifest in
hadronic collisions. In this talk, we will discuss recent and upcoming measure-
ments from the LHCb collaboration regarding charged particle production and
hadronization as well as how they are modified based on collision system, loca-
tion in phase space, and event activity. We will also briefly describe the current
landscape of models which account for non-perturbative modifications in struc-
ture or hadronization and how these results help to identify which mechanisms
are contributing in hadron collisions; particularly small systems.
{Observables involving heavy quarks can be computed in perturbative QCD in two different approximation schemes: either the quark mass dependence is fully retained, or it is retained only where needed to regulate the collinear singularity. The two schemes have different advantages and drawbacks. In particular, it is known that the structure of large logarithms arising from soft emissions is different in the two approaches. We investigate the origin of this difference in some detail, focussing on a few specific processes. We show that it is related to the non-commutativity of the small-mass and soft-emission limits. Finally, we perform the resummation of soft-emission logarithms to next-to-leading accuracy in the case of Higgs decay into a $b\bar b$ pair, in the scheme in which the quark mass dependence is fully accounted for.
In this talk I will present a recent idea for which one could use the deadcone, a region suppressed by QCD in vacuum to massive kinematic effects, to measure properties of the Quark-Gluon-Plasma, due to in-medium enhancements for massive emitters.
Spin and 3D Structure
In operation since 2002, COMPASS is a fixed-target experiment located along the M2 beamline of the CERN SPS. One of the key measurements of its broad physics programme is the investigation of the transverse-momentum and transverse-spin structure of the nucleon, which has been pursued e.g. via measurements of Semi-Inclusive Deep Inelastic Scattering using a 160 GeV/$c$ muon beam and transversely polarized and unpolarized proton and deuteron targets.
Data have been collected with a transversely polarized deuteron target first in 2002-2004; together with those collected in 2007 and 2010 on a transversely polarized proton target, they allowed extracting unique and very important information on the transversity and Sivers distribution functions. The unbalance in the statistics collected on deuteron and on proton target, reflected in a large uncertainty on the transversity PDF for the $d$-quark compared to the $u$-quark, is one of the main reasons behind the 2022 data taking with a transversely polarized deuteron target. In this talk, along with a review of the major results obtained from the previous measurements on polarized and unpolarized targets, projections of the statistical uncertainties of the freshly collected 2022 data sample will be presented for the first time.
I will summarize recent progress in a reformulation of TMD factorization that guarantees a parsonic structure description of the small transverse momentum region while matching to standard fixed order collinear factorization at large transverse momentum. The focus will be on applications to semi-inclusive DIS.
We study the energy-energy correlator (EEC) for the process of unpolarized hadrons production from transversely polarized partons Semi-Inclusive Deep Inelastic Scattering (SIDIS) for the first time. In the factorization formula we present, this event shape observable is correlated with the Collins function in the back-to-back limit. We show the structure functions of all the possible spin asymmetries that can arise in these processes. In SIDIS, twist-2 transverse-momentum-dependent parton distribution functions (TMDPDFs) are convoluted with EEC jet functions in the structure functions, indicating a new direction for probing nucleon structures using EEC. With the analytical formalism derived, we defined the Collins EEC jet function and provide predictions for the Collins asymmetry correlated with transversely polarized EEC jet functions at EIC kinematics. As an example of probing nucleon structures using EEC jets, we also present a Sivers asymmetry prediction in terms of EEC jet functions for the future EIC.
In this analysis, we report a comparison of transverse momentum dependent parton distribution functions (TMDPDFs) between pions and protons through a simultaneous extraction of collinear and transverse degrees of freedom in the pion. We extract proton TMDPDFs along with pion TMDPDFs from low transverse-momentum dependent fixed-target Drell-Yan data as well as collinear pion PDFs from Drell-Yan and leading neutron data, marking the first analysis of its kind. We observe a very distinctive behavior of the conditional expectation value of the transverse separation of quarks for a given $x$. We provide some possible explanation of the phenomena and new avenues for further explorations.
The investigation of the hadrons spin-(in)dependent structure is one of the main goals of the COMPASS experiment at the M2 beamline of the CERN SPS. In particular, azimuthal transverse spin asymmetries provide a clean access to the transverse momentum dependent parton distribution functions (TMD PDFs) of the nucleon, still poorly known. In 2015 and 2018 COMPASS performed measurements of the Drell-Yan process from the interactions of a negative pion beam at 190 GeV impinging on a transversely polarized ammonia target and aluminium and tungsten targets. Such measurements allow to test the important QCD prediction of the (non-)universality of TMD PDFs, by confronting these with those previously obtained from semi-inclusive DIS reactions at COMPASS. The final results on the spin asymmetries in the Drell-Yan and J/psi production channels will be presented. The angular dependence of the Drell-Yan unpolarized cross section provides access to the pion and nucleon Boer-Mulders TMD functions. The recent COMPASS results will be shown. Finally, the kinematic dependences of the Drell-Yan cross section measured in ammonia and tungsten targets will be presented for the first time.
The structure of the proton has been studied by measuring the parton distribution function, which is the parton density distribution as a function of the longitudinal momentum of the parton, for long time. In the last few decades, the three-dimensional imaging of nucleon, such as the transverse momentum dependent parton distribution functions (TMDs), has received attention to better understand the structure of the nucleon. The Boer--Mulders function is one of the TMDs that represents the correlation between the transverse spin and the transverse momentum of the quark. The Boer--Mulders function can be extracted from the azimuthal angular distribution of the Drell--Yan process. In the naive Drell--Yan model, the angular distribution of the Drell--Yan process has a $\cos\theta$ modulation ($\lambda=1$) while no $\cos2\phi$ ($\nu=0$) modulation, where $\theta$ and $\phi$ denote the polar and azimuthal angle, respectively. However, the sizable $\cos2\phi$ modulation has been observed by NA10 and E615 experiments, which are pion-induced Drell--Yan experiments. The E866 experiment reported the first and only results of the angular distribution of the proton-induced Drell--Yan process using 800 GeV proton beam. In contrast to pion-induced Drell--Yan experiments, E866 shows significantly smaller $\cos2\phi$ modulation.
The SeaQuest experiment is a Drell--Yan experiment at Fermilab that measured the Drell--Yan dimuons using the 120 GeV proton beam colliding with liquid hydrogen and deuterium targets. We have measured the angular distribution of the proton-induced Drell--Yan dimuons in a kinematics region different of E866. In this talk, the progress of the angular distribution analysis will be presented.
One of the most important unresolved puzzles of the proton is the “proton spin puzzle”. Originally, the proton spin was assumed to be produced only by the valence quark spins, with no contribution from sea quarks or from gluons, and no contribution from orbital angular momentum. However, the contribution of the spins of both quarks and antiquarks to the proton spin have been measured over the past decades and is only about 30%. Many additional contributions have been considered to solve this puzzle. One of them is the contribution of the orbital angular momenta (OAM) of quarks and antiquarks.
The Sivers function, which represents the correlation between the transverse momentum of a quark and the spin of the parent hadron, can give some hints about the OAM contribution. The Sivers function of valence quarks has been measured by several experiments mainly using SIDIS. On the other hand, the Sivers function of antiquarks has not been determined precisely because SIDIS is not sensitive to them. The Drell-Yan process gives a window into the transverse momenta of the quark-antiquark pair, and thus a view of the antiquarks Sivers function. Another importance of the Sivers function measurement by the Drell--Yan process is that it can be utilized for investigating the sign change of the Sivers function by Drell--Yan and SIDIS.
The SpinQuest experiment will observe the transverse single spin asymmetry in the Drell-Yan production of muon pairs with the aim of extracting the Sivers functions of the light sea quarks in the proton, using polarized fixed-targets of NH$_3$ and ND$_3$ and the 120 GeV unpolarized proton beam from the Fermilab Main Injector. In this talk, the progress of the SpinQuest experiment will be presented.
Understanding the spin structure of the proton is of large interest to the nuclear physics community and it is one of the main goals of the spin physics program at the Relativistic Heavy Ion Collider (RHIC). Measurements from data taken by the PHENIX detector with transverse (p$^{\uparrow}$ + p, p$^{\uparrow}$ + Al, p$^{\uparrow}$ + Au) proton polarization play an important role in this, in particular, due to the leading order access to gluons in polarized protons. Transverse single-spin asymmetries (TSSAs) provide insight into initial and final state spin-momentum and spin-spin parton-hadron correlations. In addition to possible final state contributions, $\pi^{0}$ and $\eta$ TSSAs access both quark and gluon correlations in the polarized proton. Furthermore, the p$^{\uparrow}$ + A data from RHIC provides an opportunity to study the effect of TSSAs in the presence of additional nuclear matter. Midrapidity $\pi^{0}$ and $\eta$ mesons are measured at PHENIX by detecting the 2$\gamma$ decay with the electromagnetic calorimeter (EMCal) in the central arm spectrometer, which has fine granularity for the resolution of separate decay photons. New results for TSSAs of midrapidity $\pi^{0}$ and $\eta$ mesons in $\sqrt{s} = 200$ GeV p$^{\uparrow}$ + Au and p$^{\uparrow}$ + Al collisions from the 2015 running year will be presented and compared with the recent $\sqrt{s} = 200$ GeV p$^{\uparrow}$ + p results.
Future Experiments
Generalized parton distributions (GPDs) are off-forward matrix elements of quark and gluon operators that work as a window to the total angular momentum of partons, making it possible to solve the spin puzzle that emerged after EMC measurements. In addition, GPDs enable tomography of the nucleon allowing to study spatial distribution of partons as a function of momentum, providing clear imaging of the nucleon. To access GPDs one needs to look into exclusive processes, such as deeply virtual and timelike Compton scattering (DVCS and TCS), for both of which there is already experimental data. However, at LO these processes are mainly sensitive to GPDs in a restricted kinematic domain, namely $x =|\xi|$, where $x$ represents the average fraction of longitudinal momentum carried by an active parton, while $\xi$ is the so-called skewness parameter. To directly probe LO GPDs at $x \neq |\xi|$, it was proposed to study double deeply virtual Compton scattering (DDVCS), where an electron beam scatters off a nucleon and produces a lepton pair. Such sensitivity is possible thanks to the extra virtuality with respect to DVCS and TCS, which modifies the form of the coefficient functions in the hard part of the process. Existence of two independent virtualities results in the rich analytic structure of DDVCS amplitude, being the consequence of a mixed spacelike-timelike nature of the process.
In the last years, due to the features described above, there has been a growing interest in DDVCS. Because of that, in this talk, I present a new formulation of DDVCS based on the methods developed by R. Kleiss and W. J. Stirling in the 1980s. These techniques render expressions for amplitudes that are perfectly suited for phenomenology. Elements of impact studies, including predictions for experiments such as JLab12, JLab20+ and the Electron-Ion Collider (EIC), have been studied by means of PARTONS software and EpIC Monte Carlo event generator, and will be shown as well.
Since the EMC collaboration measurement of the small quark spin contribution to the proton spin in the late 1980s, the nuclear physics community has been actively working to resolve the so-called proton spin puzzle. While the size of the quark spin contribution is fairly well established, the gluon spin contribution is not as well established and recently has met theoretical tension. Recent global QCD analyses of jet production and other polarized scattering data find the presence of negative gluon helicity distributions, $\Delta g$, compatible with the existing data in addition to the traditional positive $\Delta g$ distributions. In this work, we present an analysis of semi-inclusive deep inelastic scattering for produced hadrons with large transverse momentum for further constraint of the dependence of $\Delta g$ on the parton momentum fraction, $x$, and focusing on the double longitudinal spin asymmetry, we identify kinematic regions relevant to future experiments at JLab and the Electron-Ion Collider which are particularly sensitive to $\Delta g$ and are capable of distinguishing the different $\Delta g$ distributions.
Solenoidal Large Intensity Detector (SoLID) is a large acceptance, high luminosity device proposed for exploiting the full potential of the Jefferson Lab 12 GeV energy upgrade. The scientific program of SoLID includes three semi-inclusive deep inelastic scattering (SIDIS) experiments with multiple run-group experiments. One of the major tasks of SoLID is to deepen our knowledge of the nucleon structure, which,
in terms of its partons constituents, can be described by a five-dimensional quantum phase space distribution called Wigner distribution. Integrating the Wigner distribution over its intrinsic transverse coordinates leads to the transverse-momentum-dependent (TMD) parton distribution function. The TMD is experimentally accessible via the SIDIS process. It depicts a three-dimensional momentum imaging of the nucleon and plays an essential role in understanding its spin structure. In this talk, an overview of the SoLID-SIDIS program and projections of the 3D imaging of the nucleon will be presented.
In this talk, we will provide an overview of future parity violation deep inelastic scattering (PVDIS) experiments by using the Solenoidal Large Intensity Device (SoLID) at Jefferson Lab (JLab) Hall A. We will obtain data with high statistic and large kinematic coverage for Bjorken $0.25
A precision measurement of inclusive neutron spin structure function $g_{2} (x,Q^{2})$, will be run in parallel with SIDIS experiments E12-010-006 (transversely polarized $^{3}$He target) and E12-11-007 (longitudinally polarized $^{3}$He target) by using a Solenoidal Large Intensity Device (SoLID) at Jefferson Lab (JLab) Hall A, as has been approved by JLab PAC48 in 2020. In the proposed experiment, high statistics data will be collected within a large kinematic coverage of Bjorken scaling $x > 0.1$ and four momentum transfer $ 1.5
The Large Hadron-electron Collider and the Future Circular Collider in electron-hadron mode [1] will make possible the study of DIS in the TeV regime providing electron-proton collisions with per nucleon instantaneous luminosities around $10^{34}$ cm$^{-2}$s$^{-1}$. In this talk we will review the opportunities for measuring standard and anomalous top couplings, both to lighter quarks and to gauge bosons through $t \bar t$ production. We will discuss the studies in inclusive DIS of different EW parameters like the effective mixing angle and the gauge boson masses, and weak neutral and charged current couplings of the gauge bosons. We will also review the possibilities in direct $W$ and $Z$ production, and analyse the implications of a precise determination of parton densities at the LHeC or FCC-he on EW measurements at hadronic colliders.
[1] LHeC Collaboration and FCC-he Study Group: P. Agostini et al., J. Phys. G 48 (2021) 11, 110501, e-Print: 2007.14491 [hep-ex].
The dependence of the top-quark mass measurement in top-quark production on the parton distribution functions (PDF) is explored through differential mass distributions in $t\bar{t}$ and $t\bar{t}j$ production at the LHC and a future 100 TeV proton-proton collider. The top-quark mass uncertainty is obtained from chi-squared fits to invariant mass distributions from simulations assuming different top pole masses around the nominal value of 172.5 GeV. The PDF uncertainties of the differential distributions are used in the chi-square evaluation and reduced through a fit to differential distributions in $t\bar{t}$ and $t\bar{t}j$ production. I will present the resulting reduced top pole mass uncertainties.
We review the status of the Large Hadron-electron Collider and the Future Circular Collider in electron-hadron mode after the publication of the update of the 2012 Conceptual Design Report in [1] and the studies on a joint $eh-hh$ interaction region and experiment in [2]. We also comment on the main technical challenges of these proposals and describe further steps of work towards the Update of the European Strategy for Particle Physics expected by about 2026.
[1] LHeC Collaboration and FCC-he Study Group: P. Agostini et al., J. Phys. G 48 (2021) 11, 110501, e-Print: 2007.14491 [hep-ex].
[2] K.D. J. Andre et al., Eur. Phys. J. C 82 (2022) 1, 40, e-Print: 2201.02436 [hep-ex].
The Large Hadron-electron Collider and the Future Circular Collider in electron-hadron mode [1] will make possible the study of DIS in the TeV regime providing electron-proton collisions with per nucleon instantaneous luminosities around $10^{34}$ cm$^{-2}$s$^{-1}$. We review the possibilities for detection of physics beyond the SM in these machines, focusing on feebly interacting particles like heavy neutrinos or dark photons, on anomalous gauge couplings, and on theories with heavy resonances like leptoquarks, or with contact interactions.
[1] LHeC Collaboration and FCC-he Study Group: P. Agostini et al., J. Phys. G 48 (2021) 11, 110501, e-Print: 2007.14491 [hep-ex].
A renewed attention has spawned in recent years to the pion parton distribution functions (PDFs). In 2018, the JAM collaboration included not only the pion-induced Drell-Yan data from Fermilab’s E615 experiment but additionally the leading neutron electroproduction data from HERA for the first time in a global QCD analysis. Unfortunately, further useful experimental data have been scarce. With the upcoming tagged deep inelastic scattering (TDIS) experiment at JLab, which is a fixed-target complement to the leading neutron experiment, and the electron ion collider (EIC), we have an opportunity to further study pion structure. I will discuss to what extent the pion PDFs can be constrained with these experiments, with a special focus on the resonance region of the pion.
The structure of hadrons relevant for deep-inelastic scattering are completely characterised by the Compton amplitude. A direct calculation of the Compton amplitude provides a complementary way to accessing the structure functions, circumventing the operator mixing and renormalisation issues of the standard operator product expansion approach.
In this talk, we focus on the QCDSF/UKQCD Collaboration's advances in calculating the forward Compton amplitude via an implementation of the second-order Feynman-Hellmann theorem. We highlight our progress in investigating the moments of nucleon structure functions.
Studying the structure of Nucleons in Quantum Chromodynamics is a challenging task due to the appearance of non-perturbative Parton Distribution Functions (PDF).
PDFs describe the distributions of quarks and gluons with respect to the longitudinal momentum and appear in cross-sections as process-independent contributions.
Lattice QCD provides the possibility to study these by calculating their Mellin moments.
We present a calculation of the Axial, Vector and Tensor moments and discuss the corresponding analysis.
We present the first physical-continuum limit $x$-dependent nucleon gluon distribution from lattice QCD using the pseudo-PDF approach, on lattice ensembles with $2+1+1$ flavors of highly improved staggered quarks (HISQ), generated by MILC Collaboration. We use clover fermions for the valence action on three lattice spacings $a \approx 0.9$, 0.12 and 0.15~fm and three pion masses $M_\pi \approx 220$, 310 and 690~MeV, with nucleon two-point measurements numbering up to $O(10^6)$ and nucleon boost momenta up to 3~GeV. We study the lattice-spacing and pion-mass dependence of the reduced pseudo-ITD matrix elements obtained from the lattice calculation, then extrapolate them to the continuum-physical limit before extracting $xg(x)/\langle x \rangle_g$.We use the gluon momentum fraction $\langle x \rangle_g$ calculated from the same ensembles to determine the nucleon gluon unpolarized PDF $xg(x)$ for the first time entirely through lattice-QCD simulation. We compare our results with previous single-ensemble lattice calculations, as well as selected global fits.
Parton distribution functions (PDFs) are defined from matrix elements of operators separated along the light cone, which cannot be determined directly from calculations performed in Euclidean space. Despite this, various approaches for extracting information on PDFs from lattice QCD have been developed, all of which involve a factorization of the lattice QCD computed matrix element with perturbatively calculable matching coefficients. We will present recent work on the extraction of the valence pion PDF in the continuum and the unpolarized isovector quark PDF of the nucleon using two main strategies. While the first one is based on factorization in position space, the second one relies on factorization in momentum space. We extract the $x$-dependent PDFs using both methods and compare these results with those obtained from the phenomenological global fits. We then present independent calculations of the moments of the PDFs based on the operator product expansion of the lattice QCD computed matrix elements in position space and show comparisons with the corresponding phenomenological global fit results. All lattice QCD calculations were carried out with the physical value of the pion mass, and all analyses used perturbative matching coefficients computed at next-to-next-to-leading order (NNLO) in the strong coupling.
We present a lattice QCD calculation of the unpolarized isovector quark parton distribution function (PDF) of the proton utilizing a perturbative matching at next-to-next-leading-order (NNLO). The calculations are carried out using a single ensemble of gauge configurations generated with $N_f$ = 2+1 highly improved staggered quarks with physical masses and a lattice spacing of a =0.076 fm. We use one iteration of hypercubic smearing on these gauge configurations, and the resulting smeared configurations are then used for all aspects of the subsequent calculation. For the valence quarks, we use the Wilson-clover action with physical quark masses. We consider several methods for extracting information on the PDF. We first extract the lowest four Mellin moments using the leading-twist operator product expansion approximation. Then, we determine the x dependence of the PDF through a deep neural network within the pseudo-PDF approach and additionally through the framework of large-momentum effective theory utilizing a hybrid renormalization scheme. This is the first application of the NNLO matching coefficients for the nucleon directly at the physical point.
The fact that lattice QCD is defined in a finite-Euclidean spacetime, prohibits direct access of inclusive scattering observables from lattice QCD. In principle, one can envision determining such quantities from real-time computations, such as those that may be eventually performed using quantum computers. Looking forward into the future, in this talk I outline a possible pathway towards determining inclusive scattering observable from real time matrix elements. I enumerate some new challenges encountered in this framework, as well as possible solutions.
Factorization theorems have long been a successful and elegant tool to describe and interpret hadronic structure. The early parton model picture, first developed by Feynman, has now been generalized past the leading power description of inclusive processes like deep inelastic scattering (DIS) to semi-inclusive ones like SIDIS and much more. However, a consistent description of both collinear and TMD distribution functions is still not agreed upon along with the limits of the factorization program. The inherent complexity of QCD prohibits a direct test of factorization but any other simpler renormalizable theory can be adopted to stress-test its validity and the schemes regularly used to describe physical observables like cross sections and structure functions.
A scalar Yukawa model, free of gauge degrees of freedom, can be studied as toy-model to quantitatively tackle issues such as the positivity of collinear PDFs (and FFs) and their possible definitions as the integrated versions of TMD distributions. The performance of the well known $b_*$ prescription can also be compared directly along with quantitative results on the role of the W and Y term in the description of TMD observables.
The information obtained by studying a simpler model that still retains some of the features of QCD could shed light onto many of the standard schemes employed in regular QCD and cast some doubts on the various assumptions that are made.
The splitting functions determine the scaling violations of deep-inelastic scattering structure functions and govern the evolution of Parton densities. A determination of N3LO Parton densities requires the knowledge of 4-loop splitting functions. It is important to find efficient methods to compute 4-loop splitting functions. The method of computing the off-shell matrix elements with a twist-two operator insertion is one of the most efficient methods. However, the nature of off-shell quantity in the unpolarized case requires us to find all gauge-variant operators which mix with the physical twist-two operators.
In this talk, I will introduce a systematic framework to determine all gauge-variant operators, and apply the framework to determine the unpolarized singlet splitting functions to the three-loop order. Our framework can also be directly applied to determine all counterterms to extract the 4-loop splitting functions.
In this talk we discuss on recent result on massless and massive Wilson
coefficients in the polarized and unpolarized case up to 3-loop order.
This includes the gluonic massive operator matrix element $A_{gg}$
which enters the definition of the Variable-Falvor-Number-Scheme, and the
calculation of the unpolarized and polarized massless Wilson coefficients.
While the calculation of the unpolarized case is the first independent calculation
of these quantities, the result for $g_1$ is obtained for the first time and
is a necessary ingredient to obtain the polarized massive Wilson coefficients in
the asymptotic limit.
We have calculated the $n_f^2$ and $n_f^3$ contributions to the flavour non-singlet structure functions $F_2$ and $F_L$ in inclusive deep-inelastic scattering at the fourth order in the strong coupling $\alpha_s$. The coefficient functions have been obtained by computing a very large number of Mellin-N moments using the method of differential equations, and then determining the analytic forms in N and Bjorken-x from these. Our new $n_f^2$ terms are numerically much larger than the $n_f^3$ leading large-nf parts which were already known; they agree with predictions of the threshold and high-energy resummations. Furthermore our calculation confirms the earlier determination of the four-loop $n_f^2$ part of the corresponding anomalous dimension. The next step is to obtain the expression for the $F_3$ structure function and therefore complete the unpolarized contributions for $n_f^2$ and $n_f^3$ at four-loop.
The factorization theorem plays an important role in the analysis of high energy quantum chromodynamic (QCD) processes, separating the nonperturbative hadronic interaction into the universal parton distribution functions (PDFs) and fragmentation functions (FFs) and the process-dependent interactions into short distance perturbative calculations, with any interference power suppressed. With a virtual photon exchange, lepton-hadron deep inelastic scattering (DIS) provides an electromagnetic hard probe for the partonic structure of colliding hadron and has played an important role in the development of QCD factorization. However, the collision induced QED radiation can change the momentum of the exchanged but unobserved virtual photon, making the photon-hadron frame, where the factorization formalism for DIS and semi-inclusive DIS (SIDIS) was derived, ill defined. An new analogous factorization approach has been introduced to separate the leading power process-independent QED radiative contributions to the single photon exchange by introducing lepton distribution functions (LDFs) and lepton fragmentation functions (LFFs), while process-dependent effects are perturbatively calculated with large logarithms removed [J. High Energ. Phys. 2021, 157 (2021)]. These LDFs and LFFs are considered global, as they appear in many different interactions, such as $e^+ e^-$, DIS and SIDIS, so data from experiments can be used to fit and describe these functions across a wide range of lepton scattering. In this talk, I will apply this new factorization approach to lepton-hadron SIDIS to study the cross-section in two different kinematic regions: (1) the scattered lepton and observed hadron are not near back-to-back, and (2) they close to back-to-back, where collinear QCD factorization works for (1) and TMD QCD factorization for (2) while collinear QED factorization for both, in a newly introduced hybrid factorization approach. As part of this work, I derived the NLO perturbative coefficients for SIDIS in both regions, and investigate the matching between these two regions.
Small-x, Diffraction and Vector Mesons
The Good-Walker paradigm is widely used for studying ultra-peripheral collisions (UPCs) and underlies much of the exclusive photoproduction/electroproduction program at the future electron-ion collider (EIC). It relates the cross-section for coherent photoproduction, $d\sigma/dt$ to the transverse distribution of scattering centers in a target, and ties the incoherent cross-section to fluctuations of the target configuration, including gluonic hotspots. In this talk, I will present examples where the Good-Walker approach clearly fails, and compare the predictions with a semi-classical approach. I will explain why it fails, and show that the problem is general, including both UPCs and an EIC. I will discuss some possible expansions that will allow it to work in UPCs and at an EIC.
Photon-induced reactions in ultra-peripheral collisions (UPCs) of heavy nuclei at the LHC have been studied using the ALICE detector for several years. The ALICE detector can measure the photoproduction cross section for vector mesons at various rapidities, centre-of-mass energies and
collision systems. Beyond the recent ALICE studies of the rapidity and momentum transfer dependence of coherent J/$\psi$ photoproduction, new results on coherent J/$\psi$ measurements with forward neutron tagging will be presented for the first time. In addition, new results on the momentum transfer dependence of incoherent J/$\psi$ photoproduction will also be discussed for the first time. These new results complement coherent J/$\psi$ measurements and provide additional sensitivity to probing nuclear gluon effects including the presence of subnucleon gluon fluctuations. Additionally, new measurements of the coherent and incoherent J/$\psi$ polarization will be shown. These new results serve testing the s-channel helicity conservation hypothesis.
High energy photons originating from the electromagnetic field of ultrarelativistic lead nuclei can interact with the other lead beam. These reactions are studied in the ultra-peripheral heavy ion collisions to probe the physics of strong interactions. The analysis of dipion and dikaon photoproduction was carried out using the ALICE 2015 Pb-Pb data at center-of-mass energy $\sqrt{s_{NN}}=5.02$ TeV. We will be presenting the $\rho^0$ meson and direct $\pi^+\pi^-$ measurements, as well as the prospects of studying exclusive $K^+K^-$ photoproduction, with sensitivity towards higher dikaon invariant mass above the $\phi(1020)$ threshold.
Baryon number is a strictly conserved quantity in QCD. Conventionally it is assumed to be split between the three valence quarks, but the baryon junction has also been proposed as a way of constructing a gauge-invariant baryon wave function. The baryon junction is a nonperturbative Y-shaped configuration of gluons that is connected to all three valence quarks and carries the baryon number. Baryon number is closely associated with baryon stopping: an excess of baryons compared to antibaryons at midrapidity which is caused by the target nucleons being veered away from the beamline. By definition the junction carries a much lower momentum fraction compared to the valence quarks, and so it has more time to interact with and be stopped by the projectile. In this model the baryon electric charge is still carried by the valence quarks so we can look for evidence of the baryon junction by comparing charge stopping to baryon stopping. This is done with the STAR isobar data set of ${}^{96}_{44}\rm{Ru} + {}^{96}_{44}\rm{Ru}$ and ${}^{96}_{40}\rm{Zr} + {}^{96}_{40}\rm{Zr}$ collisions at $\sqrt{s_{NN}} = 200~\rm{GeV}$ by comparing how the midrapidity net-baryon and net-charge yields change between the two collision species based on the identified particle spectra. Photonuclear collisions occur in heavy-ion collisions when one nucleus emits a quasi-real photon which interacts with the other colliding nucleus, similar to an $e+A$ collision except that the photon tends to have a much lower virtuality. Further supporting the argument for the existence of the baryon junction, significant baryon stopping and rapidity asymmetry are observed at low transverse momentum in semi-inclusive photonuclear processes in $\rm{Au}\rm{+}\rm{Au}$ collisions at $\sqrt{s_{NN}} = 54.4~\rm{GeV}$. These measurements will inform future measurements of identified particles at RHIC and the LHC, as well as measurements in $e+p/A$ collisions at the EIC.
Exclusive coherent and incoherent \jpsi photoproduction in Au$+$Au ultra-peripheral collisions (UPC) are measured at
$\sqrt{s_{_\mathrm{NN}}}=200$ GeV using the STAR detector.
Measurements of the differential cross sections as functions of rapidity $y$ and \ptSquare $\approx -t$ of the $J/\psi$ are reported.
Results for different combinations of neutron emission, detected in zero degree calorimeters, are also presented.
The different neutron emissions enable the resolution of the photon energy ambiguity inherent in UPCs,
allowing measurement of the coherent cross section of $\gamma + {\rm Au} \rightarrow J/\psi + {\rm Au}$ as a function of the photon-nucleon center-of-mass energy $W_{\rm{\gamma N}}$.
For the first time at the top RHIC energy, the momentum transfer $-t$ of \jpsi photoproduction is measured up to $2.25~\rm{(GeV/c)^2}$,
where the large $-t$ region is dominated by incoherent production.
The incoherent \jpsi photoproduction measurements strongly suggest the presence of sub-nucleonic shape fluctuations in heavy nuclei,
which is a major step forward towards understanding the initial-state dynamics of heavy-ion collisions.
Both the coherent and incoherent \jpsi cross sections are found to be strongly suppressed relative to those of
$\gamma + p \rightarrow J/\psi +p$.
Within the kinematic range $x_{\rm{parton}}\sim0.015-0.03$,
the reported data provide important experimental constraints for nuclear parton distribution functions.
The outlook for significantly improved measurements during the final RHIC runs in 2023-2025 is discussed.
These measurements also demonstrate the potential opportunities and challenges of performing gluon tomography measurements
via coherent vector meson production at the upcoming Electron-Ion Collider.
In this contribution I would like to present our recent computation of exclusive eta_c production in e+p and e+A collisions [1] in the Color Glass Condensate framework. While the original suggestion for this channel as a potential probe of the QCD odderon [2] was made some time ago [3], obtaining a realistic estimate for the cross section remains a challenge. A recent attempt at moderate-x was made here [4]. Our main goal is to try and improve this situation, thereby assesing the potential for the measurement of exclusive eta_c at the EIC. Focusing on small-x kinematics we have explicitly solved the running coupling Balitsky-Kovchegov (BK) equation for the coupled pomeron-odderon distributions in case of a proton and a nuclear target. For the pomeron we have used the initial condition set by the phenomenological fit [5] that, together with the unitarity of the dipole distribution, provides some constraints on the odderon. Since the odderon distribution is explicitly impact parameter $b_T$ dependent, we have solved the BK system by treating $b_T$ as an external parameter. Using this setup we are able to get an upper bound of the eta_c cross section in this particular model. In a comprehensive study for the EIC kinemtics, our cross section estimates also take into account the background in case when the target emits a coherent photon.
[1] SB, Horvatic, Kaushik, Vivoda, in preparation
[2] Lukaszuk, Nicolescu, Lett. Nuovo Cim. 8, 405 (1973)
[3] Czyzewski, Kwiecinski, Motyka, Sadzikowski, Phys. Lett. B 398 (1997)
[4] Dumitru, Stebel, Phys. Rev. D 99, 094038 (2019)
[5] Lappi, Mantysaari, Phys. Rev. D 88, 114020 (2013)
We provide the first calculation of two-gluon production at mid-rapidity in ultra-peripheral collisions in the Color Glass Condensate framework. To estimate systematic uncertainty associated with poor understanding of the wave function of the nearly real photon, we consider two diametrically different models: the dilute quark-antiquark dipole approximation and a
vector meson, in which color charge density is approximated by McLerran-Venugopalan model. In the experimentally relevant range, the target nucleus can be faithfully approximated by a highly saturated state. This simplification enables us to perform efficient numerical simulations and extract the two-gluon correlation functions and the associated azimuthal harmonics.
Photonuclear interactions are studied in ultra-peripheral p-Pb collisions with the ALICE experiment, where the photon radiated by a Pb nucleus probes the gluon density of the proton at low Bjorken-x. The exclusive J/𝜓 photoproduction cross section 𝜎(𝛾+𝑝→𝐽/𝜓+𝑝) is expected to follow a power law trend as x decreases, but it should deviate from this trend at low x due to gluon saturation. In addition, gluon saturation effects are also expected to be visible when studying the dissociative 𝐽/𝜓 photoproduction cross section 𝜎(𝛾+𝑝→𝐽/𝜓+𝑋) because of reduced quantum fluctuations of the substructure of the proton in the saturation regime. The ALICE collaboration has measured both processes. In this talk, the first measurement of the dissociative J/𝜓 photoproduction at the LHC will be presented. Finally, we will present the study of dimuon events produced in two-photon interactions. First results for low-mass dimuons will be discussed. Such measurements complement the studies of J/𝜓 photoproduction and contribute to a better understanding of the photon fluxes generated by the lead nucleus.
We describe the status of the ATLAS Forward Proton Detectors (AFP) in Run 2 and the outlook for Run 3 analyses.
The performance as well as Run 3 improvements of detector subsystems are discussed in detail. This includes the Tracking and Time-of-Flight Detectors, the electronics, the trigger, the readout, detector control and data quality monitoring.
Additionally, key physics results from the first AFP analyses are showcased.
The purpose of the ALFA detector is to measure protons scattered at very small angles. ALFA aims to study elastic and diffractive events, exclusive production and photon-induced interactions. In LHC Run 2, ALFA participated in the ATLAS high-luminosity data taking, as well as, special runs with reduced luminosity and dedicated optics.
This report presents the status of the ALFA detector during the LHC Run 2, including the tracker and the trigger performance, as well as, some details concerning the electronics and the readout system.
Additionally, key physics results from the ALFA analyses are showcased and possible future interests are discussed.
Electroweak Physics and Beyond the Standard Model
The presence of a non-baryonic Dark Matter (DM) component in the Universe is inferred from the observation of its gravitational interaction. If Dark Matter interacts weakly with the Standard Model (SM) it could be produced at the LHC. The ATLAS Collaboration has developed a broad search program for DM candidates in final states with large missing transverse momentum produced in association with other SM particles (light and heavy quarks, photons, Z and H bosons, as well as additional heavy scalar particles) and searches where the Higgs boson provides a portal to Dark Matter, leading to invisible Higgs decays. The results of recent searches on 13 TeV pp data from the LHC, their interplay and interpretation will be presented.
Supersymmetry (SUSY) provides elegant solutions to several problems in the Standard Model, and searches for SUSY particles are an important component of the LHC physics program. This talk will present the latest results from SUSY searches conducted by the ATLAS experiment. The searches target multiple final states and different assumptions about the decay mode of the produced SUSY particles, including searches for both R-parity conserving models and R-parity violating models and their possible connections with the recent observation of the favour and muon g-2 anomalies. The talk will also highlight the employment of novel analysis techniques, including advanced machine learning techniques and special object reconstruction, that are necessary for many of these analyses to extend the sensitivity reach to challenging regions of the phase space.
A new search for supersymmetry targeting pair production of squarks or gluinos decaying to sleptons or W, Z with final stated with either two leptons (electrons or muons) with the same electric charge or at least three leptons is presented. The analysis uses 139 fb-1 of pp collision data at 13 TeV collected with the ATLAS detector during Run 2 of the Large Hadron Collider, and simplified models with and without R-parity conservation are considered. The data-driven and Monte Carlo based methods used to estimate the Standard Model and detector backgrounds are discussed. Finally, the results in the defined signal regions, and the exclusion limits, are presented illustrating the significant improvement over the previous exclusion limits.
The Precision Proton Spectrometer (PPS) is a new subdetector of CMS introduced for the LHC Run 2 and will continue to operate during LHC Run 3. PPS provides a powerful tool for the advancement of BSM searches. The talk will present recent results obtained with the PPS subdetector illustrating the unique sensitivity achieved using proton tagging.
Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents a series of measurements of dilepton production from photon fusion performed by the ATLAS Collaboration. Recent measurements of exclusive dielectron production in ultra-peripheral collisions (UPC) are presented. These processes provide strong constraints on the nuclear photon flux and its dependence on the impact parameter and photon energy. Comparisons of the measured cross-sections to QED predictions from the Starlight and SuperChic models are also presented. Measurements of muon pairs produced via two-photon scattering processes in hadronic (i.e. Non-UPC) Pb+Pb collisions are also presented. These non-UPC measurements provide a novel test of strong-field QED and may be a potentially sensitive electromagnetic probe of the quark-gluon plasma. These measurements include the dependence of the cross-section and angular correlation on the mean-pT of the dimuon pair, the rapidity separation between the muons, and the pair angle relative to the second-order event-plane, all measured differentially as a function of the Pb+Pb collision centrality. The presented results are compared with recent theory calculations.
Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes. This talk presents searches for physics beyond the standard model enabled by photon-photon processes in both di-tau and di-photon final states. The tau-pair production measurements can constrain the tau lepton's anomalous magnetic dipole moment (g-2), and a recent ATLAS measurement using muonic decays of tau leptons in association with electrons and tracks provides one of the most stringent limits available to date. Similarly, light-by-light scattering proceeds via loop diagrams, which can contain particles not yet directly observed. Thus, high statistics measurements of light-by-light scattering shown in this talk provide a precise and unique opportunity to investigate extensions of the Standard Model, such as the presence of axion-like particles.
QCD with Heavy Flavours and Hadronic Final States
Charmonium is one of the most prominent probes used to investigate and quantify the properties of the quark-gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions. Thanks to its larger size and weaker binding energy, the excited $\psi$(2S) state is expected to be affected differently by the nuclear medium with respect to the J/$\psi$ state, therefore the effects of nuclear medium on its production might be significantly different. The regeneration mechanism, within the QGP or at the phase boundary, is an important ingredient for describing the J/$\psi$ production at LHC energies. $\psi$(2S) production relative to J/$\psi$ represents one possible discriminator between regeneration scenarios. Moreover, the determination of the non-prompt J/$\psi$ production, originating from b-hadron decays, allows one to access the energy loss of b-quarks within the QGP, while prompt J/$\psi$ measurements permit a direct comparison with models implementing regeneration. Furthermore, heavy ions accelerated at ultra-relativistic energies generate a strong electromagnetic field, leading to photonuclear interactions during the collision. The photoproduction of the J/$\psi$ vector meson has been widely studied in ultra-peripheral collisions, where hadroproduction is negligible. In the last few years, this study was extended to heavy-ion collisions with nuclear overlap. The coherently photoproduced J/$\psi$ are sensitive to nuclear gluon distributions at low Bjorken-$x$, and might be used in future to probe the formed and fast-expanding QGP.
In this contribution, latest ALICE results on inclusive, prompt and non-prompt J/$\psi$ at midrapidity, on J/$\psi$ and $\psi$(2S) production at forward rapidity, and on coherent J/$\psi$ photoproduction in both rapidity regions will be shown in Pb--Pb collisions with nuclear overlap at $\sqrt s_{NN}$ = 5.02 TeV. The comparison with the available model calculations will be presented as well.
The production of quarkonium, a bound state of a heavy quark (charm or bottom) and its corresponding antiquark, can be decomposed in a hard-scale perturbative production of the quark-antiquark pair, and its subsequent hadronization into the bound state which can only be described by non-perturbative models, such as NRQCD. In hadronic collisions, the underlying event activity, usually quantified in terms of charged-particle multiplicity density, is mainly determined by soft particle production processes. By correlating measurements of quarkonium production and event activity in small systems, we can learn more about the interplay between hard and soft processes. In particular, such measurements are crucial to better understand how both scales are differently affected by mechanisms such as gluon saturation or Multiple Partonic Interactions. They allow one to investigate as well the possible formation of a deconfined medium in high-multiplicity pp collisions.
In this presentation, we will discuss the latest measurements carried out by the ALICE collaboration in pp collisions, at several center-of-mass energies and rapidity ranges, of quarkonium production as a function of charged-particle multiplicity. Both quantities were normalised to their corresponding average value. Results will be compared with available theoretical models.