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Topics to be discussed include latest theoretical and experimental results on Soft and Hard QCD at the LHC on:
Local organising committee: Jean-Philippe Lansberg (IJCLab Orsay, Chair), Huasheng Shao (LPTHE Paris, co-chair), Samuel Wallon (IJCLab Orsay, co-chair), Ajjath Abdul Hameed (LPTHE Paris & IJCLab Orsay), Ekta Chaubey (INFN Torino & LPTHE Paris), Chris Flett (Jyvaskyla U. and Helsinki Inst. of Phys.), Kate Lynch (UC Dublin & IJCLab Orsay), Laure Massacrier (IJCLab Orsay), Saad Nabeebaccus (IJCLab Orsay), Yelyzaveta Yedelkina (IJCLab Orsay & UC Dublin)
International Advisory Committee: S. Alekhin (IHEP PROTVINO), J. Blümlein (DESY), C. Duhr (Bonn), R. K. Ellis (IPPP Durham), T. Gehrmann (Univ. Zürich), E.W. N. Glover (IPPP Durham), J. Huston (MSU), J. Katzy (DESY), F. Maltoni (UCLouvain & Bologna), M. Mangano (CERN), Z. Nagy (DESY), E. Rizvi (Queen Mary), F. Siegert (Dresden), D. Stöckinger (Dresden), Z. Trócsányi (Budapest), Doreen Wackeroth (Buffalo), Ciaran Williams (Buffalo).
Previous editions:
A precise measurement of the mass of the W boson mass represents an important milestone of the LHC physics program to test the overall consistency of the Standard Model. In 2018 ATLAS experiment published a Mass measurement with 19MeV total uncertainty. Recently LHCb experiment published a new measurement compatible with the ATLAS measurement with 32 MeV total uncertainty. Both measurement are limited by physics modelling uncertainty.
The challenges related to the modelling of W-boson production and decay at LHC will be discussed.
The ultimate goal of LHC experiments is to reach 10MeV uncertainty on the W boson mass measurement. Ancillary measurements of Drell-Yan processes - which are fundamental input to reach this goal and reduce the physics-modelling uncertainties - will be presented.
The LHC results together with the recent Tevatron mW measurement will be also described in the context of the LHC Tevatron combination.
Finally very recent LHC experiment highlights will be also presented.
In my talk I am going to present recent result from ATLAS and CMS on top quark physics and electroweak single- and multi-boson production, with emphasis on vector-boson scattering.
I will review a selection of recent results in the context of EW and top-quark physics and I will discuss possible future developments.
Measurements of multijet production in ATLAS and CMS
I present theoretical predictions for the production of a W-boson in association with a bottomquark pair at hadron colliders at next-to-next-to-leading order (NNLO) in QCD, including the leptonic decay of the W-boson, while treating the bottom quark as massless. This calculation constitutes the very first $2 \to 3$ process with a massive external particle to be studied at such a perturbative order. Numerical results for the cross section and differential distributions are presented for the Large Hadron Collider. The definition of IRC-safe flavoured jets becomes subtle beyond NLO QCD. I discuss the application of a proposed flavour safe anti-kT algorithm to this process and discuss the phenomenology.
Measurements of jet substructure observables in ATLAS and CMS experiments
Using the CGC effective theory together with the hybrid factorization, 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).
We present new high precision predictions for bottom-quark pair production in hadronic collisions. These results are obtained through the implementation of a Monte Carlo event generator in the Powheg-Box framework, where the MiNNLOps method has been applied to match the next-to-next-to-leading order (NNLO) calculation to parton showers. Distributions inclusive over QCD radiation are NNLO accurate, while distributions for bottom-quark pair production in association with one final-state hard jet are next-to-leading order accurate. We validate our results against a fixed-order NNLO calculation and present a first comparison of NNLO+PS predictions with experimental data from the LHC.
Tuning of generators by the LHC experiments is presented.
In the colour decomposition approach to treating the SU(3) colour gauge group in automated event generators, the size of the colour matrix grows factorially with the number of external particles in the process. As such, the treatment of the colour degrees of freedom becomes the bottleneck for high-multiplicity QCD processes. We propose to utilize the large-$N_C$ expansion to obtain a sparse colour matrix at next-to-leading-colour accuracy which reduces the computation complexity from a factorial to a polynomial scaling at the parton-level. We examine this efficiency for both the fundamental and the colour-flow decompositions for processes with up to two quark pairs. This work is the first step towards an efficient and accurate event generator for processes with high number of QCD partons.
Two years ago, we introduced a new method for calculating Feynman diagrams more efficiently and transparently, the chirality-flow formalism. In this framework, which builds on the spinor-helicity formalism and is inspired by QCD colour flow, analytic tree-level Standard Model Feynman diagrams can be written down almost immediately as complex numbers, without the need for intermediate algebra. In this talk, I will introduce chirality flow, and --- as a proof-of-concept --- discuss how using it for massless QED makes MadGraph5_aMC@NLO a factor 2-10 times faster for processes with up to 7 final-state particles, with increasing speed gain for increasing multiplicity.
Photoproduced dijets are a useful probe of gluon distributions inside nuclei. Recent ATLAS results from 2018 data are presented, showing the current progress in mapping these one-dimensional parton distributions with differential cross sections. To move forward in understanding higher order gluon distributions, the angular correlations of these gluons must be measured. CMS results from 2015 measuring such photoproduced dijet angular correlations are presented. Similar CMS studies on 2018 data will be done to improve upon these measurements.
We discuss the impact of soft gluon emissions on the azimuthal angular correlation between two jets produced in high energy collisions. We find a good description on the recent CMS data on dijet production in UPC events.
We present the MCscales approach for incorporating scale uncertainties in parton
distribution functions. The method builds on the Monte Carlo sampling method
for propagating experimental uncertainties to PDFs that underlies the NNPDF
approach, by extending it to the space of factorisation and renomalisation
scales for the processes entering a PDF fit . Our approach allows one to exactly match the scale variations in the PDFs with those in the partonic cross section, thus
accounting for the full correlations between the two. We illustrate the
opportunities for phenomenological exploration made possible by our
methodology, by studying the correlations between scale variations in PDFs
and those in the partonic cross sections for a variety of LHC observables. Sets of PDFs enriched with scale information are provided, along with a set of tools to use them.
The transverse momentum dependent and collinear factorization theorems are independent approaches to the description of scattering cross-sections at high energy. They operate with different set of universal distributions, namely, the transverse momentum distributions (TMDs) and collinear distributions. However, these distributions are not entire independent. In the regime of large transverse momentum or small-b (where b is a Fourier conjugated parameter to the transverse momentum), TMDs can be factorized in the terms of collinear distributions. This relation is often refereed as ``matching relation'', and is a consequence of operator product expansion. In this talk, I will present the small-b expansion for the Sivers, Boer-Mulders, worm-gear-T and worm-gear-L functions, up to next-to-leading order (NLO).
The majority of TMDs match the collinear distributions at higher twists. For that reason their consideration is cumbersome.
The usage of the matching relation is very important for the phenomenology. It allows to incorporate the already known functions into TMDs, and in this way, reduces the parametric freedom of TMD.
Recent results on heavy quarks and quarkonia in small systems at the LHC will be reviewed. Comparison with model calculations will be shown when possible.
We present unquenched correlator data and corresponding reconstructed spectral functions for quarkonium. Correlators are obtained using clover-improved Wilson fermions on $N_f=2+1$ HISQ lattices. Valence quark masses are tuned to their physical values by comparing the mass spectrum obtained from the lattice QCD with experimental values. For the spectral reconstruction, we use models based on perturbative spectral functions from different frequency regions like resummed thermal contributions around the threshold from pNRQCD and vacuum contributions well above the threshold. We show preliminary results of the reconstructed spectral function obtained for the first time in our study for full QCD. In addition, we compare the results with the previous continuum extrapolated results in the quenched approximation.
Recent experimental results on the production of open heavy flavour mesons and quarkonium states in association with other heavy particles will be presented and discussed on behalf of the LHC experiments.
This includes the production of D meson pairs and of triple-J/psi final states as well as the production of J/psi in association with heavy vector bosons, and their interpretation in terms of multi-parton interactions. Resonance structures in J/psi pair production will also be investigated.
Quarkonium suppression is one of the more useful observables to obtain information about the hot medium created in ultrarelativistic heavy-ion collisions.
In this talk, we discuss a simple way to implement both the initial-state effects and the hot-medium evolution, and to compute the quarkonium nuclear modification factor if the survival probability for a bound state at a given energy density is known.
Based on the Glauber model, the temperature of the evolving medium and the centrality dependence of the nuclear modification factor will be analysed.
Local Unitarity provides an order-by-order representation of perturbative cross-sections that realises at the local level the cancellation of final-state collinear and soft singularities predicted by the KLN theorem. The representation is obtained by manipulating the real and virtual interference diagrams contributing to transition probabilities using general local identities. As a consequence, the Local Unitarity representation can be directly integrated using Monte Carlo methods and without the need of infrared counter-terms. I will present first results from this new approach with examples up to N3LO accuracy. I will conclude by giving an outlook on future generalisations of the method applicable to hadronic collisions.
High-precision calculations are an indispensable ingredient to the success of the LHC physics programme, yet their poor computing efficiency has been a growing cause for concern, threatening to become a paralysing bottleneck in the coming years. We present a set of solutions to reduce the Monte Carlo footprint, focusing on the current cost-driving components: the evaluation of parton-distribution functions and the perturbative matrix elements. We show that for crucial samples, such as weak boson+jets as well as top-quark-pair production, these components dominate the overall run time by up to 80%. Focusing on improvements in LHAPDF and SHERPA, in particular in the unweighting step of the MC event generation, we reduce the computing times by factors of around 50 thereby paving the way towards affordable state-of-the-art event simulation in the HL-LHC era. Furthermore we give an outlook of next steps that can even further accelerate MC event generation and thereby facilitate even more precise computations.
This presentation discusses the current status of the reengineering of the Madgraph5_aMC@NLO (MG5aMC) event generator to speed it up and port it to new architectures. The calculation of matrix elements (MEs), which constitutes the computationally intensive part and was previously handled by a scalar Fortran implementation on CPUs, is now offloaded to new implementations using event-level data parallelism with lockstep processing on CPUs (via C++ vectorization) and GPUs. Large overall speedups are thus achieved, while maintaining the look-and-feel of the existing user interface. This approach is not specific to MG5aMC, and could be efficiently exploited in any other ME Monte Carlo event generator. Development efforts are now focusing on the preparation of an upcoming alpha release of the software for the LHC experiments, supporting leading-order QCD processes. In parallel, further performance improvements are also being pursued, including the possible port of the QCD color algebra calculations to GPU tensor cores or their execution in single floating-point precision.
We discuss the recent and ongoing developments with respect to the use of machine learning methods in modeling hadronization within event generators.
This talk presents recent data from ATLAS, CMS and LHCb that is sensitive to the proton parton distribution functions (PDFs), including inclusive W and Z boson production, ttbar production, W+jets and Z+jets production, inclusive jet production and direct photon production. The data are used in combination with deep-inelastic scattering data from HERA to extract the PDFs themselves, together with a full assessment of the uncertainties.
Theory predictions play a crucial role in PDF fitting.
In order to include data for new processes, you need predictions to compare with. To assess the impact of the perturbative series, Standard Model parameters, or other external inputs, different options have to be readily available. Moreover, to do this and other studies, theory have to be recomputed over and over, with a non-negligible computing cost. This limits and delays the overall progresses.
Thus, we are developing a new framework to produce all theory components in a reproducible and fast way. We provide separate building blocks, specifically designed to be part of the whole pipeline, but developed and operating separately, in order to enhance modularity and reusability.
They are released and developed publicly, to serve as many users as possible, and collect their feedback and requests.
Parton Distribtions Functions (PDFs) are a pivotal input in every theoretical prediction involving initial-state protons, from hadron collider to neutrino telescopes. These objects are usually determined throught fits to experimental data, leaving a large degree of freedom in the choice of the best functional form to be used and in the starting energy reference scale.
In this talk we discuss the first fully data driven test of a PDF parametrisation inspired by fundamental distributions in quantum statistics [Franco Buccella et al J. Stat. Mech. (2019) 073302]. We will show the results of our fit to the PDFs using the HERA collider dataset with the \textt{xfitter} collaboration framework and then compare the overall fit performance against the HERAPDF parametrization.
We study inclusive dijet production in deep inelastic scattering at NLO within the Color Glass Condensate effective field theory. We begin by studying this process in general small-$x$ kinematics. We first show that the differential cross-section is infrared and collinear safe. We demonstrate the factorization of large rapidity logarithms that can then be resummed via JIMWLK renormalization, and we extract the NLO impact factor for which we provide explicit expressions.
We then specialize in the transverse back-to-back kinematics 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 $N_c$. We show that small-$x$ and Sudakov resummation can be performed simultaneously provided that the small-$x$ evolution of the WW distribution, formulated in terms of the projectile rapidity, is amended by a kinematic constraint that imposes lifetime ordering of successive gluon emissions. We also comment on non-logarithmically enhanced terms in the impact factor that can break TMD factorization at NLO in the saturation regime.
Refs:
[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
We report on recebt theoretical results on 3-loop anomalous dimensions and massless ans massive Wilson coefficients in the unpolarized and polarized case.
We study the prompt single and double J/ψ hadroproduction in the Improved Color Evaporation Model using the Parton Reggeization Approach. We make calculations in a single manner to described the experimental data for prompt J/ψ transverse momentum spectra from the energy of $\sqrt{s}=19$ GeV up to modern energy of the LHC, $\sqrt{s}=13$ TeV. The numerical calculations are doing using parton-level MC generator for kT−depended initial-state partons, KaTie. We use the modified KMR-type unintegrated parton distribution functions of Reggeized gluons and quarks with exact normalization based on Kimber-Martin-Ryskin-Watt model. We suggest improvement of the ICEM for the pair-production of J/ψ. In case of double J/ψ production we investigate the relative contributions of the single-parton scattering and double-parton scattering mechanisms.
Quarkonium has been used as an important probe of the quark-gluon plasma in heavy ion collisions. With more precise experimental measurements of quarkonium production conducted at RHIC and LHC, we are able to learn in a more quantitative way how quarkonium interacts with the hot medium. In this talk, I will review the framework of coupled Boltzmann equations to describe quarkonium production in heavy ion collisions. The coupled equations describe both open heavy quark transport and quarkonium dissociation and recombination in a consistent way. I will also show phenomenological results for bottomonium production and compare with recent experimental measurements.
Experimental searches for the odderon and related topics in diffractive physics are discussed.
I will discuss new higher-order photon induced mechanisms which lead to
asymmetry for $p p$ and $p \bar p$ scattering. The effect
will be discussed in the context of recent asymmetry
between the original $D0$ data for $p \bar p$ at $\sqrt{s}$ = 1.96 GeV
and the $p p$ quasi-data obtained by extrapolation form real LHC data.
I will try to answer the question whether such a mechanism can replace
the soft odderon exchange which was proposed recently to explain
the current data.
I will discuss also some other reactions where the odderon exchange may
occur. I will propose some reactions that are potentially attractive
and feasible experimentally at the LHC.
The discussion will be in the broad context of the papers known
from the literature.
While perturbation theory offers an impressive machinery to describe the strong interaction at
high energy, it is not reliable anymore to take into account long-distance degrees of freedom of the theory. Lattice QCD is a well-established approach to solve QCD from first principles of quantum field theory. Theorists have realised significant breakthrough in the recent past in topics which were considered as particularly challenging and. We are in pretty good position to understand the dynamics at work in systems under close investigation at the LHC. In this talk I will illustrate the statement by sketching a couple of recent advances in spectroscopy, hadron structure and QCD at finite temperature.
In this talk I will review the recent efforts in improving the logarithmic accuracy of the resummation encoded in parton shower algorithms, which are fundamental tools to perform collider phenomenology across a broad class of processes and observables.
This talk will be a brief overview of recent developments in event generation, with a focus on the interplay beween high-precision QCD perturbation theory and parton-shower resummation. It will also touch on topics beyond LHC.
Recent results of general searches for BSM physics within the ATLAS experiment.
Polarization of vector bosons started to become an extensively investigated topic in recent years due to its sensitivity to the concrete mechanism of electroweak symmetry breaking and to beyond standard model physics. The general-purpose Monte-Carlo event generator Sherpa is used for event simulation of various processes in the analysis of LHC data. In this talk, an implementation is presented which will enable the simulation of polarized cross sections for vector bosons in future releases of Sherpa. Special features are discussed including the simulation of all polarized contributions in a single run and the direct calculation of the interference between them. Validation data comparing the new implementation with literature studies and results from its first applications in phenomenological analyses will be shown for several processes.
In the Standard Model (SM) of particle physics, four-top-quark production is an extremely rare process with a cross section of approximately 12 fb. In extensions of the SM with top-philic new states, the four-top production rate can be enhanced considerably. In this contribution results will be presented of searches by the ATLAS and CMS experiments that have yielded the first evidence for the SM process, as well as stringent bounds on more exotic production mechanism of the same final state. The talk will address a review of the latest results of the SM 𝒕𝒕̅𝒕𝒕̅ searches at ATLAS and CMS. The results of the BSM 𝒕𝒕̅𝒕𝒕̅ searches at ATLAS will be discussed as well.
In this contribution I will describe a method to perform multi-dimensional paramtric integrations by fitting a neural network to integrand data. THis method can be applied to many areas in QCD, from phase-space integration to multi-loop integrals.
An accurate determination of the Standard Model parameters is essential for both testing the theory and discovering signals of new physics. One of them is the W boson mass, which can be extracted with great precision by measuring W/Z bosons productions rates at hadron colliders.
In this talk, I will consider transverse-momenta spectra at low- and intermediate-qT region. Large logarithmic contributions, due to soft and collinear emission, are evaluated and resummed at all orders through the well-established resummation formalism. A matching procedure is also implemented in order to obtain uniform accuracy until the high-pT region, in which cross sections are correctly computed through the conventional fixed-order perturbative series.
Although the dominant contributions to the differential cross sections are due to QCD, already known in literature until N3LL+NNLO, the consideration of EW interaction becomes essential to reach the sub-percent level of precision, i.e. the current accuracy of experimental data.
In our work, specifically, we computed EW corrections including up to NLL+NLO terms, and inserted them in a numerical code.
During the discussion, I will show some significative plots at typical LHC, Tevatron and FCC-hh configurations, focusing on the shifts and behavior-changes caused by electroweak interactions. These modifications, in particular, affects directly the W boson mass determination.
This presentation will report recent measurements on Higgs pT distributions from ATLAS and CMS experiments.
In the past few years, remarkable progresses in multi-loop calculations have opened the doors to the computation of massless two-loop five-point scattering amplitudes, allowing to complete NNLO QCD predictions for complicated $2 \rightarrow 3$ processes like tri-photon, tri-jet and di-photon plus jet production. Very recently, also the two-loop five-point scattering amplitudes with one external massive leg have been made available in literature.
Due to these successful progresses in multi-loop computations, it is reasonable thinking that also two-loop amplitudes with several massive legs will be accessible in the next future, allowing to complete NNLO QCD computations for processes with massive final-state particles.
In this talk we will discuss about recent progresses in NNLO QCD computations for processes where a heavy-quark pair is produced in association with a massive boson.
In this talk we present results for soft gluon threshold resummation applied to the production of four top quarks. Current theoretical predictions include next-to-leading (NLO) strong and electroweak corrections, yielding a relatively large associated systematic error. By considering the matching of the next-to-leading logarithmic (NLL) result to the available NLO result, we achieve NLO+NLL$^\prime$ precision for the total cross section, which in addition to logarithmic terms also takes into account $\mathcal{O}(\alpha_s)$ non-logarithmic terms that do not vanish at threshold. The threshold-resummed result shows an improved scale dependence when compared to the fixed-order calculation.
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.
An overview of recent results on open heavy flavour production in small systems at the LHC will be presented. Comparisons with model calculations will be discussed.
The behaviour of quarkonia and open-heavy flavour hadrons in hadronic collisions provide a unique testing ground for understanding quantum chromodynamics (QCD). Although there has been significant progress, our understanding of hadronic collisions has been challenged by the observation of intriguing effects in high-multiplicity proton-proton and proton-Pb collisions, such as the discovery of correlations and the suppression of quarkonium excited states in those systems. Those phenomena show a smooth continuation of heavy-ion features to small systems and lower density, whose origin is still not clear. Two serious contenders remain today as possible explanations, one based on initial-state correlations and another that requires final-state interactions to be at play.
In this talk, I will present different results, considering the possibility of final-state interactions for the explanation of quarkonium excited states. Moreover, the structure of exotic resonances that do not trivially fit the usual quark model expectations has been a matter of intense scientific debate during the last two decades. I will show that a possible way of estimating the nature of these states is to study their behavior when immersed in QCD matter.
Recent results on conventional spectroscopy were presented, including results from ATLAS, CMS and LHCb experiments at LHC. The new results on the measurement of excited heavy baryons properties ($\Xi_c^-$, $\Xi_b^0$) and searches for new doubly heavy states ($\Xi_{bc}$), measurements of the branching fractions of $B_c^+$ meson are presented.
We present an updated global analysis of nuclear PDFs, EPPS21. As main new constraints on our fit, we include LHC proton-lead 5 TeV double-differential dijet and D-meson data, and 8 TeV W$^\pm$ data. These measurements are found to give a consistent picture of small-x shadowing and mid-x antishadowing of nuclear gluons and significantly reduce the nuclear-PDF uncertainties. In addition, we also include new DIS data from the JLab CLAS and Hall-C experiments. On the theoretical side, we have improved the analysis by propagating the baseline proton-PDF uncertainties into the extraction of the nuclear modifications and provide the tools for propagating the correlated uncertainties into any observable computable in collinear factorization.
In this contribution, an overview of the most recent measurements to constrain nuclear parton distribution functions at the LHC will be made.
Multi-parton distributions are the non-perturbative quantities needed to make predictions for multiple scattering rates. These are poorly constrained from theory and data, and must be modelled. For double parton scattering, some important theoretical constraints on the relevant distributions were derived in 2009: the momentum and number sum rules. Here we derive the corresponding sum rules for the triple parton distributions. We discuss how well the double and triple parton distributions produced by the Pythia model of MPI satisfy these sum rules, and then describe how the Pythia predictions for double Drell-Yan production via DPS compare to those obtained via other approaches, including the most naive "pocket formula" approach.
This talk gives an overview of the latest results of hadronisation studies at the LHC. The results will be discussed in comparison with various different model calculations. The talk also highlights new insights that challenge the assumption of universal parton-to-hadron fragmentation with an emphasis on heavy-flavour hadrons.
This talk covers the recent results on VBF and VBS measurements from ATLAS and CMS experiments.
Final states in collider experiments are characterized by correlation functions of the energy flow operator - which plays the roll of an idealised calorimeter. In this talk, I will show that the top quark imprints itself as a peak in the three-point correlator at an angle determined by its mass and transverse momentum. This provides direct access to one of the most important parameters of the Standard Model in one of the simplest field theoretical observables.
The analysis I will present provides a new direction for a precise top mass determination that is, for the first time, highly insensitive to soft physics and underlying event contamination.
Measurements of multiboson production at the LHC are fundamental
probes of the electroweak gauge structure of the Standard Model. With
the large data samples from the LHC, processes involving quartic gauge
boson couplings are now accessible. In this talk we present recent ATLAS
and CMS results of multiboson production at the LHC.
The kinematics reachable at the Large Hadron Collider (LHC) offer us a unique opportunity to probe the high-energy regime of QCD in quite original and unprecedented ways.
An interesting new channel, which has been proposed to investigate the semi-hard regime of QCD, is the inclusive hadroproduction of a forward Higgs boson in association with a backward identified jet.
Within the so-called Balitski-Fadin-Kuraev-Lipatov (BFKL) approach, established tool to investigate the Regge-Gribov limit of QCD, the fundamental missing ingredient for a full next-to-leading logarithimic (NLL) description of the aforementioned process, is the NLO Higgs boson impact factor (IF).
We present a full NLO result for the forward Higgs IF, obtained in the infinite top-mass limit, discussing problems associated with a high-energy computation in the presence of the Higgs effective vertex. We also present preliminary phenomenological results.
Quarkonia has been long regarded as golden probes to study the fundamental (de)confinement of Quantum Chromodynamics (QCD). Understanding their production provided crucial information for the physics on non-perturbative QCD factorization. However, the mechanism behind the production of various quarkonium states are still under investigation even after ~50 years from the discovery of the J/Psi meson in 1974, the “November Revolution”. In this talk, the recent results for inclusive quarkonium production in proton-proton collisions at the LHC, reported by the ALICE, ATLAS, CMS, and LHCb Collaborations, are reviewed and discussed in terms of production mechanism such as Colour Evaporation Model (CEM), Colour-Singlet Model (CSM), and non-relativistic QCD (NRQCD).
We present our next-to-leading order (NLO) calculation of associated hadroproduction of J/psi plus W or Z bosons within the factorization framework of nonrelativistic QCD (NRQCD). We compare to ATLAS data using various sets of nonperturbative long distance matrix elements (LDMEs) as input, thereby opening up a completely new angle in the ongoing quest to understand whether the LDMEs are universal or not. We give an overview of how these NLO universality tests now unfold after inclusion of our new results.
Based on the potential nonrelativistic QCD formalism, we compute the nonrelativistic QCD long-distance matrix elements (LDMEs) for inclusive production of S-wave heavy quarkonia. This greatly reduces the number of nonperturbative unknowns and brings in a substantial enhancement in the predictive power of the nonrelativistic QCD factorization formalism. We obtain improved determinations of the LDMEs and find cross sections and polarizations of J/ψ, ψ(2S), and excited Υ states that agree well with LHC data. Our results may have important implications in pinning down the heavy quarkonium production mechanism.
An overview of the most recent experimental results by LHCb, CMS and ATLAS collaborations of the LHC on analyses involving exotic hadrons
The review of the present status and recent developments in the theory of heavy quarkonium production in proton-proton and lepton-proton collisions will be given.
This contribution is devoted to understanding the charmonium production mechanism using data from the LHC experiment. It describes a series of recent studies of single and double quarkonium production performed by ATLAS, CMS and LHCb experiments.
Although significant results were obtained concerning quark transverse-momentum dependent distribution functions (TMD PDFs), the deep knowledge on their formal properties being surrounded by a rich and wealthy phenomenology, the gluon-TMD field represents an almost uncharted territory. After a brief introduction of gluon TMD PDFs and their connection with spin studies, we report progresses done via model-dependent calculations of T-even and T-odd functions at leading twist. We then review the potential of the LHC, including its fixed-target mode, to catch the inner dynamics of gluons inside protons via TMD studies in Higgs and quarkonium production. We also explore the possibility offered by the LHC in the fixed target mode with a polarized target.
Recent progress in the determination of nCTEQ nuclear PDFs will be discussed based on LHC heavy quark and quarkonium data putting strong constraints on the nuclear gluon PDF down to very small x ~ 10^-5.
We will also summarize the results of a recent in depth study of neutrino deep inelastic scattering data and their impact on nCTEQ nuclear PDFs.
In this contribution we summarize the role of multi parton scattering at the LHC with emphasis on the double parton scattering (DPS). In particular, the relevance of the these processes will be discussed in view of the extraction of novel information on the proton structure.
Finally, possible developments for the observation of DPS at the future EIC will be presented.
The theory of the strong force, Quantum Chromodynamics, describes the proton in terms of quarks and gluons. The proton is a bound state of two up and one down quark, but quantum theory predicts that in addition there is an infinite number of quark-antiquark pairs. Both light and heavy quarks, whose mass is respectively smaller or bigger than the proton’s, are revealed inside the proton in high-energy collisions. However, it is unclear whether heavy quarks also exist as a part of the static nucleon wave-function: so-called intrinsic heavy quarks. It has been argued for long that the proton could have a sizable intrinsic component of the lightest heavy quark, the charm quark. Innumerable efforts to establish intrinsic charm in the proton have remained inconclusive. We provide first evidence for intrinsic charm by exploiting a high- precision determination of the quark-gluon content of the nucleon based on machine learning and a large experimental dataset. We disentangle the intrinsic charm component from charm-anticharm pairs arising from high-energy radiation. We establish the existence of intrinsic charm at the 3σ level, with a momentum distribution in remarkable agreement with model predictions. We confirm these findings by comparing to very recent data on Z production with charm jets from the LHCb experiment.
Fixed-target experiments at the LHC provide opportunities to study QCD in novel collision systems and in regions of phase space inaccessible to collider experiments. These unique features make fixed-target measurements powerful for constraining parton distribution functions (PDFs) and therefore probing proton and nuclear structure. In this talk, recent measurements of heavy flavour production in the fixed-target configuration of LHCb and their potential impact on PDFs will be presented. Prospects for future measurements at the LHC with the upgraded LHCb fixed-target program and proposed ALICE fixed-target program will also be discussed.
We discuss production of neutral $D$ mesons in proton-proton collisions at the LHC fixed target mode in the framework of the BJM recombination model [1]. We present rapidity and transverse momentum distributions of $D$ mesons and compare the recombination contribution to the dominant gluon-gluon fusion mechanism. Both the direct production, as dictated by the matrix element, and fragmentation of the associated $c$ or $\bar c$ are included. The latter mechanism generates $D$ mesons with smaller rapidities than those produced directly. We calculate the $D^0 + {\overline D^{0}}$ meson distributions relevant for fixed target $p\!+\!\!^{4}\!H\!e$ collisions at $\sqrt{s}$ = 86.6 GeV as well as for $p\!+\!\!^{20}\!N\!e$ collisions at $\sqrt{s}$ = 69 GeV. The recombination component improves the description of the LHCb data and in addition results in production asymmetry. The asymmetries in $D^{0}\! \!\overline{D^{0}}$ production as a function of rapidity and transverse momentum are shown and the cancellation of terms for direct production and associated $c/{\bar c}$ fragmentation is discussed.
We discuss also production of far-forward charm/anticharm quarks, $D$ mesons and neutrinos/antineutrinos from their semileptonic decays in proton-proton collisions at the LHC energies [2]. The calculation is preformed within $k_t$-factorization and hybrid model using different unintegrated gluon distribution functions (UGDFs) from the literature. We include gluon-gluon fusion, intrinsic charm (IC) as well as recombination mechanisms. We compare our results to the LHCb data for different rapidity bins in the interval $2 < y < 4.5$. A good description is achieved for the Kimber-Martin-Ryskin UGDF. We also show results for the Kutak-Sapeta UGDF, both in the linear form and including nonlinear effects. The nonlinear effects play a role only at very small transverse
momenta of $D^0$ or $\bar D^0$ mesons. The IC and recombination models are negligible at the LHCb kinematics. Both the mechanisms start to be crucial at larger rapidities and dominate over the standard charm production mechanisms. At high energies there are so far no experiments probing this region. We present uncertainty bands for the both mechanisms. Decreased uncertainty bands will be available soon from the fixed target experiments p + A. The recombination component leads to production asymmetry for quarks ($c \ne {\bar c}$) and in consequence for mesons ($D^0 \ne {\bar D^0}$). We present also energy distributions for forward neutrinos to be measured by the forward physics facilities such as FASER$\nu$. We show results for electron, muon and tau neutrinos. Again different components are shown separately.
[1] R. Maciuła and A. Szczurek, arXiv:2206.02750 [hep-ph].
[1] R. Maciuła and A. Szczurek, a paper in preparation.
The talk discusses some developments in the resummation of colour-singlet transverse observables in momentum space, highlighting differences with respect to traditional b-space resummation. Recent results for N3LO fiducial Drell-Yan distributions are presented.
Recent results on alpha_s study in ATLAS and CMS, especially on Energy-Energy Correlation in ATLAS, and mostly jets in CMS.
Quark form factors are important building blocks for several processes studied at the LHC, for example Higgs boson production and decay as well as top-pair production. I will present our calculation of massive quark form factors at three loops in QCD including both singlet and non-singlet contributions. After reducing the Feynman integrals in the amplitudes to master integrals, these were computed by solving differential equations. By constructing expansions around regular as well as singular points and numerical matching, we obtain sufficient precision over the whole kinematic range.
The proton and nuclear gluon distribution functions show a strong
increase at low values of Bjorken x. This increase, if untamed, would
eventually lead to violation of unitarity. The growth of the gluon
distribution must therefore at some point saturate. I will review the
experimental status on saturation at the LHC.
The cross-sections of diffractive double hadron photo- or electroproduction with large pT, on a nucleon or a nucleus, are calculated to NLO accuracy.
A hybrid formalism mixing collinear factorization and high energy kt factorization, more precisely the shockwave formalism, is used to derive the results.
The cancellation of divergences is explicitly shown, and the finite parts of the NLO differential cross-section are found. We work in arbitrary kinematics such that both photoproduction and leptoproduction are considered, making the results usable in order to detect saturation at both the future EIC or already at LHC, using UPC.
Jet substructure is a powerful tool to probe the perturbative regime of jet evolution in proton-proton and heavy-ion collisions. Over the past few years, various substructure observables have been proposed to understand specific aspects of jet dynamics in a quark-gluon plasma (QGP).
In this talk, based on [1,2,3], we will explore the ability of such an observable, called Dynamical Grooming, to pin down the properties of the QGP. In particular, we will present the computation via analytic resummation techniques and Monte-Carlo simulations, of the opening angle $\theta_g$ of the hardest splitting in the jet as defined by Dynamical Grooming. This calculation, grounded in perturbative QCD, accounts for the factorization in time between vacuum-like and medium-induced processes in the double logarithmic approximation. Our main result is that the dominating scale in the $\theta_g$-distribution is the decoherence angle $\theta_c$ which characterizes the medium's resolution power to propagate color probes, which makes this observable particularly interesting to measure $\theta_c$ experimentally. To that aim, we will highlight a suitable combination of the Dynamical Grooming condition and the jet radius that leads to a pQCD-dominated observable with minimal sensitivity to the medium response.
Refs:
[1] P. Caucal, A. Soto-Ontoso and A. Takacs, JHEP07(2021)020
[2] P. Caucal, A. Soto-Ontoso and A. Takacs, Phys.Rev.D105(2022)114046
[3] J.H. Isaksen, A. Takacs and K. Tywoniuk, arXiv:2206.02811
Jets are modified as they propagate through the quark-gluon plasma, providing the opportunity to study the properties of the medium, including by measuring modification of the internal jet structure. In this talk, we discuss several recent jet substructure measurements in Pb--Pb collisions at the LHC.
The energy-flow-operator (EFO) provides an idealized field-theoretic definition of a calorimenter. Recently, the angular correlations between EFOs on the celestial sphere have seen a great deal of interest as a tool for jet substructure. Due to the causal structure of EFO correlators, the angular size of the correlations can be viewed as a time parameter: early time perturbative correlations are imprinted at large angles, whilst later time correlations from hadronization appear at small angles. In this work we demonstrate that the scales associated with the early time evolution (quenching) of a jet propagating through the QGP are imprinted in the large-angle perturbative structure of the 2-point correlator.
The field of jet quenching in heavy ion collisions has been steadily moving towards the description and measurement of jet substructure observables. From a theoretical point of view, the main ingredient to understand how jets evolve inside a medium is still missing: a full evaluation of the in-medium parton splitting with an arbitrary number of scatterings and finite energy fraction. In this talk we summarize previous approximations used to calculate these splittings and provide a method for its full evaluation.
In this study, I am going to present the development of photoproduction at NLO in the fixed-order mode of MadGraph5_aMC@NLO where the photon is either coming from an electron or from a proton in an ultra-peripheral collision at the LHC. In addition, I will also present the development for asymmetric hadron collisions in order to provide predictions e.g. for proton-nucleus collisions
An overview of the recent results from ALICE, CMS and LHCb on the exclusive quarconium production will be presented.
We present the first study of coherent exclusive J/psi photoproduction in ultraperipheral collisions (UPCs) of heavy and intermediate ions at the LHC in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD and make predictions for the J/psi rapidity distributions for the cases of lead (Pb) and oxygen (O) beams. We confirm the general expectation of a dramatic role of NLO corrections, quantify the significant uncertainties associated with used nuclear PDFs and the choice of hard scale, and determine an "optimal scale" allowing for a simultaneously good description of all available Run 1 and Run 2 LHC data on J/psi photoproduction in Pb-Pb UPCs. One of the major results of our study is the counter-intuitive observation that at central rapidities,
the cross section is dominated by the quark contribution since the gluon one largely cancels in the sum of the (leading-order) LO and the NLO terms. To better control the theoretical uncertainties, we advocate the use of the ratio of UPC cross sections on oxygen and lead, for which we make detailed predictions.
While hadronic structure is experimentally probed by processes such as DIS and
DVCS, both lattice and continuum techniques are employed to corroborate such re-
sults from a theoretical perspective. On the continuum side, the Fadeev equations
provide a fully covariant approach to three body interactions convenient for describing
three quark hadronic states. However, the four-spacetime-dimensional nature of the
corresponding Fadeev wave functions precludes a probabilistic interpretation, encour-
aging our use of their 3-spacetime-dimensional light cone projections, Light Front Wave
Functions (LFWFs). An intuitional advantage of LFWFs is their role as coefficients
in Fock expansions of hadronic states. We first define nucleon Fadeev wave functions
in terms of off-diagonal nucleon matrix elements, and subsequently express the cor-
responding definite orbital angular momentum (OAM) nucleon LFWFs. With these
definite quark helicity LFWFs in hand we calculate GPDs as linear combinations of
their overlaps, and isolate definite OAM contributions to nucleon GPDs, PDFs, Form
Factors (FFs) and the electric nucleon radius. Looking forward, this work will allow
us to map dynamical effects underlying the computation of Fadeev wave functions to the multimensional structure of the nucleon.
In this talk, we present the next-to-next-to-leading-order (NNLO) subtraction formula for local cancellation of infrared (IR) divergences for final-state radiation in massless QCD, applying to generic IR-safe observables. Such general and automated algorithm has been developed within the framework of Local analytic sector subtraction. We explicitly show the features of the method and investigate a comprehensive treatment of singularities, which is ultimately necessary to ensure the locality of the subtraction. After performing the counterterms integration, we analytically verify the cancellation of the explicit $\epsilon$ poles coming from the double-virtual contribution for processes with an arbitrary number of final-state partons, thus obtaining as a final result a compact (as well as analytic) finite remainder and a formula suitable for direct numerical implementation, paving the way to further validations and the production of relevant phenomenological results.
I will present the latest results form the ATLAS and CM experiments about photon production measurements at the LHC
Availability of NNLO QCD predictions for scattering processes such as Vjj and Hjj production is essential for the ongoing physics program at the LHC. A crucial missing ingredient is the Feynman integrals contributing to double virtual corrections. In this talk we present the complete set for the relevant two-loop five-point integrals with one external mass and the associated basis of special functions.
Employing the method of canonical differential equations and the properties of logarithmic iterated integrals, we construct the basis that will greatly facilitate the calculation of needed two-loop scattering amplitudes, and is amenable for immediate phenomenological applications.
The weak mixing angle is a key parameter in the electroweak sector of the standard model. Precision measurements of the weak mixing angle allow for testing the standard model and for searching for the effects of new physics.
Since jets are highly non trivial objects it is a delicate problem to meaningfully assign a flavor label to them. We show that modern jet substructure techniques can give us new ways to tackle this problem.
We propose two different approaches. On the one hand, we introduce a novel fragmentation-function framework that allows one to connect a flavor definition in the deep UV, where partons live, to an IR definition, where jets live. The IR definition involves the Winner-Take-All axis and it has the advantage that the resulting evolution equations are linear. On the other hand, we consider the issue of interfacing measurements involving flavored jets (typically heavy-flavors) with precision calculations in QCD. We introduce a jet-flavor algorithm, based on Soft Drop grooming, which is at the same time IRC safe through NNLO and easy to implement in experimental analyses.
We present a measurement of the jet mass distribution in fully hadronic decays of boosted top quarks with full Run 2 data. The measurement is performed in the lepton+jets channel of top quark pair production. The top quark decay products of the all-hadronic decay cascade are reconstructed with a single large-radius jet with transverse momentum greater than 400 GeV. The top quark mass is extracted from the normalised differential top quark pair production cross section at the particle level. The uncertainties arising from the calibration of the jet mass scale and modelling of the final state radiation in simulation are improved by dedicated studies of the jet substructure. These studies lead to a significant increase in precision in the top quark mass with respect to an earlier measurement, now reaching a precision below 1 GeV.
We present a state-of-the art computation for forward dijets in proton-proton and proton-lead collisions at the LHC, using the kinematics of FCal ATLAS calorimeter and the planned FoCal extension of ALICE. We use the small-$x$ improved TMD (ITMD) formalism, together with collinearly improved TMD gluon distributions, full $b$-space Sudakov resummation
and discuss nonperturbative corrections due to hadronization and showers using the \Pythia\ Monte Carlo. We observe that forward dijets in proton-nucleus collisions at moderately low $p_T$ are excellent probes of saturation effects, as the Sudakov resummation does not alter the suppression of the cross section.
This talk will describe BSM searches with jet substructure in Atlas, CMS, and LHCb experiments. It will be focus on the newest results from full-RunII analysis exploiting the state of the art tecquinques that allow to identify the internal structure of jets stamming from decay cascades of heavy particles like Vector bosons, Higgs bosons, Top quarks that exhibit a large Lorentz boost in the detector rest frame. Such topologies are typical of new physics signatures, and therefore efficient and accurate identification of such boosted candidates is crucial to LHC physics program in order to discover hints of New Physics.
We review the status of flavour anomalies and discuss the theoretical predictions for the observables of interest. Comparing these predictions with the current experimental measurement, we discuss possible beyond the standard model scenarios which can accommodate these anomalies.
Over the last decade, measurements of $b\rightarrow s \ell^+\ell^-$ and $b\rightarrow c \ell^+\nu$ transitions have consistently shown tensions with Standard Model predictions. These tensions are referred to collectively as the Flavour Anomalies. In this talk, an overview of the Flavour Anomalies will be given, with a particular focus on the experimental challenges surrounding these measurements, in addition to a discussion on Run 3 prospects.
Ten years after the Higgs boson discovery, this talk presents a summary of the measurement of the particle's properties, in the journey to disclose its nature.
We present a formalism that sums up the soft-virtual (SV) and next-to-SV (NSV) diagonal contributions
to inclusive production of colorless particle in hadron colliders to all orders in perturbative QCD.
We use the factorization theorem and renormalization group invariance as well as employing the transcendental structure of perturbative results to obtain the resummed result. Using this we predict certain SV and NSV terms to all orders from lower order information. We also present an integral representation for the coefficient functions that is suitable for Mellin N-space resummation. The phenomenological
impact of our results on Drell-Yan and Higgs productions at the LHC is discussed.
Fixed-order predictions are one of the pillars of precision particle physics. In the talk, I will review some of the latest developments in calculating higher-order perturbative corrections to well-studied processes at colliders and highlight the difficulties that have been overcome to provide accurate theoretical predictions.
Distribution (possibly to eat quickly)
Boats at 14h30, 15h00, 15h30, 16h00, 16h30,17h00
Upon registration (50€).
We report on recent progress for the QCD corrections to top-quark pair plus jet production. In particular, we discuss a recent computation for the two-loop master integrals associated to a two-loop five-point pentagon-box integral configuration with one internal massive propagator, that contributes to top-quark pair production in association with a jet in the QCD planar limit.
In this talk, I will present a calculation of the two-loop mixed QCD-electroweak amplitudes for Z+jet production in proton colliders. I will argue that employing a recently proposed projector method reduces the amount of independent Lorentz tensor structures, even for anomalous contributions. I will discuss the numerical evaluation of multi-scale Feynman integrals with the Auxiliary Mass Flow method. Finally, I will mention potential applications to Dark Matter searches at the LHC.
The top quark is produced at the LHC in pair with its anti-particle via strong interactions and singly via electroweak interactions. An accurate knowledge of its production cross section can bring key information on fundamental interactions at the electroweak symmetry-breaking scale and beyond.
The talk will cover latest results on differential measurements of top and top pair production.
In my talk, I will present precision predictions for the production of scalar leptoquarks at the LHC, evaluated at next-to-leading order in QCD and improved by the resummation of soft-gluon radiation at next-to-next-to-leading-logarithmic accuracy. Apart from QCD contributions, included are the lepton $t$-channel exchange diagrams relevant in the light of the recent $B$-flavour anomalies. The results exhibit an interesting interplay between the different contributions, affected considerably by the choice of parton distribution functions, and the net effect on a cross section turns out to be very non-generic for a variety of benchmark scenarios favoured by the anomalies. These predictions consist of the most precise leptoquark cross section calculations available to date and are necessary for the best exploitation of leptoquark LHC searches.
We study the influence of theoretical systematic uncertainties due to the quark density on LHC experimental searches for Z'-bosons.
Using an approach originally proposed in the context of the ABMP16 PDF set for the high-x behaviour of the quark density, we presents results on differential cross section and Forward-Backward asymmetry observables commonly used to study Z' signals in dilepton channels.
In this talk, I discuss the scalar Leptoquark pair production at the Large Hadron Collider (LHC) at next-to-leading order in QCD including contributions of diagrams involving the exchange of leptons in the $t$-channel. In this work, we discuss not only the so-called on-diagonal channels that involve same-mass eigenstates but also off-diagonal channels that include different mass eigenstates. We found that for moderate to large values of the Yukawa type leptoquark-quark-lepton couplings, the off-diagonal channels dominate over the on-diagonal channels. I comment on the size of the off-diagonal channel contributions in viable scenarios addressing the flavour anomalies.
We discuss the sensitivity of theoretical predictions for observables used in searches for new physics to current knowledge, or lack thereof, of parton distribution functions (PDFs) at large momentum fractions. We specifically consider the neutral-current Drell-Yan production of gauge bosons with invariant masses in the TeV range. We study the forward-backward asymmetry of charged leptons from the decay of the gauge boson in its rest frame, a traditional probe of new physics: we demonstrate that its qualitative behavior strongly depends on the behavior of the PDFs. We discuss and compare the large-x behavior of different PDF sets, and find that they differ significantly. Specifically, the behavior observed at lower invariant masses, common to all PDF sets, is not necessarily reproduced at large masses if unbiased PDFs are used. It follows that deviations from it cannot be taken as an indication of new physics. We show that forward-backward asymmetry measurements could help in pinning down the PDF uncertainty at large momentum fractions and discuss the accuracy that would be required in order to enable searches for new physics that rely on knowledge of PDFs in this region.
(Abstract submitted on behalf of the NNPDF Collaboration, speaker will be indicated at a later stage)
Results are presented from measurements of light and heavy jets in Pb+Pb and p+Pbn collisions
The formalism of Baier-Dokshitzer-Mueller-Peigné-Schiff and Zakharov determines the modifications of parton splittings in the QCD plasma that arise from medium-induced gluon radiation. Here, we study medium-modifications of the gluon splitting into a quark--anti-quark pair in this BDMPS-Z formalism. We derive a compact path-integral formulation that resums effects from an arbitrary number of interactions with the medium to leading $\mathcal{O}(1/N_c^2)$. Analyses in the $N=1$ opacity and the saddle point approximations reveal two phenomena: a medium-induced momentum broadening that increases the invariant mass of quark--anti-quark pairs, and a medium-enhanced production of such pairs. We note that both effects are numerically sizeable if the average momentum transfer from the medium is comparable to the quark mass. In ultra-relativistic heavy-ion collisions, this condition is satisfied for charm quarks. We therefore focus our numerical analysis on the medium modification of $g\to c\bar{c}$, although our derivation applies equally well to $g\to b\bar{b}$ and to gluons splitting into light-flavoured quark--anti-quark pairs.
QCD factorization allows us to model the jet energy-loss in A-A collisions as a convolution between the jet cross section in p-p collisions and an energy loss distribution. Meanwhile, Bayesian inference provides a data-driven way of constraining the energy loss distribution parameterization. Only a few efforts have been made in this direction, and solely using untagged jets. However, gluon and quark jets are known to loose energy differently. By discriminating them, we distinguish the energy loss distributions of each parton-jet and arrive at a different set of parameters for each. This allows for a more universal model that can be used for prediction in other jet measurements where quark/gluon ratio is different. A form for the energy loss distribution is chosen in the soft scattering approximation and the Markov Chain Monte Carlo method is then employed to estimate the parameters. The jet suppression obtained from the extracted energy loss distribution for inclusive jets show good agreement with measured one. However, it is sensitive to the collision energy. This might be caused by a poor constraining power of only relying on inclusive jets. We show the improvement by including photon tagged jets to the analysis.
With this study, we hope to achieve a better and more constrained modeling of the jet energy loss distribution, as well as to retrieve insights on how current theoretical models can improve by adding more insight from measurements.
By colliding heavy nuclei at ultrarelativistic energies in the Large Hadron Collider (LHC), the quark-gluon plasma (QGP) -- a hot and dense medium in which partons are deconfined -- is created. The properties of this new state of nuclear matter can be characterized, in particular, by studying low momentum (or "soft") particles (which constitue the majority of the created particles) and the physical processes involved in their production.
This presentation will highlight a set of measurements of the soft probes at the LHC.
In this work, we start by exploring the scaling features in the jet quenching parameter ($\hat{q}$) among the static and Bjorken expanding medium profiles for pure radiation and momentum broadening cascades respectively. Additionally, we investigate the early and late onset of the initial quenching time for the Bjorken expanding profile. Next, we solve the radiation only dependent in- medium gluon evolution equations by the Markov chain Monte- Carlo algorithm MINCAS followed by the study of the transverse momentum only dependent gluon emission spectra in an expanding medium. We investigate the role and the validity of the scaling laws obtained from radiation and momentum broadening for the numerical solutions of the evolution equation. We find that expanding medium profiles lead to relatively weaker transverse momentum broadening compared to expectations from static medium, which could impact the phenomenogical description of out-of-cone radiation and jet quenching.
This talk is expected to show the machine-learning techniques applied in tagging boosted jets in ATLAS and CMS experiments. Jet deep tagging, taking also into account the jet substructure, focuses on the identification of heavy particles decaying in boosted jets.
Identifying the flavour of reconstructed hadronic jets is critical for precision phenomenology and the search for new physics at colliders, as it allows to pinpoint specific scattering processes and reject backgrounds. We propose a new approach to define the flavour of jets, a flavour dressing algorithm, which is infrared and collinear safe and can be combined with any definition of a jet. We test the algorithm in $e^+e^-$ and $pp$ environments, and consider some practical applications at the LHC.
High Energy Jets (HEJ) is a resummation framework designed to include contributions from high energy logarithms in $\hat{s}/p_\perp^2$ to all orders in perturbation theory. These logs can become significant at the LHC and future colliders, and are significantly enhanced by the requirement of a large dijet invariant mass or large rapidity separation common in VBF/VBS cuts.
I will present a general overview of the HEJ formalism at leading logarithm, followed by a discussion on recent developments included as part of the upcoming code release. In particular, I will discuss predictions for the QCD $\mathcal{O}(\alpha_W^2\alpha_s^2)$ contribution to same-sign $WW + \geq 2$ jets vector boson scattering [arXiv:2107.06818] and for inclusive Higgs + 1 jet production [preprint Sept 2022].
We present a study of Higgs interference effects for the ttbar decay mode at NLO QCD in the 1-Higgs-singlet extension of the Standard Model. Results for stable tops are presented. The interference effects have been studied for different benchmark points with heavy Higgs masses in the range 700--3000 GeV. For this purpose a new Monte Carlo framework has been developed. This has made it possible to study the interference effect between tree-level and loop-induced processes at NLO, and can easily be generalised to work for any loop-induced process.
In addition, I will present H1jet, a fast and easy-to-use program that computes the differential distribution in the transverse momentum of a colour singlet. H1jet can be used by theorists to quickly assess deviations of selected new physics models from the Standard Model behaviour, and quickly obtain distributions of relevance for Standard Model phenomenology.
Given the absence of clear New Physics signals, Effective Field Theories (EFTs) are being exploited to provide model-independent descriptions of phenomena lying at energies above current direct reach. Interpreting measurements under these extended frameworks often requires complex likelihood fits of multidimensional phase spaces. In this talk we highlight some of the techniques currently being explored and/or applied to address challenges arising from the difficulty in constraining the entire phase space, from correlations existing between the coefficients being fitted, and from intractable likelihood functions. We focus on Standard Model EFT, but also cover other EFT types.
We assess the impact of the full luminosity LHC Run II top quark measurements on global PDF and SMEFT analyses as well as on their mutual interplay.
Starting from the widest LHC top quark dataset considered to date, we first assess the constraints it provides on the gluon PDF in the NNPDF4.0 framework and study its consistency with other gluon-sensitive measurements.
We then carry out an extensive SMEFT interpretation of the same dataset to provide bounds on more than 20 Wilson coefficients, demonstrating the significant new information provided by Run II measurements.
Subsequently we combine the two analyses within the SimuNET approach to achieve a simultaneous extraction of the SMEFT PDFs and the Wilson coefficients from the LHC Run II top quark data and identify the regions of the parameter space where their interplay is most phenomenologically relevant.
We also propose strategies to separate EFT corrections from QCD effects in the interpretation of the LHC top quark data.
The DGLAP equations describe how parton distribution functions evolve between different energy scales. In this talk, we will discuss how potential effects of New Physics, parametrised in terms of higher dimensional operators in the Standard Model Effective Field Theory, could affect these equations. We assess the importance of the dimensionality of the operators and the role that it plays in the calculation of the DGLAP splitting functions in the collinear limit.
Photons are radiated during all stages of heavy-ion collisions, including from the hot and dense quark-gluon plasma (QGP). In this talk, we consider the polarization of these QGP photons. The polarization, albeit difficult to measure, gives detailed information about how the anisotropy of the QGP medium evolves and thus how the medium isotropizes during the initial stages of collisions. We evaluate for the first time the emission of polarized photons through bremsstrahlung and quark-antiquark pair annihilation in an anisotropic QGP medium, including the Landau-Pomeranchuk-Migdal effect fully. We then show that the polarization goes directly as the anisotropy of the soft gluon cloud radiated by quarks and gluons. Finally, we discuss the size of photon polarization in LHC experiments, feasibility of measuring it and implications of our work for dileptons.
Various features of quantum chromodynamics (QCD) are an essential part of the phenomenology of the events at hadron colliders, such as the LHC, including soft and non-perturbative features. In order to constrain the parameters of models of soft QCD, diverse measurements are provided by the ALICE, ATLAS and CMS collaborations. Particle production mechanism including the underlying event activity at LHC is explored in this talk.
We evaluate the longitudinal or (chromo-)electric Yang-Mills gluon propagator in the recently proposed center-symmetric Landau gauge at finite temperature. To model the effect of the Gribov copies in the infrared, we use the Curci-Ferrari model which, in turn, allows us to rely on perturbative calculations. At one-loop order in the SU(2) case, the so-obtained longitudinal gluon propagator provides a clear signature for Z2 center-symmetry breaking with a singular behavior, characteristic of a continuous phase transition. This is in sharp contrast with what is found within the standard Landau gauge. We also identify various signatures for Z3 center-symmetry breaking in the SU(3) case in the form of genuine order parameters. Among those, we find that the gluon propagator, although degenerate along the diagonal color directions in the confining phase, becomes non-degenerate in the deconfined phase. Our results open new ways of identifying the transition from correlation functions both within continuum approaches and on the lattice.
This talk shows the studies about open heavy flavor, quarkonia, Z and W in PbPb collisions in ALICE, ATLAS, LHCb, CMS experiments.
I will discuss recent measurement of the dead cone effect using jet substructure, recent theoretical calculations, and prospects for using the effect in heavy ion collisions to isolate medium-induced radiation.
This talk will cover recent measurements of jets and their substructure by ALICE, ATLAS, CMS, and LHCb.
In this contribution, I will present selected recent measurements from heavy-ion collisions at the LHC that help us characterize the quark-gluon plasma created in these collisions. Limits of its formation will be discussed with the support of similar measurements performed in pp and p-Pb collisions.
We propose a brief overview of various generalizations of the usual parton distributions. These provide multidimensional pictures of the hadron internal structure and allow one to probe the orbital angular momentum content. We mention some of the recent progress and discuss the relevance of these objects for the LHC.
The Future Circular Collider (FCC) is a post-LHC project aiming at direct and indirect searches for physics beyond the SM in a new 90-km tunnel at CERN. Running in its first phase as a very-high-luminosity electron-positron collider in the range of center-of-mass energies $\sqrt{s} =90-$350 GeV, the FCC-ee will offer unparalleled physics opportunities for precise measurements of QCD phenomena in a very clean environment through, literally, billions of hadronic final states. The FCC-ee perspectives for (i) permillle extractions of the strong coupling $\alpha_S(m_Z)$ via multiple observables, (ii) high-precision analyses of parton radiation and jet fragmentation, as well as (iii) detailed studies of non-perturbative QCD (hadronization, color reconnection,...) will be summarized.