Welcome to DIS2017. This is the 25th in a series of International Workshops covering an eclectic mixture of material related to Quantum Chromodynamics and DIS as well as a general survey of the hottest current topics in high energy physics. Much of the program is devoted to the most recent results from large experiments at BNL, CERN, DESY, FNAL, JLab, and KEK. Relevant theoretical advances are also covered in detail.
The conference proceedings are published on-line by PoS. For details, see https://indico.cern.ch/event/568360/page/8375-proceedings
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Additional details at dis17.org. Hosted by The University of Birmingham
With top quark physics now entering the precision era, the need for ever more accurate theory calculations is greater than ever. In this talk we present a formalism, derived from SCET, for the simultaneous resummation of soft and small mass logarithms present in top quark pair production at the LHC. By matching with standard soft gluon resummation and recent exact NNLO results, we present differential cross sections of the pair invariant mass and top quark transverse momentum which are applicable to the entire phase space with an accuracy of NNLO+NNLL' . Finally, we will also comment on the choice of factorisation scale and on comparison with experimental data.
Measurements of the inclusive and differential top-quark pair cross sections in proton-proton collisions at both 8 and 13 TeV with the ATLAS detector at the Large Hadron Collider are presented. The inclusive measurements reach high precision and are compared to the best available theoretical calculations. Differential measurements of the kinematic properties of the top quark production are also discussed. These measurements, including results using boosted tops, probe our understanding of top quark pair production in the TeV regime. The results, unfolded to particle and parton level, are compared to Monte Carlo generators implementing LO and NLO matrix elements matched with parton showers and NNLO QCD calculations.
Measurements of the inclusive and differential top quark pair production cross section via the strong force at 7 TeV, 8 TeV and 13 TeV are presented, performed using CMS data collected in 2011, 2012 and 2015. The total cross section is measured in the lepton+jets, dilepton and fully hadronic channels, including the tau-dilepton and tau+jets modes. Indirect constraints on both the top quark mass and $\alpha_{s}$ are obtained through their relation to the inclusive cross section. First measurements of top quark pair production with additional $b$-quarks in the final state are also presented. Differential cross sections are measured and are given as functions of various kinematic observables, including the transverse momentum and rapidity of the (anti)top quark and the top-antitop system and the jets and leptons of the event final state. Multiplicity and kinematic distributions of the jets produced in addition to the top pair are also investigated. The results are combined and confronted with precise theory calculations.
We also present result on top quark event modeling. State-of-the-art theoretical predictions accurate to next-to-leading order QCD interfaced with Pythia8 and Herwig++ event generators are tested by comparing the unfolded $t\bar{t}$ differential data collected with the CMS detector at 8 TeV. These predictions are also compared with the underlying event activity distributions in $t\bar{t}$ events using CMS proton-proton data collected in 2015 at a center of mass energy of 13 TeV.
I will discuss the impact of EW corrections on differential distributions in top-quark pair production at the LHC and future hadron colliders, focusing on the effects of initial-state photons. Performing a calculation at NLO in QCD+EW accuracy, the impact of photon-initiated channels is investigated in detail, on central values as well as PDF and scale uncertainties at order $\alpha_s\alpha$ and $\alpha^2_s\alpha$. A thorough comparison of results, obtained with the NNPDF2.3QED and CT14QED PDF sets, is performed at 8, 13 and 100 TeV. At 8 TeV there is a further comparison with data from differential measurements performed by ATLAS and CMS. The aforementioned content is based on arXiv:1606.01915 [hep-ph]. Specifically for 13 TeV, new results will be presented at NNLO QCD + NLO EW accuracy using the newest available PDF sets including the photon i.e. the NNPDF3.0QED and the LUXqed PDF sets. This part is based on an ongoing project.
Differential distributions for top-quark pair production can be employed to extract the top-quark pole mass. In addition to precision measurements of these distributions, accurate predictions of the observables for different values of the masses are needed. Using next-to-next-to-leading order predictions a first extraction has been performed using data taken at the Tevatron. In this talk, I will compare this method to other mass extraction methods and show that it can be a powerful tool to extract the top-quark pole mass at the LHC as well.
A phenomenological study of the final combined HERA data on inclusive
deep inelastic scattering (DIS) has been performed. The data are
presented and investigated for a kinematic range extending from
values of the four-momentum transfer of the exchanged boson, $Q^2$,
above $10^4$ GeV$^2$ down to the lowest values observable at HERA of
$Q^2$, and Bjorken $x_{\rm Bj}$ of $Q^2 = 0.045$ GeV$^2$ and
$x_{\rm Bj} = 6 \times 10^{-7}$. The data are well described by fits
based on perturbative quantum chromodynamics (QCD) using collinear
factorisation and evolution of the parton densities encompassed in
the DGLAP formalism down to $Q^2$ of a few GeV$^2$. As $Q^2$
approaches zero, the Regge formalism can describe the data. It is
shown to be appropriate up to $Q^2 \approx 0.5$ GeV$^2$. The data
covering the region between the Regge and the perturbative QCD
regimes are of particular interest. Their features are presented.
The sensitivity of CMS measurements to Parton Distribution Functions, strong coupling constant and treatment of heavy flavours in QCD analyses is presented. CMS data collected at various center-of-mass energies and their impact on the PDFs are presented. Measurements of cross sections of jet and to-quark pair production are in particular sensitive to the gluon distribution in the proton and the strong coupling, while the electroweak boson production - inclusive or associated with charm or beauty quarks give insight into the flavour separation of the proton sea and give hints to the treatment of heavy quarks in PDF-related studies.
Over the past several years, parton distribution functions (PDFs) have become more precise. However there are still kinematic regions where more data are needed to help constrain global PDF extractions, such as the sea quark distributions $\bar{d}$/$\bar{u}$ near the valence region (Bjorken-x $\approx$ 0.1 - 0.3). Current measurements appear to suggest different high-x behaviors of these distributions. The charged W cross section ratio (W$^+$/W$^-$) is sensitive to the unpolarized $u,\;d,\;\bar{u},$ and $\bar{d}$ quark distributions at large $Q^2$ set by the $W$ mass and could help shed light on this discrepancy. The STAR experiment at RHIC is well equipped to measure the leptonic decays of W bosons, in the mid-rapidity range $\left(|\eta| \leq 1 \right)$, produced in proton+proton collisions at $\sqrt{s}$ = 500/510 GeV. At these kinematics STAR is sensitive to quark distributions near Bjorken-x of 0.16. STAR can also measure the W cross section ratio in a more forward bin ranging from 1.1 $< \eta <$ 2.0, which extends the sea quark sensitivity to higher x. RHIC runs from 2011 through 2013 have collected about 350 pb$^{-1}$ of integrated luminosity, and a 2017 run is expected to provide an additional 400 pb$^{-1}$. Presented here are preliminary results for the 2011-2012 W charged cross section ratios ($\sim$100pb$^{-1}$) and an update on the 2013 charged W cross section analysis ($\sim$250 pb$^{-1}$).
Precision measurements of the Drell-Yan production of W and Z bosons at the LHC provide a benchmark of our understanding of perturbative QCD and electroweak processes and probe the proton structure in a unique way.
The ATLAS collaboration performed a precision Z/gamma* measurement at a center of mass energy of 8 TeV in the di-lepton mass range up to the TeV scale. These are performed double-differentially in dilepton mass and rapidity or dilepton mass and rapidity separation. The measurements are compared to state-of-the-art theory calculations and are found to bring strong constraints on the high x partons and the poorly constrained photon content of the proton.
Z cross sections are also measured at a center-of-mass energies of 8TeV and 13TeV, and cross-section ratios to the top-quark pair production have been derived. This ratio measurement leads to a cancellation of several systematic effects and allows therefore for a high precision comparison to the theory predictions.
The large equivalent-photon fluxes accompanying Pb ion beams at the LHC initiate photon-photon and photo-nuclear interactions which dominate when the colliding nuclei have large impact parameter (ultra-peripheral collisions). These electromagnetically-induced processes are sensitive to the nuclear wave-function and in particular the nuclear modifications of the nucleon parton distribution functions (nPDFs). As such, they are complementary to the ongoing p+A program at RHIC and the LHC, as well as the upcoming electron-ion collider (EIC) program in the US. The absolute rates of single and multiple neutron emission into one or both zero-degree calorimeters (ZDCs) will be presented, to test theoretical predictions for the photon fluxes as well as the photonuclear absorption. High-mass dilepton pair continuum rates have been measured and compared with theoretical predictions to test expectations for two-photon interactions, and good agreement with model calculations is obtained. Finally, evidence for the elastic scattering of photons γγ→γγ (“light-by-light” scattering) will be presented, a previously unobserved process made possible by the high photon flux and low event pileup provided by the LHC. While of intrinsic interest as a heretofore-unobserved standard model process, it has also been proposed as a clean channel for searches for beyond the standard model (BSM) physics.
We will report on new results concerning exclusive dilepton and diphoton production with the CMS-TOTEM Precision Proton Spectrometer (CT-PPS). For the first time, exclusive dileptons at high masses have been observed in the CMS detector while at least one or the two intact protons are measured in CT-PPS using about 10 fb-1 of data accumulated in 2016. These first results show a good understanding, calibration and alignment of the new CT-PPS detectors installed in 2016. In addition, preliminary results and expectations will be discussed concerning the search for high mass exclusive diphoton production.
We report the measurements of exclusive production of dihadrons, the Upsilon meson and WW pairs in proton-proton and ultra-peripherial proton-lead collisions at the LHC. The data are compared to results from other experiments and to theoretical predictions.
The cross-section for central exclusive production of J/psi and Psi(2S) mesons at 13 TeV is measured using the LHCb detector. Proton dissociative backgrounds are significant reduced compared to previous measurements through the use of forward shower counters, recently installed for Run 2. Plans for future measurements are also presented to exploit the new Run2 dataset.
Detailed measurements of the properties of the 125 GeV Higgs boson are fundamental for the understanding of the electroweak symmetry breaking mechanism. Measurements of the Higgs boson in the diboson final states allow to study the gauge and loop induced couplings of the Higgs boson both in production and decay modes. This talk summarizes ATLAS measurements of the 125 GeV Higgs boson in decays involving W, Z or photons.
Detailed measurements of the properties of the 125 GeV Higgs boson are fundamental for the understanding of the electroweak symmetry breaking mechanism. Measurements of the Higgs boson in fermion final states allow to study the Yukawa couplings of the Higgs boson through the decay mode and the gauge couplings of the Higgs boson through the production mode. This talk summarizes ATLAS measurements of the 125 GeV Higgs boson in decays involving b, tau and mu.
Latest results of SM Higgs measurements in the fermionic final state are presented, as well as results of searches for BSM Higgs bosons using the CMS detector at LHC. Results are based on pp collision data collected at centre-of-mass energies of 8 and 13 TeV. Results have been interpreted according to different extensions of the Standard Model, such as 2HDM, MSSM, NMSSM. These searches look for evidence of other scalar or pseudoscalar bosons, in addition to the observed SM-like 126 GeV Higgs boson, and set exclusion limits in fermionic final states and benchmark models explored. This talk reviews briefly all the major results obtained by CMS during Run I, and present the most recent searches during Run II.
Higgs boson and double Higgs boson productions suffer from large higher order corrections. This is true also when they are accompanied by further jets. The most precise results rely on computations in an effective theory where the heavy quark loops, mediating the coupling between the Higgs boson and the gluons, are integrated out. As the LHC is delivering more and more precise data, it is important to understand in detail the validity range of such effective theory predictions, in particular in view of boosted analyses. In this talk I will present detailed comparisons between effective theory results and predictions obtained in the full theory.
A first determination of the strong coupling $\alpha_s$ in
next-to-next-to leading order (NNLO) from inclusive jet and dijet
production in deep-inelastic scattering at HERA is presented.
The strong coupling is determined in a fit of jet data collected by the H1
experiment in the range of momentum transfer $5.5 < Q^2< 15000$ GeV${}^2$
and jet transverse momenta $p_T>5$ GeV. The running of the strong
coupling is probed in a single experiment over one order of
magnitude in the remornalisation scale $\mu_r$. NNLO predictions were
obtained using the program NNLOJET, where the corresponding
calculations are based on antenna subtraction techniques.
According to recent measurements, the mass of jets created in LHC energy pp collisions has broad fluctuation. Typically, the mean mass of a jet with transverse momentum 200-600 GeV/c is around 40-100 GeV/c^2, so the ratio (jet mass)/(jet energy) is of order 0.2. As this value is not negligibly small, as required for factorisation to be applicable, the virtualitis of partons created in the hard process (most probably) should not be neglected. Besides, the fragmentation of these off-shell partons has to be handled.
Based on recent works [1-4], I present a simple statistical fragmentation model, which is suitable for the treatment of the hadronisation of virtual partons as well as the inclusion of jet mass fluctuations. I present fits to fragmentation functions measured in ep and pp collisions and give prediction for the jet mass dependence of hadron multiplicity distributions inside jets.
[1] arXiv:1606.03208
[2] PoS DIS2016 (2016) 054, arXiv:1605.06876
[3] Phys. Lett. B, 718 (2012) 125-129, arXiv:1204.1508
[4] Phys. Lett. B, 701 (2011) 111-116, arXiv:1101.3023
The pion electromagnetic form factor, $F_\pi$, is a fundamentally important topic for our understanding of the hadron structure and the transition from perturbative to nonperturbative QCD. JLAB’s experiment E12-06-101 proposes to extend the high quality $F_\pi$ data to $Q^2=6.0$ GeV$^2$ as a part of JLAB’s $12$ GeV upgrade. Being motivated by this, we present a lattice QCD calculation of $F_\pi$ using the method of distillation and the variational approach which significantly reduce the excited state contamination. We study the shape of the vector form factor in the $Q^2$ range from zero to a few GeV$^2$ using Wilson quark formalism on our $203 \times 128$ anisotropic lattice configuration with light (up/down) and strange quarks in the sea and $400$ MeV pion mass.
The nucleon form factors have been evaluated in light of the improved precision of the experimental measurements and enormous theoretical progress to understand the dynamical behavior of nucleons emerging from the theory of strong interactions between quarks. We have analysed the vector and axial-vector nucleon form factors ($G^{p,n}_{E,M}(Q^2)$ and $G^{p,n}_{A}(Q^2)$) using the spin observables in the chiral constituent quark model ($\chi$CQM) which has made a significant contribution to the unraveling of the internal structure of the nucleon in the nonperturbative regime. A comprehensive analysis of the flavor decomposition of the form factors ($G^{q}_{E}(Q^2)$, $G^{q}_{M}(Q^2)$ and $G^{q}_{A}(Q^2)$for $q=u,d,s$) has also been presented. The $Q^2$ dependence of the vector and axial-vector form factors of the nucleon has been studied using the conventional dipole form of parametrization.
The results are in agreement with the available experimental data.
The study of the single-hadron semi-inclusive deep inelastic scattering process (SIDIS) is a rapidly developing and expanding area of inquiry in hadronic
physics, owing to the prospect of realizing a precision three-dimensional imaging
of the quark structure of the nucleon in momentum space. Measurements of the
azimuthal angular distributions of hadrons produced at large values of z = Eh=?
and "small" transverse momentum pT ~ \Lambda_?QCD in deep inelastic lepton-nucleon
scattering provides access to novel features of nucleon structure that are inaccessible in traditional inclusive DIS, including the e?ects of initial-state quark transverse momentum, transverse polarization of the parent nucleon and the
struck quark, and "flavor tagging" due to the varying sensitivity of di?erent
hadron species to di?fferent quark flavors. The Continuous Electron Beam Accelerator Facility (CEBAF) at Je?erson Lab has recently completed an upgrade to
a maximum beam energy of 11 GeV at ?ve passes for electron scattering experiments. The energy upgrade of CEBAF, combined with its already unrivaled intensity, duty cycle and polarization, facilitates a three-dimensional nucleon imaging program of unprecedented precision in the valence region. In this talk,I will present a brief overview of the planned CEBAF SIDIS program in experimental Halls A, B and C.
Solenoidal Large Intensity Device (SoLID) was proposed at JLab to take the full advantage of the 12-GeV upgrade. SoLID is designed to handle high luminosities with large acceptance, which is ideal for measuring transverse momentum depended parton distribution functions (TMDs). Currently there is a highly-rated approved program focusing on the study of TMDs using semi-inclusive deep inelastic scattering (SIDIS) with longitudinal/transversely polarized 3He target and a transversely polarized proton target. These experiments will provide a comprehensive set of data on proton and neutron (effective) in a wide range of kinematics, allowing us to perform precise 4-d (x, Q^2, P_T, z) mapping of leading-twist TMDs related spin asymmetries. The future SoLID data will allow for a precise extraction of nucleon tensor charge, and important TMDs such as Sivers, pretzelosity and worm-gear functions in the valence quark region. In this talk we will present the impact of future SoLID data on the extraction of tensor charge and Sivers function of u and d-quarks.
Semi-inclusive deep inelastic scattering (SIDIS) has proved to be an important tool for unveiling the inner structure of the core of the atom, the nucleons and their basic constituents. Azimuthal spin asymmetries in polarized SIDIS are directly related to transverse momentum dependent parton distributions (TMDs) and fragmentation functions. The TMDs allow one to probe the 3D dynamical structure of partons inside the nucleon. Understanding the nature of the SIDIS process is essential for TMD studies, in particular at modest energies where deviations from the leading-order factorized picture may be a significant. Precise maps of the meson cross sections and their ratios at low transverse momentum and Jefferson Lab beam energies provide a stringent test of the use of the standard SIDIS framework in terms of factorized parton distributions convoluted with fragmentation functions. The magnetic spectrometers in Hall C at Jefferson Lab are well suited for such precision measurements of fully L/T separated cross sections and their ratios. The addition of neutral particle detection enables additional opportunities. Plans for upcoming experiments that will investigate the SIDIS process at the 12 GeV Jefferson Lab will be presented.
The COMPASS legacy on the measurements of $g_1$ for proton and deuteron
through inclusive spin-dependent inelastic polarised-muon scattering
on longitudinally polarised NH$_3$ and $^6$LiD targets will be presented.
Results cover both deep-inelastic ($Q^2 > $ 1 (GeV/$c$)$^2$)
and non-perturbative ($Q^2 < $ 1 (GeV/$c$)$^2$) regions and a wide interval
in the Bjorken scaling variable. In the deep-inelastic set of data
the double-spin asymmetries and
spin-dependent structure functions are studied
in bins of $x$ and $Q^2$. Using those results an update of
the Bjorken sum rule is made and the QCD fit to the $g_1$
world data at the next-to-leading order
is performed.
In the nonperturbative region, studies of the spin asymmetry and
spin-dependent structure function for the proton are performed on four
2-dimensional grids of kinematic variables: $(x,Q^2), (\nu,Q^2), (x,\nu)$
and $(Q^2,x)$. The asymmetry and the structure function are found to be
positive in the whole range of $x$, $4\cdot 10^{-5} < x < 4\cdot 10^{-2}$,
for the first time displaying spin effects at such low values of $x$.
A new combined analysis of spin-averaged and spin-dependent PDFs reveals for the first time the x dependence of helicity PDFs in the x ~ 1 region, free from assumptions about the behavior of unpolarized PDFs that have been inherent in all previous global QCD analyses of spin data.
We present the recent progress on parton distribution functions (PDF) of the proton from the CTEQ-TEA collaboration.
I present a summary of the current status of MMHT PDFs. Recent updates include the effects of additional data from the LHC. The inclusion of new jet data and of the full NNLO corrections to the cross sections are studied. We also look at the implications from improved data on vector boson production and how these affect the quark flavour decomposition. Another focus is the inclusion of QED corrections and the photon PDF.
The exploitation of the exciting physics program of the Run II of the Large Hadron Collider requires high-precision theoretical calculations, of which the parton distribution functions (PDFs) of the proton are a central ingredient. In this talk we present the new update of the NNPDF family of global analysis, NNPDF3.1. This new PDF set is based on the NNPDF3.0 fitting framework supplemented with a wide variety of new experimental measurements from HERA, Tevatron and the LHC. The list of new datasets includes top-quark pair differential distributions from ATLAS and CMS, the transverse momentum distributions of the Z boson from ATLAS and CMS, the D0 electron and muon W asymmetries from the complete Tevatron dataset, the legacy Run I LHCb measurements of W and Z production in the forward region, and the ATLAS W,Z 2011 inclusive measurements, in addition to several others. Fits both with perturbative charm and with a fitted charm PDF are presented, which are then used for precision studies about the charm content of the proton. We briefly discuss the phenomenological implications of NNPDF3.1 for LHC phenomenology at Run II.
We present results from the most recent global QCD analysis by the CTEQ-Jefferson Lab (CJ) Collaboration on the flavour content of the nucleon sea quark distributions. Constraints from LHC, Fermilab and Jefferson Lab data on the SU(2) flavour asymmetry, dbar - ubar, as well as on the strange asymmetry s - sbar will be discussed.
The APPLgrid and fastNLO projects provide a fast and flexible way to reproduce the results of perturbative QCD cross section calculations with any input PDF. The latest developments from these projects are presented, concentrating especially on the joint project (APPLfast), providing a common interface to state-of-the-art NNLO QCD calculations from NNLOJET. Additional features from new develoments in the Spectrum tool - a web utility allowing comparison of data with theory calculations - are also discussed.
The electromagnetic field of a fast moving lead ion at the LHC is an intense source of quasi-real photons. This makes it possible to study J/Psi exclusive photoproduction off protons in p-Pb collisions at the LHC. This process is sensitive to the gluon content of the target.
Using Run1 data, ALICE has measured the exclusive J/Psi photoproduction cross section for centre-of-mass energies of the photon-proton system ranging from 20 GeV to 700 GeV. Furthermore ALICE has collected new data in Run2 reaching even larger energies. In this talk, the latest available results will be given.
The intense photon fluxes of relativistic nuclei provide a possibility
to study photonuclear and two-photon interactions in ultra-peripheral collisions (UPC) where the nuclei do not overlap and no strong nuclear interactions occur.
Within the Vector-meson Dominance Model (VDM), the rho0 contribution prevails in the QCD photon structure function and the gamma+A -> rho0+A process in heavy-ion UPC is a tool to test the, so-called, black disk regime where the target nuclei appears like a black disk and the total rho0+A cross section reaches its limit. RHIC and first LHC results have deviated from some Glauber+VDM calculations, which thus call for new data.
ALICE reports measurements on rho0 photoproduction cross sections
in Pb-Pb UPC with data taken at sqrt(s_NN)=2.76 TeV and new measurements with the data taken at sqrt(s_NN)=5.02 TeV. The mid-rapidity cross section of coherent rho0 photoproduction is measured,and it is compared to theoretical models.
The TOTEM collaboration at the LHC has completed its analysis of the elastic, inelastic and total proton-proton cross-sections (via the optical theorem) at sqrt(s) = 2.74 TeV. The new measurement lies close in energy to the Tevatron's 1.8 TeV with its two slightly conflicting total cross-section results.
The presentation will put the new measurement in the context of completed, ongoing and future measurements at other energies.
The aim of the ATLAS Forward Proton (AFP) detector system is the measurement of protons scattered diffractively or electromagnetically at very small angles. The first arm of the system was installed last year and AFP took data in several commissioning and physics runs. The installation of the second arm is ongoing and will be completed in time for the 2017 data taking period. This will allow measurements of processes with two forward protons: central diffraction, exclusive production, and two-photon processes. During the presentation, the early results and experience from the first year of data taking will be presented together with the status of the second-arm installation and plans for the future.
The photoproduction of isolated photons is measured using diffractive events
recorded by the ZEUS detector at HERA. Cross sections are evaluated in the
photon transverse-energy and pseudorapidity ranges $5 < E_T^{\gamma} < 15$ GeV
and $-0.7 < \eta^{\gamma} < 0.9$, inclusively and with a jet with
transverse-energy and pseudorapidity in the ranges $4 < E_T^{\rm jet} < 35$ GeV
and $-1.5 < \eta^{\rm jet} < 1.8$, for an integrated electron-proton luminosity
of 374 ${\rm pb}^{-1}$. A number of kinematic variables are studied and compared
to predictions from the RAPGAP Monte Carlo model. In considering the fraction of
the energy of the colourless (``Pomeron'') exchange that is transferred to the
photon--jet final state, $z_P$, it is found that the data lie above the RAPGAP
predictions for $z_P > 0.9$, giving evidence for direct-Pomeron interactions. The
shapes of the kinematic distributions of events below and above this value of
$z_P$ are separately well described by RAPGAP. This and other features provide
evidence for a universal set of parton distribution functions in the Pomeron.
The associated production of the Higgs boson with top quarks should allow the direct observation of the coupling of the Higgs boson to top quarks. The channel also benefits from a large cross-section increase between 8 and 13 TeV. ATLAS results for the search of the 125 GeV Higgs boson in the ttH production mode will be presented.
The latest results of searches for the Standard Model Higgs boson produced in association with a top quark-antiquark pair (ttH), or with a single top quark (tHq) are presented. The analyses have been performed using the 13 TeV pp collisions data recorded by the CMS experiment in 2015 and 2016. The results are presented in the form of the best fit to the signal strength measured with respect to the Standard Model prediction and its expected and observed 95% C.L. upper limits.
Theoretical uncertainties in the simulation of $t\bar{t}b\bar{b}$ production represent one of the main obstacles that still hamper the observation of Higgs-boson production in association with top-quark pairs in the $H \to b\bar{b}$. We present a next-to-leading order (NLO) simulation of $t\bar{t}b\bar{b}$ production with massive b-quarks matched to the Pythia within the POWHEG method with the hope of reconciling tension between previous calculations based on the MC@NLO method.
In this talk the latest results for soft gluon resummation at fixed invariant mass for $pp \to t\bar{t}H$ will be presented. The resummation is extended beyond next-to leading logarithmic accuracy. The invariant mass resummation results will be presented in the form of the inclusive cross section and the invariant mass distribution, including scale uncertainty.
Studying the pair production of Higgs bosons at the LHC is important as it is sensitive to the Higgs trilinear coupling. It therefore allows for a direct test of the Higgs potential and the mechanism of electroweak symmetry breaking.
Since the heavy top limit provides only a poor description of Higgs boson pair production, a precise theoretical description of this process requires the evaluation of massive top loops at leading order, and massive two-loop diagrams at NLO. In this talk we will present a calculation of the NLO cross section for Higgs boson pairs, retaining the full dependence on the top-quark mass, and supplementing it with a parton shower. We further investigate the finite top-quark mass effects and the impact of the parton shower on several differential observables.
The production of pairs of Higgs bosons at hadron colliders provides unique information on the Higgs sector and on the mechanism underlying electroweak symmetry breaking (EWSB). Most studies have concentrated on the gluon fusion production mode which has the largest cross section. However, despite its small production rate, the vector-boson fusion channel can also be relevant since even small modifications of the Higgs couplings to vector bosons induce a striking increase of the cross section as a function of the invariant mass of the Higgs boson pair. In this work, we exploit this unique signature to propose a strategy to extract the hhVV quartic coupling and provide model-independent constraints on theories where EWSB is driven by new strong interactions. We take advantage of the higher signal yield of the 4b final state and make extensive use of jet substructure techniques to reconstruct signal events with a boosted topology, characteristic of large partonic energies, where each Higgs boson decays to a single collimated jet . Our results demonstrate that the hhVV coupling can be measured with up to 20% precision at the LHC, while a 1% precision can be achieved at a 100 TeV collider.
Threshold resummation is often used to improve the theoretical accuracy of inclusive cross sections at hadron colliders. However, when differential distributions are considered, we acquire sensitivity to more energy scales which triggers the appearance of different types of logarithms. In these situations a joint resummation formalism becomes relevant. The general framework for joint threshold and $q_T$ resummation has existed for some time, but has only ever been applied at NLL accuracy. In this presentation we discuss an extension of the method for joint resummation to NNLL accuracy and apply it to Z-boson production at Tevatron and LHC as well as the heavier Z' production at LHC.
The production of vector bosons (W, Z, gamma) in association with jets is a stringent test of perturbative QCD and is a background process in searches for new physics. Total and differential cross-section measurements of vector bosons produced in association with jets and heavy flavour quarks in proton-proton collisions performed by the CMS collaboration at the LHC are presented. The measurements are compared to the predictions of event generators and theoretical calculations.
I will be discussing the production of a single Z or W boson in association with jets at the LHC. I will be presenting results obtained by matching NLO QCD predictions with the Herwig 7 and Pythia 8 parton showers, and by merging all of the underlying matrix elements with up to two light partons at the Born level. These will be compared to several measurements by the ATLAS and CMS collaborations.
A detailed comparison between four- and five- flavour scheme predictions for $b$-associated production for $Z$ and Higgs bosons is presented. Results obtained for $Z$ production at 7 TeV are then compared to LHC data. The comparison is then used
to validate results for $b$-associated Higgs boson production at the 13 TeV Run II.
The production of jets in association with vector bosons is an important process to study QCD in a multi-scale environment. The ATLAS collaboration has performed measurements of vector boson+jets cross sections, differential in several kinematic variables, in proton-proton collision data taken at center-of-mass energies of 8TeV and 13TeV. The measurements are compared to state-of-the art theory predictions and can be used to constrain the gluon PDF.
In data collected at 8TeV, the collaboration has measured the production of W boson+jets with a large transverse momentum of the leading jet, which enriches the collinear production of the gauge boson and a jet. The measurements are compared to state-of-the-art QCD calculations and Monte Carlo simulations.
Latest tests of double parton scattering, underlying event tunes, minimum bias, and diffraction made by comparing CMS Run I and Run II data to the state-of-the-art theoretical predictions interfaced with up-to-date parton shower codes are presented. Studies to derive and to test the new CMS event tune obtained through jet kinematics in top quark pair events and global event variables are described.
This talk focuses on the impact of top-quark spin polarization effects in Higgs boson production in association with a top-quark pair, where the Higgs boson decays to two photons. Predictions for the signal are compared with direct top-quark pair production in association with two photons at NLO+PS.
Precise measurements of the properties of the top quark test the Standard Model (SM) and can be used to constrain new physics models. As it may be significantly enhanced by the presence of new physics, the ttbar production charge asymmetry is measured inclusively and differentially using the 8 TeV ATLAS dataset using both the lepton+jets and dilepton channels, including a dedicated measurement for highly boosted top-quarks. The top-quark is predicted in the SM to decay almost exclusively into a $W$ boson and a $b$-quark. We present a wide range of searches for non-SM top quark decays using the 8 TeV and 13 TeV ATLAS datasets, including $t \to q H$, $t \to q \gamma$ and $t \to q Z$. In addition, measurements of the $W$-helicity and spin correlations in $t\bar{t}$ production are presented as well as new measurements of $CP$ asymmetries in $b$-hadron decays using top-quark events.
Measurements of several top-quark properties are presented, obtained from the CMS data collected at various centre-of-mass energies. The results include measurements of the top pair charge asymmetry, the $W$ helicity in top decays, $CP$ violation, $t\bar{t}$ spin correlation, top polarisation and the search for anomalous couplings including Flavour Changing Neutral Currents. The results are compared with predictions from the standard model as well as new physics models. The cross section of $t\bar{t}$ events produced in association with a $W$, $Z$ boson or a photon is also measured.
Measurements of single top-quark production in proton-proton collisions are presented based on the 8 TeV and 13 TeV ATLAS datasets. In the leading order process, a $W$ boson is exchanged in the $t$-channel. The cross-section for the production of single top-quarks and single anti-top-quarks total production cross sections, their ratio, as well as a measurement of the inclusive production cross section is presented. At 8 TeV, differential cross-section measurements of the $t$-channel process are also reported, these analyses include limits on anomalous contributions to the $Wtb$ vertex and measurement of the top quark polarization. A measurement of the production cross section of a single top quark in association with a $W$ boson, the second largest single-top production mode, is also presented. Finally, evidence for $s$-channel single-top production in the 8 TeV ATLAS dataset is presented. All measurements are compared to state-of-the-art theoretical calculations.
Measurements of single top quark production are presented, performed using CMS data collected in 2011, 2012 and 2015 at centre-of-mass energies of 7, 8 and 13 TeV respectively. The cross sections for the electroweak production of single top quarks in the $t$-channel and in association with $W$-bosons is measured and the results are used to place constraints on the CKM matrix element $V_{tb}$. In the $t$-channel the ratio of top and anti-top production cross sections is determined and compared with predictions from different parton density distribution functions. Measurements of top quark properties in single top quark production are also presented, such as the top-quark polarisation, the probe of $tWb$ vertex through the $W$-helicity measurement in top quark decay and the searched for anomalous couplings to gluons, photons or $Z$ bosons. A search for the $s$-channel is also performed.
The electroweak production of single top quarks offers a unique laboratory for precision tests of top-quark related parameters of the Standard Model and possible extensions thereof. To obtain a precise and accurate parameter determination efficient, unbiased and theoretically unambigous analysis methods are needed. The Matrix Element Method (MEM) has proven beneficial to make maximal use of the information available in experimental data. However, so far it has mostly been applied in Born approximation only. In this talk we discuss the extension to NLO QCD accuracy. As a prerequisite we present an efficient method to calculate event weights for jet events at NLO accuracy. As illustration and proof of concept we use the MEM@NLO to reproduce the top-quark mass from single top events generated at NLO accuracy. We observe that analysing NLO events with LO likelihoods can introduce a pronounced bias in the extracted mass which would require significant calibration with associated uncertainties.
COMPASS final results on multiplicities of charged hadrons,
pions and kaons, produced in the deep inelastic muon scattering
off an isoscalar target will be presented. Measurements were
taken in bins of x,y and z in a wide kinematic range.
The hadron and pion data show a good agreement
with (N)LO expectations and some of the
preliminary measurements have been already incorporated
in the global NLO fits to the world data.
The pion multiplicity results were used to
extract the LO quark fragmentation functions.
The most interesting are kaon multiplicities allowing to extract kaon
fragmentation functions, crucial in solving the strange quark
polarisation puzzle. The COMPASS results are quite different from the
expectations of the NLO DSS fit; nor they can be described by the LO QCD.
In this context the importance of K+/K- multiplicity ratio
at high z will be discussed.
We present an extraction of unpolarized partonic transverse momentum distributions (TMDs) from a simultaneous fit of available data measured in semi-inclusive deep inelastic scattering and in Drell-Yan processes through the production of photon and Z bosons. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy. The analysis is restricted to the low-transverse-momentum region, with no matching to fixed-order calculations at high transverse momentum. We introduce specific choices to deal with TMD evolution at low scales, of the order of 1 GeV2. This could be considered as a first attempt at a global fit of TMDs.
The transversity distribution was extracted for the first time from data on the transverse momentum distribution of single hadrons produced in semi-inclusive deep-inelastic scattering. The transversity was recently extracted also from the same process but leading to the inclusive production of hadron pairs in the final state. The latter analysis can be conveniently performed in the framework of collinear factorization where the elementary mechanism is represented as the simple product of transversity and of a suitable chiral-odd function describing the fragmentation of a transversely polarized parton into a pair of hadrons inside the same current jet. The same elementary mechanism was predicted long ago to generate an asymmetry in the azimuthal distribution of the hadron pairs when they are produced in proton-proton collisions with one transversely polarized proton. Recently, the STAR Collaboration has observed this asymmetry. We analyze the impact of these data on our knowledge of transversity.
In this talk I will discuss our work (Phys.Rev.D94(2016)034014) on an improved implementation for combining transverse-momentum-dependent (TMD) factorization in semi-inclusive DIS and collinear factorization. TMD factorization is suitable for low transverse momentum physics, while collinear factorization is suitable for high transverse momenta and for a cross section integrated over transverse momentum. The result is a modified version of the standard matching prescription traditionally used in the Collins-Soper-Sterman formalism and related approaches. We briefly discuss how our study of matching between the TMD approach and collinear factorization impacts the study of the 3-D structure of the nucleon.
I present a first determination of a set of collinear fragmentation functions of charged pions based on the NNDPF methodology. The determination includes a wide set of single-inclusive annihilation data and is performed up to next-to-next-to-leading order accuracy in perturbative quantum chromodynamics. I discuss the results of the fits, highlighting the quality of the description of the data, their stability upon the inclusion of higher-order corrections, and some of their implications in the investigation of the spin structure of the nucleon.
We present a new global QCD analysis of fragmentation functions (FF) using Monte
Carlo methods. The analysis includes all existing semi-inclusive hadron
production data from electron-positron annihilation experiments including the most
resent measurements from Belle and BaBar. Preliminary analysis of combined
FF analysis with spin dependent PDF will be shown.
APFEL is a numerical code specialised for PDF fits that provides a fast and accurate solution of the DGLAP equations. In addition to PDF evolution, APFEL also provides a module for the computation of DIS cross sections in several mass schemes. In this contribution, I will present the most recent and relevant developments carried out in APFEL. They include: the computation of the time-like evolution, the implementation of the SIA cross sections needed for the determination of FFs, the small-x resummed evolution and structure functions, and the implementation of the NLO QED corrections both to the DGLAP evolution and the DIS structure functions. I will then mention some of the most recent results obtained using APFEL and finally I will conclude discussing future plans related to the determination of FFs and TMDs.
We have developed a new procedure to determine Parton Distribution Functions (PDFs) and their uncertainties, based on Markov Chain Monte Carlo
methods. We will show in this talk how we can replace the standard $\chi^2$ minimization by procedures grounded on Statistical Methods, and on Bayesian inference in particular, thus offering additional insight into the rich field of PDFs. The formulation of PDFs
determination in terms of Bayesian inference, the Monte Carlo algorithm we have implemented in the xFitter code, and the first results
we have obtained will be presented.
The workshop on Parton Distributions and Lattice Calculations in the LHC era (PDFLattice2017) has been hosted at Balliol College, Oxford (UK), shortly before DIS2017. The workshop has brought together communities involved in the determination of the parton distribution functions (PDFs) from lattice QCD, on the one hand, and from global QCD analyses of the data, on the other hand. The goal was to set precision targets for lattice calculations so that they can contribute, together with the experimental input, to achieve a next generation of PDF determinations. This talk summarizes the relevant outcome of the workshop.
While it is long known that the quark stature of the nucleon is modified in the nuclear medium, we still lack understanding of the underlying physical mechanism that causes this modification. Understanding this mechanism will teach us about the interplay between partonic and nucleonic degrees of freedom in nuclear systems and is therefore a main challenge of modern nuclear physics.
In this talk I will overview new insight to the origin of the EMC effect, obtained from recent phenomenological and theoretical studies. Special emphasis will be given to EFT and QCD based studies, both relating the origin of the EMC effect to the existence of short-range correlated pairs of nucleons in nucleon.
Given time I will overview novel experiments that are approved to run at the upgraded Jefferson-Lab facility and are expected to shad new light on the EMC effect and its implications to the 3D structure of bound nucleons.
The new insight presented in this talk is also summarized in a recent review paper commissioned by Reviews of Modern Physics (arXiv 1611.09748).
Progress is reported with a phenomenological analysis in full view of chromodynamics of a plausible Bethe-Heitler-like approach to measurements of exclusive elastic and dissociative electroproduction cross sections for vector-meson (VM) “quarkonia” of different flavour, namely ?\rho(760), u ubar - d dbar, \phi(??1019) s sbar, J\psi?(3096) c cbar and \Upsilon(??9460) b bbar? . First results are presented in the form of acceptable fits to measurements made by the H1 and Zeus experiments at the HERA electron-proton collider of the cross sections. The Bethe-Heitler-like hypothesis includes the factorisable, flavor-dependent,
combination of quark-antiquark contributions which describe measurements of real and virtual photon structure (??F_2^{\gamma*}), together with the appropriate, and universal, Regge-asymptotic form for flavour-blind, elastic, quark-proton (?qp) scattering which is based analyticity and on measurements
of the proton structure function F_2?? at appropriate Bjørken–x. The measurements are well described with constituent masses of u, d, s, c and b quarks and flavour-blind qp? scattering for which the Regge-asymptotic expansion is truncated at one leading pole with intercept consistent with that which tradition demands is called a “pomeron” and which depends on the “length” of elastic ?scattering. The pomeron is thus seen both to be at work at a scale which is below that of the interacting proton, that is of confinement, and, provided that account is taken of the “length” of ?scattering, to be universal.
Measurements of open charm production are presented in diffractive deep inelastic scattering ($5< Q^2< 100$ GeV$^2$), based on 287 pb$^{−1}$ of H1 HERA-II data recorded at the center of mass energy sqrt(s)=319 GeV. The event topology is given by $ep\to eXY$ , where the system $X$, containing at least one $D^{∗}(2010)$ meson, is separated from a leading low-mass proton dissociative system Y by a large rapidity gap. The kinematics of $D^∗$ candidates are fully reconstructed in the $D^{∗}\to K\pi\pi$ decay channel. The measured cross sections are compared at the level of stable hadrons with next-to-leading order QCD predictions obtained in the massive scheme, where the charm quark is produced via the boson-gluon fusion. The calculations rely on the collinear factorization theorem and are based on diffractive parton densities previously obtained by H1 from fits of the inclusive diffractive cross sections. The measured data are further used to estimate the ratio of diffractive to inclusive open charm production in deep inelastic scattering.
Ultra-Peripheral Pb-Pb collisions, in which the two nuclei pass close to each other but at an impact parameter larger than the sum of their radii, provide information about the initial state of nuclei. In particular, J/Psi production in such collisions proceeds by photon-gluon interactions, and is sensitive to the nuclear gluon distribution. The ALICE collaboration has published measurements of UPC J/Psi production in LHC Run 1 at both forward and mid-rapidity, and has obtained a substantially larger data set in 2015 from LHC Run 2. The increased statistics has allowed a more precise study, and the higher collision energy means that lower values of Bjorken-x can be probed. In this study the first physics results from Run 2 on this channel will be presented.
We present a method to extract the photonuclear cross section for the coherent production of J/Psi off lead nuclei using peripheral and ultra-peripheral cross sections measured at the LHC. The method allows to extract the photonuclear cross section up to a centre-of-mass energy of around 500 GeV.(Corresponding to x-Bjorken of 4.5 10^-5.) Using the photonuclear cross section, and the impulse approximation, one can compute a nuclear suppression factor, which can then be compared to the predictions of nuclear shadowing from any model.
In particular, we compare it to a leading-twist computation. We find a large contribution of gluon shadowing at the largest energies.
We compute top-quark induced contributions to the hadronic decay of the standard model Higgs boson, to the fourth order in $\alpha_s$. We work in an effective theory in which the Higgs boson may couple directly to bottom quarks and gluons. Our results prove to be of a comparable size to the purely massless contributions available in the literature.
We study the effects of dimension six operators on the Higgs decay into
four lepton channel. The calculation of new matrix element is performed
in the Higgs basis and it is implemented in a Monte Carlo event generator.
The code also allows the calculation in other popular choices of basis for
the dimension six operators. We have considered all the relevant operators,
both the CP-even and CP-odd operators, which contribute to this decay
channel. Choosing some benchmark values for the parameters of the Higgs
basis, we compare our predictions for partial decay width and some important
kinematic distributions with the corresponding NLO(EW) SM predictions.
The impact of several dimension-six operators of the standard
model effective field theory relevant for vector-boson fusion and associated Higgs boson production at the LHC is investigated at next-to-leading order accuracy in QCD, including matching to parton showers. The importance of the subsequent reduction of the theoretical uncertainties in improving the possible discrimination between effective field theory and standard model results is shown. We demonstrate that the range of the Wilson coefficient values allowed by a global fit to LEP and LHC Run~I data can be further constrained by LHC Run~II future results.
Some theories predict Lepton Flavour Violating decays of the Higgs boson, while other predict enhanced decay rates into new light pseudoscalar bosons "a" or invisible particles. Also enhanced rates in rare decay modes like Phi-photon are considered. In this presentation the latest ATLAS results on searches for such non-standard and rare decays will be discussed.
The discovery of lepton flavour violating interactions will be striking evidence for physics beyond the Standard Model. Focusing on the three decays τ∓→μ±μ∓μ∓, τ∓→e±μ∓μ∓ and τ∓→e∓μ∓μ±, we evaluate the discovery potential of current and future high-energy colliders to probe lepton flavour violation in the τ sector. Based on this potential we determine the expected constraints on parameters of new physics in the context of the Type-II Seesaw Model, the Left-Right Symmetric Model, and the Minimal Supersymmetric Standard Model. The existing and ongoing 13 TeV run of the Large Hadron Collider has the potential to produce constraints that outperform the existing e+e− collider limits for the τ∓→μ±μ∓μ∓ decay and achieve a branching fraction limit of ≲10−8. With a future circular e+e− collider, constraints on the τ→lμμ branching fractions could reach as low as a few times 10−12.
We present angular correlations in multi-jet events at highest center-of-mass energies and compare the measurements to theoretical predictions including higher order parton radiation and coherence effects.
ATLAS measurements of angular correlations between particle pairs at large pseudorapidity separation in pp and pPb collisions are presented. The data were collected using a combination of the minimum-bias and high track-multiplicity triggers. A detailed study of the dependence of two-particle correlations on the charged particle multiplicity, transverse momentum of the pair constituents and the pseudorapidity separation between particles forming a pair is shown. Measurements of multi-particle cumulants in the azimuthal angles of produced particles in wide pseudorapidity (|η|<2.5) and multiplicity ranges, with the aim to extract a single particle anisotropy coefficient, v1-v5, are also presented. These measurements can help to understand the origin of the long-range correlations seen in high-multiplicity pp and p+Pb collisions.
The transverse momentum spectra, $d^2\sigma/(d\eta dp_T^2)$, of charged hadrons produced in various high energy interactions (pp, $\gamma$p, $\gamma \gamma$, heavy-ion collisions) and measured in different experiments from ISR to LHC are considered simultaneously within several phenomenological models. As a result, the recently introduced "two component model" is shown to provide a much better description of the available experimental data than other widely used parameterizations (eg. Tsallis or Hagedorn). Moreover, the relative contributions of the two components of this model to the spectra: the exponential ("thermal") and the power-law ("hard") - are found to vary with the type and the energy of the collisions, the type of the produced hadron, the charged multiplicity and the measured pseudorapididty region. The possible mechanism of this effect is discussed: while the thermal component is produced in the fragmentation of the color string due to the effective event horizon introduced by confinement, the power-law term resembles the Regge theory with the perturbative QCD pomeron.
The observed dependences are used to make predictions on the mean transverse momenta $< p_T >$, pseudorapidity distributions $d\sigma/d\eta$ and double-differential cross-sections $d^2\sigma/d\eta dp_T^2$ at LHC-energies, which are tested on the latest experimental data and predictions for future measurements are presented.
Photons and weak bosons do not interact strongly with the dense and hot medium formed in the nuclear collisions, thus should be sensitive to the nuclear modification of parton distribution functions (nPDFs). The in-medium modification of heavy quarkonium states plays an important role in studying the hot and dense medium formed in the larger collision systems. The ATLAS detector, optimized for searching new physics in proton-proton collisions, is especially well equipped to measure photons, Z, W bosons and quakonium in the high occupancy environment produced in heavy-ion collisions. We will present recent results on the prompt photon, Z, W boson and quarkonia yields as a function of centrality, transverse momentum and rapidity, from the ATLAS experiment.
I discuss the interpretation of the top-quark mass measurements, which rely on the use of Monte Carlo parton showers, in terms of theoretical definitions, such as the pole mass. I also debate the role played by non-perturbative effects, namely colour reconnection and bottom-quark hadronization, in the top-mass determination and present preliminary results, based on the simulation of fictitious top-flavoured hadrons, which may help to shed light on the theoretical uncertainty.
Measurements of the top quark mass are presented, obtained from CMS data collected in proton proton collisions at the LHC at centre-of-mass energies of 7 TeV and 8 TeV. The mass of the top quark is measured using several methods and channels, including the reconstructed invariant mass distribution of the top quark, an analysis of endpoint spectra as well as measurements from shapes of top quark decay distributions. The dependence of the mass measurement on the kinematic phase space is investigated. The results of the various channels are combined and compared to the world average. The top mass and also $\alpha_{s}$ are extracted from the top pair cross section measured at CMS.
The latest measurements of the top quark mass using the ATLAS experiment are presented. A measurement based on a multi-dimensional template fit that can constrain the uncertainties on the energy measurements of jets is presented and combined with a measurement using dilepton events. A measurement in the all-hadronic channel is also reported. In addition an analysis of the top quark mass using leptonic kinematic variables is discussed. The measurement uses a novel technique to measure the top quark mass with minimal dependence on hadronic jets. Measurements that use precision theoretical QCD calculations for both inclusive ttbar production and ttbar production with an additional jet are also presented to extract the top quark mass in the pole-mass scheme.
We present a method to establish experimentally the relation between the top-quark mass $m_t^{MC}$ as implemented in Monte-Carlo generators and the Lagrangian mass parameter $m_t$ in a theoretically well-defined renormalization scheme. We propose a simultaneous fit of $m_t^{MC}$ and an observable sensitive to $m_t$, which does not rely on any prior assumptions about the relation between $m_t$ and $m_t^{MC}$. On the one hand, this offers the advantage that the measured observable is independent of $m_t^{MC}$, thereby improving its physics interpretation. On the other hand it can be used subsequently for a determination of $m_t$. The analysis strategy is illustrated with examples for the extraction of $m_t$ from inclusive and differential cross sections for hadro-production of top-quarks.
The proton-lead programme at CERN's Large Hadron Collider allowed the study of cold-nuclear matter effects from the initial state, such as Cronin enhancement, nuclear shadowing and gluon saturation. They result in a modification of the production cross section and thus provide crucial tests of predictions from perturbative Quantum-Chromodynamics. Furthermore, these control measurements are needed to characterise the extent to which initial-state effects can be differentiated from effects due to final-state interactions in the so-called quark-gluon plasma, produced in high-energy collisions of heavy atomic nuclei.
In this contribution, recent results on the measurements of light-flavour production and jets will be presented. Especially the multi-strange baryon yields allow the study of the canonical suppression in small systems, whereas jets have been studied in term of the acoplanarity between full and charged jets and the nuclear modification factor as a function of collision centrality. The impact of these measurements in terms of modifications of the PDFs in nuclear matter will be discussed and compared with models.
Nuclear parton distribution functions are essential to the understanding of proton-lead collisions. We will review several measurements from CMS that are particularly sensitive to nPDFs. W and Z bosons are medium-blind probes of the initial state of the collisions, and we will present the measurements of their production cross sections in pPb collisions at 5.02 TeV, and as well a asymmetries with an increased sensitivity to nPDFs. We will also report measurements of charmonium production, including the nuclear modification factor of J/psi and psi(2S) in pPb collisions at 5.02 TeV, though other cold nuclear matter effects may also be at play in those processes. At last, we will present measurements of the pseudo-rapidity of dijets in pPb collisions at 5.02 TeV.
We have studied the prospects of using the Drell–Yan dilepton process in pion–nucleus collisions as a novel input in the global analysis of nuclear parton distribution functions (nPDFs). In a NLO QCD framework, we find the measured nuclear cross-section ratios from the NA3, NA10 and E615 experiments to be largely insensitive to the pion parton distributions and also compatible with the EPS09 and nCTEQ15 nPDFs. These data sets can thus be included in global nPDF analyses without introducing significant new theoretical uncertainties or tension with the other data. In particular, we explore the constraining power of these data sets on the possible flavour asymmetry in the valence-quark nuclear modifications. Moreover, using the COMPASS kinematics we present predictions for pion charge difference ratio, a new measurable which could help further constrain this asymmetry.
We report on EPPS16 - the first analysis of NLO nuclear PDFs where LHC p-Pb data (Z, W, dijets) have been directly used as a constraint. In comparison to our previous fit EPS09, also data from neutrino-nucleus deeply-inelastic scattering and pion-nucleus Drell-Yan process are now included. Much of the theory framework has also been updated from EPS09, including a consistent treatment of heavy quarks in deeply-inelastic scattering. However, the most notable change is that we no longer assume flavour-blind nuclear modifications for valence and sea quarks. This significantly reduces the theoretical bias. All the analysed data are well reproduced and the analysis thereby supports the validity of collinear factorization in high-energy collisions involving heavy nuclei. However, flavour by flavour, the uncertainties are still rather large.
We use nCTEQ15 nPDFs with uncertainties to identify measurements which
have a potential impact on nuclear corrections and flavor
differentiation. In particular, recent LHC W/Z vector boson
production data in proton-lead and lead-lead collisions are quite
sensitive to heavier flavors (especially the strange PDF). This
complements the information from neutrino-DIS data. As the proton
flavor determination is dependent on nuclear corrections (from heavy
target DIS, for example), this information may also help improve
proton PDFs.
We present the status of our calculation of nuclear parton distribution functions on the basis of our microscopic model, which takes into account a number of nuclear effects including nuclear shadowing, Fermi motion and nuclear binding, nuclear meson-exchange currents and off-shell corrections to bound nucleon distributions. We discuss a number of applications from Deep Inelastic Scattering to the Drell-Yan production. In particular, we present our results for the nuclear corrections in the deuteron and the corresponding constraints on the d/u ratio from global QCD fits, as well as for the rapidity distributions of W and Z boson production in p+Pb collisions at the LHC [PRD 94 (2016) 113013].
We investigate the energy dependence of the photo-production cross-section of vector mesons J/Psi and Upsilon on protons. In particular we are interested in the question whether the energy dependence has a description in terms of perturbative low x (i.e. BFKL) evolution or whether a successful description requires to invoke effects related to gluon saturation. To answer this question we study at first exclusive J/Psi and Upsilon production cross-sections and find that (collinear improved) NLO BFKL can provide a very good description of both HERA and LHC data. We will provide a detailed discussion of our result and point out potential observables which might allow to distinguish between low x evolution with and without saturation effects in photo-production processes at the LHC.
We have developed a model in which we treat photoproduction of charmonia via the color dipole approach taking into account the quantum fluctuations of the proton structure. These fluctuations are characterized by hot spots, randomly generated in the transverse plane, whose number grows with decreasing Bjorken-$x$. Our model successfully reproduces the $F_2(x,Q^2)$ data from HERA at the relevant scale, as well as the exclusive and dissociative $J/\Psi$ photoproduction data from H1 and ALICE. Our model predicts that once the proton is fully populated by hot spots the dissociative $J/\Psi$ cross section reaches a maximum and then decreases steeply with energy. Our prediction provides a clear signature for gluon saturation at LHC energies.
One of the striking results of the LHC has been the observation of collective behavior in high-multiplicity proton-proton and proton-nucleus collisions. These signals are similar to those that have been previously seen in collisions of heavy nuclei, and have been interpreted as a result of the hydrodynamic evolution of the produced QCD matter.
Initial state geometry is a necessary input to hydrodynamical simulations. The knowledge of the proton density profile, and its event-by-event fluctuations, is then crucial for properly interpreting the experimental pA and pp results.
We discuss how exclusive vector meson production measured at HERA can be used to constrain proton shape and the shape fluctuations. In particular, we show that incoherent diffractive vector meson production data suggest that there are large eventy-by-event fluctuations in the proton shape. This information is then applied to proton-nucleus collisions, where we show that with hydrodynamical simulations it is possible to obtain a good description of the flow harmonics measured in high multiplicity proton-nucleus collisions.
Ultraperipheral pA collisions at the LHC, being dominantly photon-proton scatterings, provide access to the exclusive vector meson production at much higher energies than what was accessible at HERA. This makes it possible to study the Bjorken-x evolution of the geometric shape of the proton. The x evolution can be calculated by solving the small-x JIMWLK evolution equation. We present results for diffractive cross sections at the LHC energies and discuss how the ultraperipheral pA collisions can constrain the proton shape at very small x.
References:
H. M, B. Schenke, Phys. Rev. D94, 2016, 034042, arXiv:1607.01711
H.M, B. Schenke, Phys. Rev. Lett. 117, 2016, arXiv:1603.04349
H. M., B. Schenke, C. Shen, P. Tribedy, in preparation
H. M., B. Schenke, in preparation
We present the first calculations for dijet production in diffractive deep-inelastic scattering (DIS) at next-to-next-to-leading order accuracy (NNLO). The calculations are based on the antenna subtraction formalism, where the hard coefficients are convoluted with available PDFs for diffractive scattering (DPDFs). Unfortunately, these DPDFs are currently available only in NLO precision.
We outline the methodology of the calculations and compare the new predictions to a variety of observables measured single- and double-differentially at HERA.
The new calculations allow for improved tests of factorisation assumptions in diffractive DIS, tests of DPDFs, and hard QCD studies. In the future, these new calculations will help to constrain the gluon distribution in DPDFs.
We will present two exclusive diffractive processes with NLO accuracy in the shockwave (CGC) formalism, which extends the linear BFKL picture to include high-energy saturation effects. We will detail the impact factors for the production of a forward dijet and for the production of a light neutral vector meson.
We study diffractive dijet production in lepton-nucleon scattering as a means to probe the phase space (Wigner) distribution of small-x gluons. We also discuss the experimental signature of the gluon orbital angular momentum.
The presence of a non-baryonic dark matter component in the Universe is inferred from the observation of its gravitational interaction. If dark matter interacts weakly with the Standard Model it would be produced at the LHC, escaping the detector and leaving a large missing transverse momentum as their signature. The ATLAS detector has developed a broad and systematic search program for dark matter production in LHC collisions. The results of these searches on the first 13 TeV data, their interpretation, and the design and possible evolution of the search program will be presented.
Many theories predict candidates to the dark matter particles that are light enough to be produced at the LHC. This talk presents the searches for dark matter at CMS in events with missing transverse energy, focusing on the recent results obtained using data collected in 2016.
The large set of proton-proton collision data recorded by CMS in 2016 at a centre-of-mass energy of 13 TeV is the basis for the first results on electroweak production of supersymmetric particles in LHC Run 2. Results for the pair production of charginos and neutralinos are presented based on the analysis of final states with one or more leptons and interpreted under several assumptions for the decay modes of the electroweak charginos.
Many supersymmetry models feature gauginos and also sleptons with masses less than a few hundred GeV. These can give rise to direct pair production rates at the LHC that can be observed in the data sample recorded by the ATLAS detector. The talk presents recent results of searches for chargino and neutralino direct production in final states with leptons using LHC Run 2 data.
I discuss the feasibility to search for supersymmetry in the decays of heavy Z' bosons, predicted by GUT-inspired U(1)' models, by investigating final states with charged leptons and missing energy in pp collisions at the LHC. I also investigate decays into pairs of the lightest MSSM neutralinos, which are Dark Matter candidates, and update the exclusion limits on the Z' mass, accounting for the inclusion of BSM decay modes.
We study the naturalness properties of the B − L Supersymmetric Standard Model (BLSSM) and compare them to those of the Minimal Supersymmetric Standard Model (MSSM) at both low (i.e., Large Hadron Collider) energies and high (i.e., unification) scales. By adopting standard measures of naturalness, we assess that, in presence of full unification of the additional gauge couplings and scalar/fermionic masses of the BLSSM, such a scenario reveals a somewhat higher degree of Fine-Tuning (FT) than the MSSM, when the latter is computed at the unification scale and all available theoretical and experimental constraints, but the Dark Matter (DM) ones, are taken into account. Yet, such a difference, driven primarily by the collider limits requiring a high mass for the gauge boson associated to the breaking of the additional U(1)B−L gauge group of the BLSSM in addition to the SU(3)C × SU(2)L × U(1)Y of the MSSM, should be regarded as a modest price to pay for the former in relation to the latter, if one notices that the non-minimal scenario offers a significant volume of parameter space where numerous DM solutions of different compositions can be found to the relic density constraints, unlike the case of the minimal structure, wherein only one type of solution is accessible over an ever diminishing parameter space. In fact, this different level of tension within the two SUSY models in complying with current data is well revealed when the FT measure is recomputed in terms of the low energy spectra of the two models, over their allowed regions of parameter space now in presence of all DM bounds, as it is shown that the tendency is now opposite, the BLSSM appearing more natural than the MSSM.
The production of prompt photons in association with jets in proton–proton collisions provides a testing ground for perturbative QCD (pQCD) with a hard colourless probe less affected by hadronisation effects than jet production. The measurements of the angular correlations between the photon and the jets can be used to probe the dynamics of the hard-scattering process. We present here a cross-section measurement using final states with at least one, two or three hadronic jets in addition to an isolated photon, differential in a wide range of kinematic variables describing the photon+jet production dynamic. Colour-coherence effects were investigated in events with a photon accompanied by two jets. The results are compared to recent theoretical predictions.
The production of multi-jet final states at hadron colliders probes pQCD at several mass scales. The processes can also be used to probe the gluon density function of the proton. The ATLAS collaboration has used multi-jets events, recorded at a center of mass energy of 8 TeV, to measure the transverse energy-energy correlations and its asymmetry and derive a measurement of the strong coupling constant.
Isolated photons with high transverse energy have been studied in $ep$ scattering with the ZEUS detector at HERA, using and integrated luminosity of 326 pb$^{-1}$. The kinematic region includes photon virtualities $10 < Q^2 < 350$ GeV$^2$. Photons with transverse energy $4< E_T^\gamma< 15$ GeV and pseudorapidity $-0.7 <\eta^\gamma< 0.9$ were measured with accompanying jets having transverse energy and pseudorapidity $2.5 < E_T^{\rm jet}<35$ GeV and $-1.5<\eta^{\rm jet}< 1.8$. Differential cross sections are presented for several different correlated variables: the fraction of the incoming photon energy and momentum that is transferred to the photon and the jet, the fraction of proton energy taken by the parton that interacts with the photon, and the azimuthal angle and the pseudorapidity difference between the prompt photon and the jet and between the prompt photon and the scattered electron. Comparisons with different theoretical calculations are made.
The OLYMPUS collaboration has recently published a precise
measurement of the positron-proton to electron-proton elastic
scattering cross section ratio, $R_{2\gamma}$, over a wide range of
the virtual photon polarization, $0.456<\epsilon<0.978$. This
provides a direct measure of hard two-photon exchange in elastic
lepton-proton scattering widely thought to explain the discrepancy
observed between polarised and unpolarised measurements of the
proton form factor ratio, $\mu_{p} G_{E}^{p}/G_{M}^{p}$. The
OLYMPUS results are significantly lower than theoretical
calculations that explain the observed discrepancy in terms of
two-photon exchange but are in good agreement with predictions based
on phenomenological fits to the available form factor data.
This presentation will briefly review the motivation for measuring
$R_{2\gamma}$ followed by a description of the OLYMPUS experiment
and analysis. In particular, the importance of soft two-photon
contributions from radiative corrections included in the analysis
will be shown. Then we will present the OLYMPUS results and compare
these with results from two similar, recent experiments. Finally,
various theoretical calculations will be compared with the
experimental results and conclusions drawn.
I am going to present results of application of recently formulated Transversal Momentum Dependent Factorisation (ITMD) to provide predictions for spectra of produced at LHC di-jets in p-Pb collisions. Furthermore I am going to compare the results to results obtained within High Energy Factorization (HEF). The results show that while the ITMD predicts significant enhancement of the cross section as compared to HEF the results for R pA are very similar within the two frameworks.
Jet quenching has been considered an important probe of the properties of the quark-gluon plasma (QGP) formed in the heavy ion collisions at RHIC and LHC. However, since d+Au collisions also show significant suppression of jet production, a thorough understanding cannot be achieved without the determination of other non-QGP nuclear medium effects. One of the competing factors involved, parton energy loss, demands measurements with cold nuclear matter in order to determine a baseline for comparison to the energy loss within the QGP. Using the Drell-Yan process, with its negligible final-state interaction, the energy loss of incoming quarks in cold nuclear medium can be cleanly studied. Using the 120 GeV proton beam from the Main Injector at Fermilab, E906/SeaQuest experiment consists of an instrumented magnetic spectrometer observing dimuons from fixed targets of H_2, D_2, C, Fe, and W. The SeaQuest collaboration has been collecting a high statistics event sample, starting in 2014 and continuing until the summer of 2017. The analysis of these data will provide a good opportunity for a clean measurement of energy loss effects in cold nuclear matter, since other nuclear effects (e.g., nuclear parton distributions) are expected to be minimal at the kinematics of the experiment, as compared to the previous E866 measurements. In this talk, the latest analysis will be described and the current results of the quark energy loss study will be presented.
BESIII collected the world largest data samples of 2.93, 0.482 and 0.567 fb-1 data at 3.773, 4.009 and 4.6 GeV, respectively. Based on these data samples, BESIII perform some analyses of $D^{0(+)}$, $D_{s}^{+}$ and $\Lambda_{c}^{+}$, which are important to understand the weak decay machanisms of charmed mesons and baryons. The leptonic decays of $D^{+} \to \tau^{+}\nu_{\tau}$ and $D_{s}^{+} \to \ell^{+}\nu_{\ell}$ are measured. The dynamics of $D^{+} \to \bar{K}^{0} e^{+}\nu_{e}$, $\pi^{0}e^{+}\nu_{e}$ and $K^{-}\pi^{+}e^{+}\nu_{e}$ are studied, and the parameters of the form factors and CKM matrix elements $|V_{cs(d)}|$ are extracted. In addition, the branching fractions for $D^{+} \to \bar{K}^{0} \mu^{+}\nu_{\mu}$, $\bar{K}^{0} e^{+}\nu_{e}$, $D_{s}^{+} \to \eta(')e^{+}\nu_{e}$ are also provided. The amplitude analysis of $D^{0} \to K^{-}\pi^{+}\pi^{+}\pi^{-}$ is performed. The asymetries of $D^{+} \to K_{\mathrm{S/L}}K^{+}(\pi^{0})$ and $D^{0} \to K_{\mathrm{S/L}}\pi^{0}(\pi^{0})$ decays are measured. The branching fractions for $D^{+} \to 2K_{\mathrm{S}}K^{+}$, $2K_{\mathrm{S}}\pi^{+}$, $D^{0} \to 2K_{\mathrm{S}}$, $3K_{\mathrm{S}}$ as well as $D^{0(+)} \to$ other 14 channels of $PP$ final states are determined. And, the measurement results of the Singly-Cabibbo-suppressed decays $\Lambda_{c}^{+} \to p\pi^{+}\pi^{-}$, $pK^{+}K^{-}$, $p\eta$ and $p\pi^{0}$, the Cabibbo-favored decays of $\Lambda_{c}^{+} \to nK_{\mathrm{S}}\pi^{+}$ and $\Sigma^{-}\pi^{+}\pi^{+}(\pi^{0})$ as well as the inclusive decay of $\Lambda + \mathrm{anything}$ have been obtained.
We report recent results on $B$ decays from Belle experiment at KEKB collider. $B \to D^{*} \tau \bar{\nu}_{\tau}$ mode is sensitive to probe New Physics such as charged Higgs or leptoquark, and the current world average of the branching ratio shows discrepancy from the Standard Model. Belle has performed a new measurement of this mode using tau decays to hadronic final states, which is essentially independent of previous measurements from Belle. With this method, we have measured the tau lepton polarization in $B \to D^{*} \tau \bar{\nu}_{\tau}$ for the first time. We also report the full angular analysis of $B \to K^{*} \ell^{+} \ell^{-}$ to extract form factor variables such as $P_{5}'$. The measurement is performed separately for $B \to K^{*} e^{+} e^{-}$ and $B \to K^{*} \mu^{+} \mu^{-}$ modes, which makes it possible to study lepton universality on these variables. The analyses are based on the full data set of Belle containing 772 million $B\bar{B}$ pairs.
Rare decays of $B$ mesons and $b$ hadrons provide sensitive indirect probes
of effects beyond the Standard Model (SM). In the SM, these decays are
forbidden at tree level and are therefore suppressed. In particular, the
$b \to s\ell\ell$ processes give access to many observables where effects of New
Physics can be observed. The LHCb experiment is designed for these
searches due to its large acceptance and trigger efficiency, as well as
its excellent invariant mass resolution and particle identification
capabilities. Recent results on these searches will be presented,
including the new measurement of the $B_{s} \to \mu\mu$ branching fraction.
In the Standard Model the different lepton families couple universally
to gauge bosons. Therefore, the ratio of branching fractions of decays
with different lepton flavours is predicted with a very good accuracy.
The universality of lepton couplings has been tested using the LHCb Run
1 dataset, resulting in some tensions with respect to the predicted
values. Lepton non-universality would be a major departure from the
Standard Model and may also be accompanied by lepton flavour violation.
Recent tests of lepton flavour universality and searches for lepton
flavour violation decays at LHCb will be presented.
We study the pseudoscalar and vector $B$ mesons decay constants within the framework of the light cone quark model (LCQM). LCQM deals with the wave function defined on the four-dimensional space-time plane defined by $x^{+} = x^{0} + x^{3}$ and includes the important relativistic effects that are neglected in the traditional constituent quark model. With the help of known values of constituent quark masses and the scale parameter $\beta$, we calculate the values of $B$ mesons decay constants, respectively. The decay constants of pseudoscalar and vector mesons are useful for controlling the meson semileptonic decay widths, hadronic couplings and form factors.
The Belle II experiment at the SuperKEKB collider is a major upgrade of the KEK “B factory” facility in Tsukuba, Japan aiming at an increase of the peak luminosity by a factor of 40. Commissioning of the SuperKEKB main ring took place in the first half of 2016. Phase 2 of the commissioning will start beginning of 2018 after the installation of the final focus system in the IR but still without the vertex detector system. Once machine operation in the nano-beam scheme is established the goal is to accumulate data for early physics analyses at different center-of-mass energies. In this talk we describe the physics program for this early data that will focus on bottomonium spectroscopy and low multiplicity studies like dark sector searches.
SHIP is a new general purpose fixed target facility, whose Technical Proposal has been recently reviewed by the CERN SPS Committee and by the CERN Research Board. The two boards recommended that the experiment proceeds further to a Comprehensive Design phase in the context of the new CERN Working group "Physics Beyond Colliders", aiming at presenting a CERN strategy for the European Strategy meeting of 2019. In its initial phase, the 400GeV proton beam extracted from the SPS will be dumped on a heavy target with the aim of integrating 2×1020 pot in 5 years. A dedicated detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow probing a variety of models with light long-lived exotic particles and masses below O(10) GeV /c2. The main focus will be the physics of the so-called Hidden Portals, i.e. search for Dark Photons, Light scalars and pseudo-scalars, and Heavy Neutrinos. The sensitivity to Heavy Neutrinos will allow for the first time to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which Baryogenesis and active neutrino masses could also be explained. Another dedicated detector will allow the study of neutrino cross-sections and angular distributions. ντ deep inelastic scattering cross sections will be measured with a statistics 1000 times larger than currently available, with the extraction of the F4 and F5 structure functions, never measured so far and allow for new tests of lepton non-universality with sensitivity to BSM physics.
We discuss the physics opportunities [1] which are offered by a next generation and multi-purpose fixed-target experiment exploiting the LHC beams. The multi-TeV LHC proton beam grants the most energetic fixed-target experiment ever performed, to study pp, pd and pA collisions at sqrt(s_NN) ~ 115 GeV. AFTER@LHC -- for A Fixed-Target ExperRiment -- gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular RHIC and the projects of electron-ion colliders.
With an internal (polarised) gas target or the "splitted" by a bent crystal, the typical instantaneous luminosity achievable with AFTER@LHC in pp and pA mode [1,2] surpasses that of RHIC by more than 3 orders of magnitude and is comparable to that of the LHC collider mode.
This provides a quarkonium, prompt photon and heavy-flavour observatory [1,3] in pp and pA collisions where, by instrumenting the target-rapidity region
or by using detectors such as LHCb and the ALICE muon arm, gluon and heavy-quark distributions of the proton, the neutron and the nuclei can be accessed at large x and even at x larger than unity in the nuclear case. The nuclear target-species versatility provides a unique opportunity to study the nuclear matter versus the hot and dense matter formed in heavy-ion collisions. With a reduced background compared to the collider mode, this will allow for the study of quarkonium excited states, in particular the chi(c) and chi(b) resonances. This will allow one to study gluon TMDs as suggested for instance in [4]. The fixed-target mode also has the advantage to allow for spin measurements with polarised targets, for instance single transverse-spin asymmetries for Drell-Yan pair production [5-7]. We will review all these aspects and show our latest simulation results.
References
[1] S. J. Brodsky, F. Fleuret, C. Hadjidakis and J. P. Lansberg, Phys. Rept. 108 522 (2013) 239. For a complete list of references see http://after.in2p3.fr/after/index.php/Recent_published_ideas_in_favour_of_AFTER@LHC
[2] C. Barschel, P. Lenisa, A. Nass, E. Steffens. Adv.High Energy Phys. 2015 (2015) 463141.
[3] L. Massacrier, B. Trzeciak, F. Fleuret, C. Hadjidakis, D. Kikola, J.P. Lansberg, H.-S. Shao. Adv.High Energy Phys. 2015 (2015) 986348.
[4] D. Boer and C. Pisano, Phys. Rev. D 86 (2012) 094007
[5] T. Liu and B.Q. Ma, Eur. Phys. J. C 72 (2012) 2037.
[6] M. Anselmino, U. D'Alesio, S. Melis. Adv.High Energy Phys. 2015 (2015) 475040.
[7] K. Kanazawa, Y. Koike, A. Metz, D. Pitonyak. Adv.High Energy Phys. 2015 (2015) 257934.
The 12 GeV CEBAF Upgrade at Jefferson Lab is greatly expanding the scientific capabilities for nuclear physics by doubling the maximum energy of the electron accelerator, constructing and operating a fourth experimental Hall, and upgrading the equipment in the existing three Halls. The early science program is underway with full, four Hall operations anticipated this year. The status of the construction and commissioning effort as well as the key science capabilities are presented.
The nuSTORM facility will provide \nu_e and \nu_\mu beams from the decay of low energy muons confined within a storage ring. The instrumentation of the ring, combined with the excellent knowledge of muon decay, will make it possible to determine the neutrino flux at the %-level or better. The neutrino and anti-neutrino event rates are such that the nuSTORM facility serving a suite of near detectors will be able to measure \nu_eN and \nu_\muN cross sections with the %-level precision required to allow the next generation of long-baseline neutrino-oscillation experiments to fulfil their potential. By delivering precise cross section measurements with a pure weak probe nuSTORM may have the potential to make measurements important to understanding the physics of nuclei. The precise knowledge of the initial neutrino flux also makes it possible to deliver uniquely
sensitive sterile-neutrino searches. The concept for the nuSTORM facility will be presented together with an evaluation of its performance. The status of the planned consideration of nuSTORM at CERN in the context of the Physics Beyond Colliders workshop will be summarised.
We present a quark-diquark model for nucleons where the light front wave functions are constructed form the soft-wall AdS/QCD prediction. The model is consistent with quark counting rule and Drell-Yan-West relation. The scale evolution of the PDFs are simulated by making parameters scale dependent. The model reproduces the scale evolution of unpolarized PDF for a wide range of energy scale and matches accurately with the HERAPDF15(nnlo), MSTW2008(nnlo), NNPDF21(nnlo). The helicity and transversity PDFs predicted in this model agree with phenomenological fits. The axial and tensor charges are shown to agree with experimental data.
We further investigate the transverse momentum $\bf{p}_\perp$ dependent parton distribution functions(TMDs) for both T-even and T-odd sector at the leading twist. In this model the pretzelosity TMDs, $h^\perp_{1T}(x,\bf{p}_\perp^2)$, are found to be negative for $u$ quark and positive for $d$ quark as predicted by phenomenology and most of the models e.g, Bag Model, CQM etc. Interestingly, though not explicit, our model has implicit $x-\bf{p}_\perp^2$ factorization which is assumed in phenomenological extraction of TMDs. The final state interaction produces a complex phase which can be included in LFWFs to calculate the Sivers functions $f^\perp_{1T}(x,\bf{p}_\perp^2)$ and Boer-Mulders functions $h^\perp_1(x,\bf{p}_\perp^2)$. We compare our results to the experimental data of SSAs and find reasonably good agreements.
We also investigate the more general five dimensional Wigner distributions for both $u$ and $d$ quarks in a proton and calculate the GTMDs. We present a detailed study of the quark orbital angular momentum and its correlation with the quark spin and the proton spin. The quark density distributions with the different polarizations of quarks and proton are presented in transverse momentum plane as well as in transverse impact parameter plane.
Polarized semi-inclusive deep inelastic scattering (SIDIS) plays a crucial role in understanding sea quark contributions to the proton spin through global analyses of spin-dependent parton distribution functions (PDFs). The shape of the strange quark polarization in particular has been shown to be dramatically different between analyses that include or exclude SIDIS data. The inclusion of SIDIS data, however, requires knowledge of fragmentation functions (FFs), which up until now have been fixed in all current analyses of SIDIS data to specific parameterizations determined from single-inclusive annihilation (SIA) and other quark to hadron fragmentation processes. In this talk, I will present results from a first ever simultaneous Monte Carlo analysis of polarized PDFs and FFs using DIS, SIA, and SIDIS data. I will also discuss in detail the extent to which current pion and kaon SIDIS data can distinguish between the valence and sea spin distributions of the proton.
Abstract:
We discuss a solution of the DGLAP parton evolution equations,
written in terms of Sudakov form factors to describe the branching
and no-branching probabilities, with a Monte Carlo method. We
show explicitly numerically, that this method reproduces exactly
the semi-analytical solutions also at NLO.
We discuss numerical effects of the kinematic boundary of resolvable
branchings on the resulting parton distribution functions. We show
explicitly, how this method can be used to determine
Transverse Momentum Dependent (TMD) parton distribution functions,
in addition to the usual integrated parton distributions functions.
We also show, that a very good fit to high precision HERA data can be
obtained over a large range in $x$ and $Q^2$ and present a first set of TMD parton dsitributions obtained from HERA precision data.
Naturalness arguments for weak-scale supersymmetry favour supersymmetric partners of the third generation quarks with masses not too far from those of their Standard Model counterparts. Top or bottom squarks with masses less than about one TeV can also give rise to direct pair production rates at the LHC that can be observed in the data sample recorded by the ATLAS detector. The talk presents recent ATLAS results from searches for direct stop and sbottom pair production, using data collected during the LHC Run 2.
Supersymmetric partners of top and bottom quarks are among the most promising candidates for the next-to-lightest supersymmetric particle. Searches for the pair production of top and bottom squarks have been performed in final states with 0, 1, or 2 charged leptons, jets, and missing transverse energy. The results are obtained using proton-proton collisions at sqrt(s) = 13 TeV, recorded by the CMS experiment in 2016.
The proton-proton collisions at sqrt{s} = 13 TeV at the LHC have increased the ATLAS sensitivity to production of strongly produced supersymmetric particles. If R-parity is not conserved, these particles may decay to jets and leptons, and lightest supersymmetric particles may decay into many leptons with or without missing transverse momentum. Several supersymmetric models also predict massive long-lived supersymmetric particles. Such particles may be detected through abnormal specific energy loss, appearing or disappearing tracks, displaced vertices, long time-of-flight or late calorimetric energy deposits. The talk presents recent results from searches of supersymmetry in resonance production, R-parity violating signatures and events with long-lived particles with the ATLAS detector using LHC Run 2 data.
Weak scale supersymmetry is one of the best motivated and studied extensions of the Standard Model. This talk summarises recent ATLAS results on searches for supersymmetric squarks and gluinos, including third generation squarks produced via the decay of gluinos. The searches involved final states containing jets (possibly identified as coming from b-quarks), missing transverse momentum and leptons. Results using collision data from the LHC Run 2 will be shown.
Results are presented from searches for strong production of supersymmetric particles in events with at least one leptons, jets, and missing transverse energy. The data set consists of proton-proton collisions at sqrt(s) = 13 TeV, recorded by the CMS experiment in 2016. The results are interpreted in the framework of several simplified models of gluino and squark pair production.
K+->pi+nunu is one of the theoretically cleanest meson decay where to look for indirect effects of new physics complementary to LHC searches. The NA62 experiment at CERN SPS is designed to measure the branching ratio of this decay with 10% precision. NA62 took data in pilot runs in 2014 and 2015 reaching the final designed beam intensity. The quality of data acquired in view of the final measurement will be presented.
We report the status of R measurement in 2-4.6 GeV at BESIII, and some new results from QCD studies, including: proton form factor with ISR, pi+pi- cross section and pion form factor with ISR, new measurement of J/psi parameters, e+ e- -> K+ K- cross sections in 2-3.08 GeV.
The NA48/2 experiment at CERN collected a very large sample of charged kaon decays into multiple final states. From this data sample we have reconstructed about 1500 events of the very rare decay K+- —>mu+- nu e+ e- over almost negligible background in the region with m(e+e-) above 140 MeV, which is of great interest in Chiral Perturbation Theory. We present the m_ee spectrum and a model-independent measurement of the decay rate for this region.
The first observation of about 5000 candidates, with a 5% background contamination, of this rare decay is reported by the NA48/2 experiment at CERN. From the analysis of 1.7 × 10^11 kaon decays collected in 2003–2004, the preliminary branching ratio in the full kinematic region is measured to be (4.22 ± 0.15) × 10^−6. The observed value is in perfect agreement with theoretical predictions based on Chiral Perturbation Theory.
Combined HERA data on charm production in deeply inelastic scattering have earlier been used to determine the charm-quark running mass $m_c(m_c)$ in the $\overline{MS}$ renormalisation scheme. The same data are used differentially as a function of the photon virtuality $Q^2$ to evaluate the charm-quark running mass at different scales to one-loop order, in the context of a next-to-leading order QCD analysis. The scale dependence of the mass is found to be consistent with QCD expectations and a graphical representation of the charm-quark mass running is obtained from data for the first time.
Heavy quark measurements in hadronic collisions are useful tests of perturbative Quantum Chromodynamics (pQCD) calculations given their large mass ($m_{c,b}\gg\Lambda_{\mathrm{QCD}}$). These measurements can also probe the gluon distribution in protons at a relatively large $Q^2$. At RHIC energies, $b$-quark production is dominated by the leading order gluon-gluon fusion in contrast of the production mechanism at Tevatron and LHC which are dominated by next-to-leading order processes. Different kinematic region of the nucleon parton distribution function is also accessed by RHIC measurements.
PHENIX has measured the production of $B$-mesons through the $B \rightarrow J/\psi \rightarrow \mu^{+}\mu^{-}$ decays in $1.2 < |y| < 2.2$ rapidity at 200 and 510 GeV $p+p$ collisions, by the analysis of displaced vertex of muons with the Forward Silicon Vertex Detector (FVTX). These measurements can access $B$-mesons with $p_{\mathrm{T}} > 0$ allowing a direct measurement of $b\bar{b}$ total cross section. The PHENIX $p + p$ measurements will be presented in comparison to Tevatron and LHC results, providing a understanding of the energy dependent $B$ hadron production and the transition between LO to NLO dominant $b$-quark production.
Heavy flavor particles produced in LHC pp collisions at 7, 8, and 13 TeV constitute an excellent opportunity to test the standard model and probe for new physics effects. Recent results by the CMS Collaboration on heavy flavor production and decays are presented.
In this talk, we present our recent work on heavy flavor production in heavy ion collisions. We develop a version of Soft Collinear Effective Theory (SCET) which includes finite quark masses, as well as Glauber gluons that describe the interaction of collinear partons with QCD matter. With such a framework (labeled SCET$_{\mathrm{M},\mathrm{G}}$), we derive the massive splitting functions in the vacuum and the QCD medium associated with heavy quarks. The numerical effects due to finite quark masses are sizable and our results are consistent with the traditional approach to parton energy loss in the soft gluon emission limit. In addition, we present a new framework for including the medium-induced full splitting functions consistent with next-to-leading order calculations in QCD for inclusive hadron production. We show numerical results for the suppression of $D$- and $B$-mesons in heavy ion collisions and find good agreements with the available data from the LHC.
Charm and bottom quarks are produced in hard processes, in the early stages of relativistic hadron-hadron collisions. Due to their large masses, their initial production yield is practically unaffected by the later stages of the reaction. Therefore they provide us with unique means for understanding several aspects of Quantum Chromodynamics, from pure pQCD processes, to energy loss and collective motion within a nuclear medium created in heavy-ion collisions.
Measurements of spectra in $pp$ collisions serve as a benchmark for theory calculations as well as a reference for collisions of heavier systems. Multiplicity-dependence of the production may reveal the importance of multi-parton interactions, the interplay between the hard and soft regime of the interactions, as well as the connection between open and hidden production of heavy-flavour. Measurements in $p$-Pb collisions also account for cold nuclear effects, thus providing baseline for heavy-ion measurements. Correlations of $D$ mesons and hadrons reveal charm fragmentation properties as well as possible collective effects in $p$-Pb collisions.
In this presentation we show recent open heavy-flavour results from pp collisions at $\sqrt{s} = 5.02$, 7 and 8 TeV, and $p$-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV, collected with the ALICE detector during LHC Run 1. Hadrons containing charm and bottom are reconstructed via the semileptonic as well as hadronic decays. Charm measurements down to $p_{\mathrm{T}} = 0$ will be shown for $pp$ and $p$-Pb collisions. Prospects for heavy-flavour measurements in Run 2, with an increased energy and luminosity, will also be discussed.
Deeply Virtual Compton Scattering (DVCS), in which the electron scatters from a parton inside a hadron and a high energy photon is produced as a result, is considered the golden channel for accessing Generalised Parton Distributions (GPDs), in a form of hadron tomography. One can interpret GPDs as functions relating the transverse position of partons to their longitudinal momentum and as such they carry sensitivity to the spin structure of the hadron. Extraction of GPDs is highly non-trivial and requires measurements of a range of complementary observables across large regions of phase space. Recently, a series of such measurements at Jefferson Lab (JLab), USA, have provided a wealth of new DVCS data in the valence quark regime of the nucleon, while the experimental programme with the JLab upgraded 11 GeV beam will greatly extend the dataset in its kinematic reach. This enables a global analysis of the data, dramatically constraining the extraction of GPDs and deepening our understanding of the three-dimensional structure of the nucleon.
Deeply Virtual Compton Scattering (DVCS) is the easiest reaction that accesses the Generalized Parton Distributions (GPDs) of the nucleon. GPDs offer the exciting possibility of mapping the 3-D internal structure of protons and neutrons by providing a transverse image of the constituents as a function of their longitudinal momentum.
A vigorous experimental program is currently pursued at Jefferson Lab (JLab) to study GPDs through DVCS. New results from Hall A will be shown and discussed. Special attention will be devoted to the applicability of the GPD formalism at the moderate values of momentum transfer (Q2) available at JLab.
We will conclude with a brief overview of additional DVCS experiments under analysis and planned with the future Upgrade of JLab to 12 GeV.
Wide-Angle Compton Scattering (WACS) on the proton is a powerful and under utilized probe of the transverse structure of the nucleon, which is complementary to high-$Q^{2}$ elastic electron-nucleon scattering. By demanding that all of the momentum transferred to the proton be shared among its constituents, unlike in inclusive or deeply virtual reactions, one gains access to information on the high $-t$ axial, vector and tensor proton structure in the valence regime.
The small cross section associated with WACS poses a significant experimental challenge, and the requirements for relatively high photon energy and very high luminosity make Jefferson Lab (JLab) the ideal facility to explore this reaction. Two experiments took place during the 6 GeV era at Jefferson Lab, which mapped out unpolarized and polarized observables up to $-t$ of several GeV$^2$. New experiments are planned at the post-upgrade 12 GeV JLab, preparations for which are already at an advanced stage. A brief overview of the earlier experiments and results will be discussed, before moving on to an exploration of plans for the new experiments and crucially what they can reveal about the non-perturbative transverse structure of the proton and the underlying quark-gluon dynamics.
Key properties of the nucleon are encoded in the correlation between their longitudinal momentum and their transverse position, such as the orbital angular momentum. This correlation is expressed through Generalized Parton Distributions (GPDs), which can be understood as spatial densities at different values of the longitudinal momentum of the quark. Validation of our understanding of hard exclusive reactions ($\pi^+$, $K^+$, $\pi^0$, $\gamma$) is an essential aspect towards such 3D hadron imaging and potential future flavor decomposition. The key to extracting GPDs from experiment is QCD factorization theorems. To validate the meson factorization theorems and potentially extract flavor separated GPDs from experiment, one has measure the separated longitudinal and transverse cross sections and their $t$ and $Q^2$ dependencies. Recent data and prospects for deep exclusive pion, both charged and neutral, and kaon electroproduction are presented, which conceptually would allow for flavor separations.
The HERMES experiment collected a wealth of deep-inelastic scattering data using the 27.6 GeV polarized lepton beam at HERA and various pure gas targets, both unpolarized and polarized. This allowed for a series of diverse measurements. Among them are measurements on hard exclusive meson production, which provide information on generalized parton distributions (GPDs), in a com-plementary way to, e.g., deeply virtual Compton scattering. Access to these GPDs is possible through the measurement of helicity amplitude ratios. Helicity amplitude ratios from exclusive ρ0 production on transversely polarized protons are presented and discussed as well as compared to a theoretical model [1, 2].
[1] S. V. Goloskokov and P. Kroll, Eur. Phys. J. C 50, 829 (2007).
[2] S. V. Goloskokov and P. Kroll, Eur. Phys. J. C 53, 367 (2008).
From the mid-2020s, the Large Hadron Collider will run as High Luminosity LHC (HL-LHC) with a centre of mass energy of 14 TeV and an instantaneous luminosity of 5-7 x 10^34 cm^-2 s^-1. It aims to collect a total integrated luminosity of 3000 fb-1 by about 2037.
The unprecedented amount of data collected by the upgraded ATLAS detector at the HL-LHC will be used to make precision measurements of the 125 GeV Higgs boson. In addition final states including Higgs bosons can be used to probe for beyond-the-Standard-Model physics and for search for rare processes.
Observation of di-Higgs production, pp—>HH, can be used to constrain the parameter lambda in the Higgs potential and is one of the key physics drivers for the HL-LHC programme. However due to the small predicted cross section for HH production many final states must be considered to gain sensitivity to di-Higgs production at the HL-LHC.
In this talk we present the studies on the prospects for precision measurements of the Higgs boson and searches for rare Higgs boson processes at the upgraded ATLAS detector at the HL-LHC. Also, prospects to observe di-Higgs production at the upgraded ATLAS detector at the HL-LHC are reported and discussed.
We discuss the physics reach of LHeC and FCC-he for BSM Higgs and di-Higgs production. In particular we also discuss invisible Higgs decay scenario. A detector level studies with speculated parameters have been performed for these channels.
The Georgi-Machacek (GM) model is one of many beyond standard model scenarios
with an extended scalar sector which can group under the custodial SU(2) symmetry
into a fiveplet, a triplet, and two singlets. We study the prospects for detecting the doubly-charged Higgs boson ($\rm H_5^{\pm\pm}$) through the vector boson fusion with same-sign leptons decay channel at the Large Hadron Electron Collider (LHeC).
The discovery significance and necessary luminosity are presented as a function of the triplet vaccum expectation value.
In this talk I will give an overview over the searches for sterile neutrinos at electron-proton colliders, discuss the most important signatures, and present the complementarity with searches at proton-proton and electron-positron colliders.
Measurements of open beauty and charm production cross sections in deep inelastic $ep$ scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections for beauty and charm production are obtained in the kinematic range of photon virtuality 2.5 ≤ Q$^2$ ≤ 2000 GeV$^2$ and Bjorken scaling variable 3 · 10$^{−5}$ ≤ x ≤ 5 · 10$^{−2}$. The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined data are compared to perturbative QCD predictions.
We present the possibility of intrinsic (non-perturbative) charm in parton distribution functions (PDF) of the proton, within the context of the CT14 next-to-next-to-leading order (NNLO) global analysis. Different models of intrinsic charm are analysed and compared. The correlations between the value of the charm-quark mass and the allowed amount of intrinsic charm is also discussed.
We present an updated and improved extraction of the low-$x$ gluon distribution from the HERA and LHCb (7 TeV and preliminary 13 TeV) exclusive $J/\psi$ production data in the context of $k_T$ factorisation. Critically, we use a more precise expression for the photon flux and re-calculate the rapidity gap survival factors.
In collinear factorisation exclusive $J/\psi$ photoproduction receives large perturbative corrections at NLO which prevents immediately using the coefficient function to extract a gluon PDF from the data. Attempts to understand and overcome the problems caused by the large perturbative corrections are discussed.
The small-$x$ gluon in global fits of parton distributions is affected by large uncertainties from the lack of direct experimental constraints. In this work we provide a precision determination of the small-$x$ gluon from the exploitation of forward charm production data provided by LHCb for three different centre-of-mass (CoM) energies: 5 TeV, 7 TeV and 13 TeV. The LHCb measurements are included in the PDF fit by means of normalized distributions and cross-section ratios between data taken at different CoM values, $R_{13/7}$ and $R_{13/5}$. We demonstrate that forward charm production leads to a reduction of the PDF uncertainties of the gluon down to $x \approx 10^{-6}$ by up to an order of magnitude, with implications for high-energy colliders, cosmic ray physics and neutrino astronomy.
I discuss the impact of recent measurements of top-pair differential distributions from ATLAS and CMS at $\sqrt{s}=8$ TeV on the gluon parton distribution function (PDF). The new data is included in a global QCD analysis of PDFs at next-to-next-to-leading order (NNLO) accuracy, based on the NNPDF methodology. I comment on the compatibility between ATLAS and CMS measurements and I show how a suitable choice of differential distributions can maximize the reduction of the gluon uncertainty at large momentum fractions. I discuss some implications in gluon-initated processes which are relevant in searches for new physics.
We consider an observable very sensitive to the non-zero intrinsic charm (IC) contribution to the proton density.
It is the ratio between the differential cross sections of the photon or $Z$-boson and $c$-jet
production in the $pp$ collision, $\gamma(Z) + c$, and the $\gamma(Z)$ and the $b$-jet production.
It is shown that this ratio can be approximately flat or increasing at large $\gamma(Z)$ transverse momenta $p_T$
and their pseudo-rapidities $1.5 < \eta < 2.4$ if the IC contribution is taken into account.
On the contrary, in the absence of the IC this ratio decreases as $p_T$ grows.
We also present the ratios of the cross sections integrated over $p_T$ as a function of the IC probability $w$.
It is shown that these ratios are mostly independent on the theoretical uncertainties, and such predictions could
therefore be much more promising for the search for the intrinsic charm signal at the LHC compared to the predictions
for $p_T$-spectra, which significantly depend on these uncertainties.
A correct modelling of the underlying event in proton-proton collisions is important for the proper simulation of kinematic distributions of high-energy collisions. The ATLAS collaboration extended previous studies at 7 TeV with a leading track or jet or Z boson by a new study at 13 TeV, measuring the number and transverse-momentum sum of charged particles as a function of pseudorapidity and azimuthal angle in dependence of the reconstructed leading track. These measurements are sensitive to the underlying-event as well as the onset of hard emissions. The results are compared to predictions of several MC generators.
Inclusive four-jet events produced in proton--proton collisions at a center-of-mass energy of 7 TeV have been analyzed for the presence of hard double parton scattering collected with the ATLAS detector. The contribution of hard double parton scattering to the production of four-jet events has been extracted using an artificial neural network. The assumption was made that hard double parton scattering can be represented by a random combination of dijet events. In addition, a sample enriched with double parton scattering events was extracted and several characteristics of these events were studied. The measurements have been compared to different MC generator predictions.
We present results on the measurement of the underlying event at 13 TeV using leading tracks, jets, and Drell-Yan processes. In addition measurements of forward-backward particle correlations and the rapidity gap fraction are presented. Finally results on charged particle multiplicity and transverse momenta distributions are shown.
We present recent results on Double Parton Scattering (DPS) studies using data collected during Run 1 and Run 2 of the LHC with the CMS experiment. Double parton scattering is investigated in several final states including vector bosons and multi-jets. Measurements of observables designed to highlight the DPS contribution are shown and compared to MC predictions from models based on multiple partonic interactions (MPI) phenomenology.
The CASTOR calorimeter at CMS measures the energy of particles emitted with pseudorapidity between -5.2 and -6.6. It has been operating since the startup of the LHC in 2009 and has taken data in pp, pPb, and PbPb collisions at various centre-of-mass energies during run 1 and run 2. In this presentation we give an overview of some important and unique results obtained with CASTOR, with emphasis on the forward energy flow and jet production in pp collisions with $\sqrt{s} =$ 13 TeV and pA collision with $\sqrt{s} =$ 5 TeV. These results are compared to various models for the underlying event and parton shower dynamics.
We use spinor helicity formalism to calculate production of 3 partons of any polarization in DIS at small x. The target hadron or nucleus is treated as a classical color field from which the partons scatter. We then study the azimuthal angular correlations between the produced partons and show that it is a sensitive probe of gluon saturation at small x. We finally relate this process to Double Parton and Triple Parton Interactions in a proton at large x.
We present an update of the first-ever study of 4-jet production in kt-factorization. We discuss how to supplement it with parton showers using the CASCADE Monte Carlo program and discuss the evidence for the need of contributions from Multi Parton Interactions to properly describe the data over the full phase space.
The discovery of a Higgs boson at the Large Hadron Collider (LHC) motivates searches for physics beyond the Standard Model (SM) in channels involving coupling to the Higgs boson. A search for a massive resonance decaying into a standard model Higgs boson (h) and a W or Z boson or two a standard model Higgs bosons is performed. Final states with different number of leptons or photons and where in many cases at least one Higgs decays into a b-quark pair are studied using different jet reconstruction techniques which are complementary in their acceptance for low and high mass transverse momentum. This talk summarizes ATLAS searches for diboson resonances including at least one h boson in the final state and searches for resonant and non-resonant di-Higgs production with LHC Run 2 data.
Beyond the standard model theories like Extra-Dimensions and Composite Higgs scenarios predict the existence of very heavy resonances compatible with a spin 0 (Radion),spin 1 (W’, Z’) and spin 2 (Graviton) particle with large branching fractions in pairs of standard model bosons and negligible branching fractions to light fermions. We present an overview of searches for new physics containing W, Z or H bosons in the final state, using proton-proton collision data collected with the CMS detector at the CERN LHC. Many results use novel analysis techniques to identify and reconstruct highly boosted final states that are created in these topologies. These techniques provide increased sensitivity to new high-mass particles over traditional search methods.
Searches for high mass BSM scalars have been carried out with the CMS detector at LHC, based on pp collision data collected at centre-of-mass energies of 7, 8, and 13 TeV. The talk presents the latest results and gives a brief review of earlier results.
Searches for BSM particles using the 126 GeV Higgs boson have been carried out with the CMS detector at LHC, based on pp collision data collected at centre-of-mass energies of 7, 8, and 13 TeV. The talk presents the latest results and gives a brief review of earlier results.
Several theories beyond the Standard Model, like the 2HDM, predict the existence of high mass neutral and charged Higgs particles. Searches for such additional Higgs bosons have been performed in bosonic and fermionic decay modes of the additional Higgs bosons. This talk summarizes ATLAS searches for heavy Higgs boson resonances with LHC Run 2 data collected in 2015 and 2016.
Hadron spectroscopy is one of the most important physics goals of BESIII. Since 2009, BESIII has collected 1.3 10^8 J/psi and 0.410^8 of psi', which are the world's largest data samples of J/psi and psi' from e+e- collision. These data are being used to make a variety of interesting and unique studies of QCD exotics (e.g. gluonic excitations and multiquarks) and light meson decay dynamics. Several recent results on light hadron spectroscopy and light hadron decays will be reported, mostly eta' related, including:
1, amplitude analysis of eta'->3pi
2, study of eta'->gamma pi+ -pi- decays
3, observation of the doubly radiative decay eta' -> gamma gamma pi0
The NA48/2 experiment presents a final result of the charged kaon semileptonic decays form
factors measurement based on 4.28 million $K^\pm_{e3}$ and 2.91 million $K^\pm_{\mu 3}$ selected
decays collected in 2004. The result is competetive with other measurements in $K^\pm_{\mu 3}$
mode and has a smallest uncertainty for $K^\pm_{e3}$, that leads to the most precise
combined $K^\pm_{l3}$ result and allows to reduce the form factor uncertainty of $|V_{US}|$.
At short distance between partons, double parton scattering overlaps with loop contributions to standard single hard scattering. Responsible for this is the splitting of one parton into two, and different choices for the partitioning of these contributions between single and double scattering give rise to different cross section formulae and to different evolution equations for the double parton distributions. We present a consistent scheme to separate single from double hard scattering and illustrate numerically the relative importance of the respective contributions.
Double parton scattering (DPS) describes two colliding hadrons having interactions in the form of two hard processes, each initated by a separate set of partons. Just as for single parton scattering, the resummation of soft gluons gives rise to a soft function, which is a necessary ingredient for obtaining rapidity evolution equations. For various regions of phase space, I derive the rapidity evolution and the scale evolution of double transverse momentum dependent parton distribution functions (DTMDs) as well as of the pT-resummed cross section for double Drell-Yan like processes. This contributes to a framework that could be used for phenomenological DPS studies including resummation.
The BABAR Collaboration has an intensive program studying hadronic cross sections in low-energy e+e- annihilations, accessible via initial-state radiation.
Our measurements allow significant improvements in the precision of the
predicted value of the muon anomalous magnetic moment.
These improvements are necessary for shedding light on the current ~3 sigma
difference between the predicted and the experimental values.
We have published results on a number of processes with two to six hadrons in the final state, and other final state are currently under investigation.
We report here on the most recent results obtained by analysing the entire BABAR dataset, in particular the measurement of the e+e- -> pi+pi-pi0pi0, which is one of the least known contribution to the cross section in the energy region between 1 and 2 GeV.
We also present the measurement of the pi+pi-eta, and of the full set of final states with two kaons and two pions.
Measurements of the transverse polarization of lambda hyperons with
respect to their production plane are sensitive to the polarizing
fragmentation function $D_{1T}^{\perp \Lambda/q}$. This fragmentation
function might be part of the explanation of the significant
transverse polarization of Lambda in p+p scattering. It can also be seen
as the hadronization analogue to the Sivers function, since it
describes the transverse momentum dependent transverse polarization of
the hyperon. As a chiral-even, naive time-reversal-odd function it
also allows to test universality, in particular the sign, of these
functions between different processes.
We present the first observation of the transverse polarization of
Lambda hyperons in e+e- annihilation at or near $\sqrt{s}=10.58$ GeV using a dataset of about 800fb$^-1$ integrated luminosity collected by the Belle detector.
The transverse spin transfer of $\Lambda$ hyperons in proton+proton collisions can provide insights into the polarized fragmentation function and the transversity distribution of the nucleon.
In this contribution, we report the first measurement of the transverse spin transfer of $\Lambda$ and $\bar{\Lambda}$ hyperons along the polarization direction of the outgoing quark in transversely polarized proton+proton collisions at RHIC.
The data were taken in 2012 with the STAR detector at $\sqrt{s}=200\,\mathrm{GeV}$ with an integrated luminosity of $18.4\, \mathrm{pb}^{-1}$ and covered hyperon transverse momenta up to $8\,\mathrm{GeV/c}$.
The beam polarization was about 63% during our data taking period.
The COMPASS experiment at CERN, as part of its programme addresses the exploration of the transverse spin structure of the nucleon by measuring spin (in)dependent azimuthal asymmetries in semi-inclusive DIS and, recently, also in Drell-Yan processes. Between 2002 and 2010 COMPASS performed a series of SIDIS measurements, using a longitudinally polarized muon beam impinging on transversely polarized $^6LiD$ or $NH_3$ targets. Drell-Yan measurements with a $\pi^-$ beam interacting with a transversely polarized $NH_3$ target started with the 2015 run and will be continued in 2018. The measurement of the Sivers and other azimuthal asymmetries at practically the same hard scale in polarized SIDIS and Drell-Yan at COMPASS provides a unique possibility to test predicted in QCD (pseudo-)universal features of transvers momentum dependent parton distribution functions. The main focus of this talk will be set on the results of the first ever polarized Drell-Yan measurements performed by COMPASS and related SIDIS results.
The Sivers function describes the correlation between the transverse spin of a nucleon and the trans-
verse motion of its partons. As such, a nonzero Sivers e?ect for gluons could be a signature of
their nonzero orbital angular momentum inside the nucleon. COMPASS has collected data of semi-
inclusive deep inelastic scattering by impinging 160 GeV=c muons on transversely polarised proton
and deuteron targets. The gluon Sivers asymmetry is extracted from a high-pT hadron pair sample
with the use of monte carlo simulations and the a neural network approach. The results of a similar
analysis for a Collins-like asymmetry for gluons will also be given.
I will first try to convince you that the application of TMD factorization at small x has been well justified at tree level and NLO level. Then I will show that there is very rich polarization dependent phenomenology at small x. In particular, the small x asymptotic behavior of gluon TMDs inside an unpolarized and transversely polarized target will be discussed. The small x gluon tomograph induced by the saturation effect will also be addressed.
Within the QCD parton model approach, the quark structure of the polarized nucleon can be parametrized in terms of spin and quark transverse momentum dependent parton distribution functions while the hadronization mechanism is described by fragmentation functions. Specific convolutions of these objects can be accessed through the measurement of longitudinal spin-dependent asymmetries in semi-inclusive DIS processes. For this purpose COMPASS has performed a series of SIDIS measurements using 160-200 GeV/c polarized muons scattering off longitudinally polarized deuteron ($^{6}LiD$) and proton ($NH_3$) targets. In addition to already published single charged hadron production deuteron azimuthal asymmetries, COMPASS has recently extracted the whole set of proton asymmetries in this channel, as well as the asymmetries in di-hadon production. In this talk selected COMPASS results will be presented along with former results obtained by other collaborations and relevant theoretical model predictions.
Jefferson Lab Electron Ion Collider (JLEIC) is a proposed realization of the Electron-Ion Collider project in the US. It builds on the existing CEBAF accelerator as the full energy electron injector and adds an ion complex to achieve the luminosity and energy requirements. The current status of the design will be discussed.
The possibility of a very high energy electron-proton (VHEeP) collider with a
centre-of-mass energy of 9 TeV has been presented previously. Further developments are here discussed, summarising the results from a recent publication and highlighting opportunities for more investigation. At the VHEeP collider, with a centre-of-mass energy 30 times greater than HERA, parton momentum fractions, $x$, down to about $10^{-8}$ are accessible for photon virtualities, $Q^2$, of 1 GeV$^2$. The energy dependence of hadronic cross sections at high energies, such as the total photon-proton cross section, which has synergy with cosmic-ray physics, can be measured and QCD and the structure of matter better understood in a region where the effects are completely unknown. Searches at high $Q^2$ for physics beyond the Standard Model will be possible, in particular the significantly increased sensitivity to the production of leptoquarks. Other additional possibilities for future DIS experiments using a high energy electron beam accelerated using plasma wakefields are also discussed. Such beams could revitalise the field of DIS and investigate e.g. the proton density at very high x in fixed-target experiments.
A precision measurement of jet cross sections in neutral current deep-inelastic scattering for photon virtualities $5.5 < Q^2 < 80$ GeV$^2$ and inelasticities $0.2 < y < 0.6$ is presented, using data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 290 pb$^{−1}$. Double-differential inclusive jet, dijet and trijet cross sections are measured simultaneously and are presented as a function of jet transverse momentum observables and as a function of $Q^2$. Jet cross sections normalised to the inclusive neutral current DIS cross section in the respective $Q^2$ -interval are also determined. Previous results of inclusive jet cross sections in the range $150 < Q^2 < 15000$ GeV$^2$ are extended to low transverse jet jet momenta $5 < P_T < 7$ GeV. The data are compared to predictions from perturbative QCD in next-to-leading order in the strong coupling, in approximate next-to-next-to-leading order and in full next-to-next-to-leading order. Using also the recently published H1 jet data at high values of $Q^2$, the strong coupling constant $\alpha_s(M_Z)$ is determined in next-to-leading order.
Measurements of inclusive jet cross sections have been performed by a number of experiments in proton—proton, proton—anti-proton, and electron—proton collisions and at different center-of-mass energies. Since inclusive jets are directly sensitive to the strong coupling constant, and exhibit a high sensitivity to the gluon content of the proton, a thorough understanding of the available experimental data is needed for precision QCD phenomenology. For instance, the strong coupling constant, α_s(Mz), has been determined recently by the H1, CMS and D0 experiments from their inclusive jet data.
Here, we present a study of the methodology of the α_s-determinations as used by the H1, CMS and D0 Collaborations. We also investigated data by the ATLAS, CDF, STAR and ZEUS Collaborations. Using predictions at NLO QCD, values of the strong coupling constant are determined from each individual data set, and from a simultaneous fit to all inclusive jet data, which improves the experimental precision as compared to an extraction from a single experiment only. The study examines the consistency of the data sets and paves the way for precision QCD phenomenology using inclusive jet data in the future.
We present measurements of multi-differential Jet cross sections over a wide range in transverse momenta from inclusive jets to multi-jet final states. We present studies on the impact these measurements have on the determination of the strong coupling alphas as well as on parton density functions.
The production of inclusive jets and di-jets at hadron colliders provides a stringent test of perturbative QCD at the highest energies. The process can also be used to probe the gluon density function of the proton.
The ATLAS collaboration has measured the inclusive jet production cross section in 20.3 /fb of data collected at a center-of-mass energy of 8TeV and in 3.2 /fb of data collected at a center-of-mass energy of 13TeV. The measurements have been performed differentially in jet rapidity and transverse momentum. The collaboration also presents a first measurement of the di-jet cross section at a center-of-mass energy of 13TeV as a function of the di-jet mass and rapidity. The results have been compared with state-of-the-art theory predictions at NLO in pQCD, interfaced with different parton distribution functions.
While properties of the jets are typically directly using the jet momenta, we present here a complementary approach, studying the jet production rates at different resolution scales. In particular, we present a measurement of the splitting scales occuring in the kt jet-clustering algorithm for final states containing a Z-boson candidate at a centre-of-mass energy of 8 TeV. The measurement is based on charged-particle track information, which is known with excellent precision in the pT-region relevant for the transition between the perturbative and the non-perturbative regimes. The data are corrected for detector effects and are compared to state-of-the-art Monte Carlo predictions.
We propose to consider the production of a forward J/Psi and a backward jet at the LHC, similarly to Mueller Navelet jet production. We will present a feasibility study for our process and give predictions in the BFKL framework.
Beams of relativistic heavy ions accompanied by a large flux of equivalent photons, and photon-induced reactions are the dominant interaction mechanism in heavy-ion collisions when the colliding nuclei have transverse separation larger that the nuclear diameter. In these ultra-peripheral collisions (UPC) the photon can provide a clean probe of the partonic structure of the nucleus analogous with deep inelastic scattering. This talk presents measurements of dijet production in ultra-peripheral Pb+Pb collisions performed with the ATLAS detector. Events are selected using requirements on rapidity gaps and forward neutron production to identify the photo-nuclear processes. The relatively clean environment of these events allows for measurements in a region of x and Q^2 where significant nuclear PDF modifications are expected to be present and not strongly constrained by previous measurements.
Recently, a new family of observables consisting of azimuthal-angle generalised ratios was proposed in a kinematical setup that resembles the usual Mueller-Navelet jets but with an additional tagged jet in the central region of rapidity. Here, we calculate the, presumably, most relevant higher order corrections to the observables. The corrections appear to be mostly moderate giving us confidence that the recently proposed observables are actually an excellent way to probe the BFKL dynamics at the LHC. Furthermore, we allow for the jets to take values in different rapidity bins in various configurations such that a comparison between our predictions and the experimental data is a straightforward task.
I am going to present predictions for spectra of very forward single inclusive jet production in proton-proton collisions obtained within High Energy Factorization.
The calculations are performed in HEF are compared to Pythia MC generator. The options available in Pythiia allow us to study importance of various effects like multiple interactions, hadronization.
We explicitly show that once the hard cut on transversal momenta in Pythia are applied the result for considered spectra of jet is very similar up to normalization to the BK based calculation while when the soft cut is applied the result is consistent up to normalization to the BFKL result.
During the last two years the LHC produced pp collisions at the record center-of-mass energy of 13 TeV. The sensitivity of searches for new phenomena with a high mass scale greatly benefited from the energy increase with respect to the LHC run-1 data. Events with two hadronic jets in the final state are of particular interest: new phenomena produced in parton collisions are likely to produce final states with (at least) two partons. In this talk several searches performed by the ATLAS collaboration are presented. The very high mass and the low mass regions have both been investigated, by exploiting dedicated signatures and, in case of the latter, new techniques to overcome trigger limitations. Results and perspectives for these searches will be presented.
This presentation will be focused on searches for new physics with dijets at CMS using data collected in the LHC Run 2. Both heavy and light dijet mass resonances will be investigated. Results from the dijet angular analysis will also be discussed.
The high-precision HERA data allow searches for "beyond the Standard Model" contributions to electron-quark scattering up to TeV scales. Combined H1 and ZEUS measurements of inclusive deep inelastic cross sections in neutral and charged current $ep$ scattering are considered, corresponding to a luminosity of around 1 fb$^{−1}$. A new approach to the beyond the Standard Model analysis of the inclusive $ep$ data is presented; simultaneous fits of parton distribution functions and contributions of "new physics" processes are performed. Considered are possible deviations from the Standard Model due to a finite radius of quarks, described within the quark form-factor model, and due to new electron-quark interactions in the framework of $eeqq$ contact interactions (CI). The resulting 95% C.L. upper limit on the effective quark radius is 0.43 $\cdot$ 10$^{−16}$ cm. The limits on the CI mass scale extend up to 10 TeV depending on the CI scenario.
We show the effects of the inclusion of Photon-Initiated processes in the di-lepton channel.
We include the contribution of quasi-real photon through the Equivalent Photon Approximation, of real photons through the recently released QED PDFs, and (as novelty) of the mixed real- quasi-real photons interaction.
We comment on the systematic uncertainties arising from the inclusion of those terms as predicted by different PDF collaborations.
We show the consequences of the inclusion of all the aforementioned terms in BSM searches for Z' bosons in the di-lepton channel.
The NA62 experiment at CERN collected a large sample of charged kaon decays in flight with a minimum bias trigger in 2007. Upper limits on the rate of the charged kaon decay into a muon and a heavy neutral lepton (HNL) obtained from this data are reported for a range of HNL masses.
Differential cross sections are presented for the prompt and non-prompt production of the hidden-charm state $X(3872)$ and of $\psi(2S)$, in the decay mode $J/\psi \pi^{+} \pi^{-}$, measured at $\sqrt{s} = 8$ TeV by the ATLAS detector at LHC. In the non-prompt production, the data suggest the presence of a short-lived component, which my be due to $B_{c}$ decays. The dipion invariant mass in both $X(3872)$ and $\psi(2S)$ are measured and compared to theoretical predictions.
BESIII has collected about 9 pb$^{-1}$ electron positron annihilation sample at 4.0–4.6 GeV. With this large sample, new searches for exotic states and precise studies of line-shape during this energy region are performed. We present the measurements of cross sections with final states $\pi^{+} \pi^{-} \psi(2S)$, $K \bar{K} J/\psi$, $\pi^{+} \pi^{-} h_{c}$, $\pi^{+} \pi^{-} J/\psi$, $\gamma \eta_{c}$, $\eta Y(2175)$, and $\pi^{0} \pi^{0} \psi(2S)$, and corresponding interpretations of observed structures are discussed.
We report the recent results on the measurement of charmonium-like and bottomonium-like resonances at Belle. The report includes the first observation of $Z_{b}(10610) \to B^{*}B$ and $Z_{b}(10650) \to B^{*}B^{*}$ and studies of bottomonium-like state using $\Upsilon(5S)$ and $\Upsilon(6S)$ data taken at Belle. We also report measurements of $B$ decays to charmonium and charmonium-like states.
Discoveries of exotic hadrons in the past years increased the interest from both theory and experiments. Using the LHCb Run-I data, several exotic hadrons are observed or searched for, and some precision measurements of the properties are performed. In this talk the most recent results are reported.
The D0 collaboration has recently reported evidence for a possible four-quark state named $X(5568)$ in the decay sequence $X(5568) \rightarrow B_s^0 \pi^{\pm}$, $B_s^0 \rightarrow J/\psi \phi$. Here we present a progress report on our search for the $X(5568)$ with semileptonic decays of the $B_s^0$ meson. We also report on a search for a strange pentaquark decaying to a $J/\psi \Lambda$ pair. The studies are based on $10.4~\rm{fb^{-1}}$ of $p \overline p $ collision data at $\sqrt{s}$ = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider.
Investigation of GPDs and TMDs represents the major goal of the COMPASS-II program. Together, GPDs and TMDs provide the most complete description of the
partonic structure of the nucleon.
GPDs are experimentally accessible via lepton-induced exclusive reactions, in
particular DVCS and DVMP. At COMPASS, these processes are investigated using a
160 GeV high intensity muon beam and a 2.5 m long liquid hydrogen target. In
order to optimize the selection of exclusive reactions at these energies, the target is surrounded by a new barrel-shaped time-of-flight system to detect the recoiling particles.
The pure DVCS cross-section and its $|t|$-dependence are extracted from the sum of cross-sections measured with opposite beam charges and polarizations.
From this measurement, the first estimate of the transverse size
of the nucleon in the uncharted $x_{Bj}$ domain from 0.02 to 0.20 will be given.
COMPASS is also capable of accessing several DVMP channels, from which different combinations of quark and gluon GPDs can be extracted. In this talk I will report on the first measurement of the exclusive $\pi^0$ cross section and its $|t|$-dependence in the same $x_{Bj}$ domain from 0.02 to 0.20.
Generalized Parton Distributions (GPDs) provide a comprehensive description of the partonic structure of the nucleon and contain a wealth of new information. In particular, they provide a description of the nucleon as an extended object, referred to as 3-dimensional nucleon tomography, and give an access to the orbital angular momentum of quarks.
In my talk I will focus on the GPD phenomenology. PARTONS project - the platform devoted to study GPDs, will be introduced and the first fits obtained by the PARTONS collaboration to the high precision Deeply Virtual Compton Scattering (DVCS) data collected at Jefferson Laboratory will be shown.
We propose to study the photoproduction of a photon and a rho meson with a large invariant mass as a new and efficient probe of Generalized Patron Distributions. A full feasibility study for such a process we be presented for the example of JLab@12GeV.
We report final results for L/T separated pi0 electroproduction cross sections off the proton, the neutron and the deuteron, measured in Hall A of Jefferson Lab. We found a large transverse response for both the proton and neutron cases, pointing to a possible dominance of higher-twist transversity GPD contributions. For the first time, a flavor decomposition of the u and d quark contributions to the cross section will be shown.
Generalized TMDs (GTMDs) of hadrons are the most general two-parton correlation functions. Upon certain projections several GTMDs reduce to generalized parton distributions and transverse momentum dependent parton distributions, respectively. Therefore they can be considered as partonic "mother functions". Moreover, two of the GTMDs play an important and unique role in the spin structure of hadrons.
By studying the exclusive double Drell-Yan process we show, for the first time, explicitly that quark GTMDs can in principle be measured. We will also address other processes that are directly sensitive to GTMDs.
We examine the constraints that future lepton colliders would impose on the top-quark effective field theory. All top-quark operators are simultaneously included and their effects are computed at next-to-leading order in QCD, in the MadGraph_aMC@NLO framework, including off-shell top effects.
The production of prompt isolated photons at hadron colliders provides a stringent test of perturbative QCD and can be used to probe the gluon density function of the proton.
The ATLAS collaboration has performed precise measurements of the inclusive production of isolated prompt photons at a center-of-mass energy of 13 TeV, differential in both rapidity and the photon transverse momentum. In addition, the integrated and differential cross sections for isolated photon pair production 8 TeV have been measured. The results are compared with state-of-the-art theory predictions at NLO in QCD and with predictions of several MC generators.
The LHC has recently precise measurements of the transverse momentum
of the $Z$ boson that provide a unique constraint on the structure of the
proton. Recent theoretical developments have allowed the calculation of these
process at next-to-next-to-leading order. In this talk theoretical fixed-order
predictions for this data are presented and their impact on the determination
of PDFs is described.
Measurements of the Drell-Yan production of W and Z/gamma bosons at the LHC provide a benchmark of our understanding of perturbative QCD and probe the proton structure in a unique way. The ATLAS collaboration has performed new high precision measurements at a center-of-mass energies of 7 and 13 TeV. The measurements are performed for W+, W- and Z/gamma bosons integrated and as a function of the boson or lepton rapidity and the Z/gamma* mass. Unprecedented precision is reached and strong constraints on Parton Distribution functions, in particular the strange density are found.
LHCb, while purpose built for b-physics, also functions as a general purpose forward detector, covering the pseudo-rapidity range 2.0 to 5.0. This has allowed performing several measurements concerning the production of W, Z and top. A selection of these results will be presented, highlighting the scope of the LHCb physics programme.
We consider the production of inclusive W bosons in variety of high-energy hadronic collisions: p-p, p-p$\overline{\rm p}$, p-Pb, and Pb-Pb. In particular, we focus on the resulting distributions of charged leptons from W decay that can be measured with relatively low backgrounds. The leading-order expressions within the collinearly factorized QCD indicate that the c.m. energy dependence at forward/backward rapidities should be well approximated by a simple power law. The interpretation of the scaling exponent is in the small-x behaviour of the quark distributions, which is largely driven by the parton evolution. An interesting consequence is the resulting, extremely simple scaling law for the lepton charge asymmetry which relates measurements in different collision systems. The expectations are contrasted with the existing data and a very good overall agreement is found. Finally, we propose precision observables to be measured at the LHC.
We study high-energy jet production in the multi-Regge limit making use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions.
Imposing infrared boundary conditions transforms the complex momentum w-plane cut present into an infinite series of positive Regge poles. In addition, a cut on the negative w line remains. We find a strong dependence of the asymptotic intercepts and collinear behaviour on the choice of the boundary conditions.
A simple factorized form of high energy QCD amplitudes with gluon quantum numbers in the cross channels and negative signature is known to be broken in the next-to-next-to-leading logarithmic approximation (NNLLA). It is argued that the violation is caused by contributions of three-Reggeon cuts. The consequent need to change the scheme of derivation of the BFKL equation in the NNLLA is discussed.
We discuss an application of formalism of Lipatov's effective action for the calculation of classical field of relativistic color charge, similarly to the done in CGC approach.
The equations of motion are solved in the LO and NLO approximation and the LO results are compared with the calculations performed in the CGC
framework. It is demonstrated that the CGC results for the classic field are reproduced in the calculations.
Additionally, the obtained gluon field solutions are considered as solution of classical equations of motion in the presence of external reggeon fields.
The possible applications of the NLO solution in the Lipatov's effective action and CGC frameworks are discussed as well.
The growth of the hadronic and nuclear scattering cross sections with energy is described by the linear BFKL
evolution equation. At very high energies, when the parton density becomes high, the hadronic cross section reaches the
unitarity limit, and the transition to high parton density is described by the non-linear BK and JIMWLK evolution
equations. These equations are currently the starting point of discussion for future experiments like the proposed Electron Ion Collider (EIC) or the Large Hadron electron Collider (LHeC) and also play an important role in current RHIC and LHC experiments involving nucleus-nucleus and proton-nucleus collisions. Most of the current phenomenology of high-energy and high-density QCD is based on the leading-order evolution equations with only running coupling corrections. I will present a systematic procedure to include higher-order corrections into the BFKL/BK/JIMWLK evolution equations and the corresponding scattering cross sections using the high-energy Operator Product Expansion in terms of composite Wilson line operators.
In the regime of low Bjorken x for DIS on a proton or nucleus target, one enters in the nonlinear regime of gluon saturation, where the gluons are better described as a strong coherent semi-classical field than as a collection of quasi on-shell partons. Hence, that regime lies outside the validity range of the collinear factorization, and is better described within the dipole factorization of DIS observables which allows to resum coherent multiple scattering on the target as well as the high-energy leading logarithms (LL).
So far, phenomenological studies have been performed successfully at LO in the dipole factorization, with high-energy LL resummation, using HERA data for inclusive DIS on a proton. However, in order to reach a decent precision for the theory, NLO corrections should be included, as well as high-energy NLL resummations. This is important not only to fully benefit from the great precision of HERA data, but also in prevision of future electron-proton and/or electron-nucleus colliders.
In this talk, I will present a full calculation of the (fixed order) NLO corrections to DIS structure functions on a dense target in the dipole factorization picture. In earlier studies, only one part of the NLO corrections has been calculated, the one corresponding to a quark-antiquark-gluon Fock state interacting with the target. By contrast, I will present the first direct calculation of the other part of NLO corrections, for which a quark-antiquark Fock state interacts with the target. I will also discuss issues related with the combination of the two pieces, with a consistent treatment of UV divergences.
Reference: G. Beuf, Phys.Rev. D94 (2016) no.5, 054016 (arXiv:1606.00777 [hep-ph])
Vector like quarks appear in many theories beyond the Standard Model as a way to cancel the mass divergence for the Higgs boson. The current status of the ATLAS searches for the production of vector like quarks will be reviewed for proton-proton collisions at 13 TeV. This presentation will address the analysis techniques, in particular the selection criteria, the background modeling and the related experimental uncertainties. The phenomenological implications of the obtained results will also be discussed.
Many models of physics beyond the Standard Model (SM) contain enhanced couplings to massive standard model particles like the W,Z,Higgs, and top. We present a review of non-SUSY based searches for new physics beyond the SM in final states containing these heavy particles, using proton-proton collision data collected with the CMS detector at the CERN LHC. The models probed can contain heavy gauge bosons, excited quarks, gravitons, and both chiral and vector-like top and bottom quark partners. We analyze a wide range of final states, from multi-leptonic to entirely hadronic, and many results use novel analysis techniques to identify and reconstruct highly boosted final states that are created in these topologies. These techniques provide increased sensitivity to new high-mass particles over traditional search methods.
Studying how ATLAS and CMS searches for supersymmetry in the t tbar + MET final state constrain scenarios with a fermionic top partner and a dark matter candidate, we show that the efficiencies of the considered searches are quite similar for scalar and fermionic top partners. Therefore, in general, efficiency maps for stop–neutralino simplified models can also be applied to fermionic top-partner models, provided the narrow width approximation holds in the latter.
This motivates the exploration of finite width effects in the production and decay of extra heavy quarks at the LHC, this dynamics being normally ignored in standard experimental searches. For this reason we assess the regions of validity of current approaches and study the impact of the Dark Matter candidate spin on the exclusion.
Many theories beyond the standard model predict new phenomena which decay to leptons and jets. Searches for new physics models with these signatures are performed using the ATLAS experiment at the LHC. The results reported here use the pp collision data sample collected in 2015 and 2016 by the ATLAS detector at the LHC with a centre-of-mass energy of 13 TeV.
Many physics scenarios beyond the standard model predict the existence of new particles decaying to dilepton, multilepton, and lepton+MET final states. This talk presents searches for BSM physics in these three final states at CMS, focusing on the recent results obtained using data collected at the LHC in 2016.
A wide program of studies of heavy flavour production in at LHC is performed with the ATLAS detector, including charm and beauty hadrons, quarkonia production in both sectors, and associated production $J/\psi + W$, $J/\psi + Z$ and, most recently, $J/\psi+ J/\psi$, which is the subject of this presentation.
The study is based on data collected at 8 TeV. The differential cross-section is measured as a function of the transverse momentum of the lower-$p_{\mathrm{T}}$ $J/\psi$ meson,
the di-$J/\psi$ $p_{\mathrm{T}}$ and mass, the difference in rapidity between the two $J/\psi$ mesons, and the azimuthal angle between the two $J/\psi$ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two $J/\psi$ mesons. The effective cross-section of double parton scattering is measured to be $\sigma_{\mathrm{eff}} =6.3 \pm 1.6(\mathrm{stat}) \pm 1.0(\mathrm{syst}) \pm 0.1(\mathrm{BF})\pm0.1(\mathrm{lumi})\,\mathrm{mb}$. The total and double parton scattering cross-sections are compared with predictions.
In this talk, I will review how quarkonia and their associated production -despite the debates regarding their production mechanisms- can provide us with useful information on double parton scatterings, on gluon TMDs (both in polarised and unpolarised protons) and on the (nuclear) gluon PDFs.
For that, I will report on recent studies of the production of quarkonium pairs, quarkonium + vector bosons and quarkonium+ heavy-flavour at LHC, Tevatron and AFTER@LHC. I will also discuss a new tool which we developed to account for the effect of the nuclear PDFs is a simple manner.
Heavy flavor production is a sensitive probe of all stages in the evolution of a heavy ion collision system. The characterization of the relative weights of the corresponding mechanisms (like energy loss or suppression by collisions with initial partons or comovers) requires a detailed description of the production, from $p$+$p$ and $p$+$A$ to $A$+$A$ collisions. Heavy quarkonia could also be direct probes of quark deconfinement in $A$+$A$ collisions.
The unique versatility and increasing performance of the BNL/RHIC collider has provided several beam and target combinations at $\sqrt{s}=200$ GeV to study heavy flavor production and modification. Also, improvements of the PHENIX experiment allow deeper study than has been previously published.
This talk aims at presenting the most recent PHENIX results on $J/\psi$, $\psi$' and open charm and beauty productions at $\sqrt{s}=200$ GeV in several collision systems and focus on the additional degrees of freedom in $p$+$A$ and $A$+$A$ collisions have compared to $p$+$p$ collisions.
Beyond the study of the hot and dense matter created in heavy-ion collisions, the ALICE experiment at the LHC has a unique potential to study proton-proton collisions with the goal to probe the Quantum ChromoDynamics (QCD). ALICE is particularly well suited for the reconstruction of low transverse momentum particles and in this way to measure the bulk of the production cross section of hadrons. In particular, quarkonia are very interesting because their production mechanisms are governed by both perturbative and non-perturbative QCD. This is why quarkonia represent a unique QCD laboratory. Several theoretical approaches (CEM, CSM, NRQCD) fail in describing simultaneously the differential cross section and polarization state. In ALICE, quarkonia are reconstructed via their dilepton decay channel in a large rapidity range and down to zero transverse momentum. An overview of quarkonium production results from ALICE will be presented and compared to other results from the LHC and from lower energy experiments. Finally, a critical comparison to theoretical predictions will be discussed.
Study of heavy quarkonium production cross-sections in $pp$ collisions provide important tests to our understanding of strong interactions. The LHCb experiment can contribute with results in unique kinematic range, low transverse momentum and large rapidity. In this talk recent results of heavy quarkonium production with the LHC Run 2 data will be presented.
During the past decade, the experiments of the RHIC spin program have provided critical insight into the spin structure of the nucleon, in particular, shedding light on the roles played by gluon and sea-quark helicity. In the forthcoming RHIC run, attention will be devoted to transverse-spin phenomena. Over the last decade, theoretical and experimental engagement of this oft-challenging subject has unlocked tantalizing opportunities for new insight into nucleon structure, e.g. with higher dimensions in partonic momentum space. The STAR experiment continues this exploration through an array of measurements from high-energy polarized-proton collisions. Among these studies are the production of weak bosons, azimuthal distributions of hadrons within jets, dihadron correlations, and particle production at large pseudorapidity. Recent breakthroughs may illuminate further longstanding questions: Do factorization and universality extend to the transverse-momentum-dependent (TMD) picture in proton-proton collisions? How do TMD functions evolve with changing kinematics? Beyond existing probes, future measurements will enable even wider frontiers in understanding QCD and nucleon structure.
Overview of transverse spin physics in the PHENIX experiment
We would like to present an overview of recent results from the PHENIX collaboration on spin physics using a transversely polarized proton beam. Several experiments have been conducted at RHIC in the past decade using such beam polarization in proton-proton collisions. Recently, polarized proton-ion collisions have also been studied.
Important recent transverse spin measurements in PHENIX include the transverse spin asymmetry in light meson production (π°, η), where a non-zero asymmetry can be interpreted as an initial state interaction (related to the Sivers effect) or a final state correlation (partially related to the Collins effect). Transverse spin asymmetries have also been measured for muons from heavy flavored hadrons and J/Ψ, and are related to the gluon Sivers function. Some of these asymmetries have also been measured in proton-ion collision allowing the study of nuclear dependence. Unexpected large asymmetries have been found and will be discussed.
Finally, the status of the Drell-Yan transverse spin asymmetry analysis will be presented. The latter aims at measuring the Sivers function, and compare it to semi-inclusive measurements. It is a unique check of the universality of Transverse Momentum Distributions and will improve our understanding of initial/final state effects in spacelike versus timelike reactions.
Due to the non-Abelian nature of QCD, there is a prediction that quarks can become correlated across colliding protons in hadron production processes sensitive to nonperturbative transverse momentum effects. Measuring the evolution of nonperturbative transverse momentum widths as a function of the hard interaction scale can help distinguish these effects from other possibilities. Collins-Soper-Sterman evolution comes directly from the proof of transverse-momentum-dependent (TMD) factorization for processes such as Drell-Yan, semi-inclusive deep-inelastic scattering, and e+e- annihilation and predicts nonperturbative momentum widths to increase with hard scale. Experimental results from proton-proton and proton-nucleus collisions, in which TMD factorization is predicted to be broken, will be presented. The results show that these widths decrease with hard scale, suggesting possible TMD factorization breaking and color entanglement of partons across colliding protons.
The sea quark contribution to nucleon spin is an important piece for a complete understanding of the nucleon spin structure. The production of $W$-bosons in longitudinally polarized $p+p$ collisions at RHIC provides a unique probe for the sea quark polarization, through the parity-violating single-spin asymmetry, $A_L$. At the STAR experiment, the leptonic decay channel $W\rightarrow e\nu$ can be effectively determined with the Electromagnetic Calorimeters and Time Projection Chamber at mid-rapidity. The previous STAR measurements of $A_L$ for $W$ boson from datasets taken in 2011 and 2012, have provided significant constraints on the helicity distribution functions of $\bar{u}$ and $\bar{d}$ quarks. In 2013 the STAR experiment collected an integrated luminosity of $\sim300\,\mathrm{pb^{-1}}$ at $\sqrt{s} = 510\,\mathrm{GeV}$ with an average beam polarization of $\sim56\%$, which is more than three times larger than the total integrated luminosity of previous years. The new preliminary results of $W$-bosons $A_L$ from 2013 data sample will be presented.
The production of jets from polarized p+p collisions at STAR is dominated by quark-gluon and gluon-gluon scattering. The di-jet double spin asymmetry ($A_{LL}$) is sensitive to the polarized gluon distribution ($\Delta G$). Di-jets are also advantageous because the parton momentum fraction, x, of initial partons may be reconstructed to first order from the final state measurements. Both jet (PRL 115,092002) and di-jet (arXiv:1610.06616) $A_{LL}$ measurements at $\sqrt{s}$ = 200 GeV have helped to constrain $\Delta G$ in the range $0.05 < x < 0.3$. In 2012, data were collected at $\sqrt{s}$ = 510 GeV in order to probe lower values of x, these data are consistent with the $\sqrt{s}$ = 200 GeV results in the overlapping $x_T$ region. Jet and di-jet preliminary $A_{LL}$ results have been released and will soon be incorporated into theoretical fits. In 2013, high luminosity data, with an estimated 250 pb$^{-1}$ of integrated luminosity were collected at $\sqrt{s}$ = 510 GeV. These data have a figure of merit $\approx$3 times that of the 2012 data. An update on the di-jet $A_{LL}$ measurement will be presented using polarized p+p data collected at STAR during 2013.
We present the transverse single spin asymmetries $A_N$ for very forward neutrons measured by the PHENIX zero-degree calorimeters (ZDCs) in high-energy polarized proton-nucleus (p-A) collisions at RHIC. First-ever p-A data taken in the RHIC-2015 run exhibit positive and remarkably large $A_N\sim0.18$ only in p-Au collisions whereas nearly zero $A_N$ in p-Al collisions. Comparisons of these new results with $A_N=-0.05$ from the previous PHENIX-ZDC measurement in p-p collisions raised the following question: what mechanisms do produce such a large $A_N$ in only p-Au collisions and smaller or close to zero $A_N$ in other collisions? One attempt is a single-Reggeon exchange model considering the interference of pion (spin flip) and $a_1$-Reggeon (spin nonflip). Single-Reggeon exchange well explains $A_N$ in p-p collisions and can be extended to p-A collisions by taking into account strong nuclear absorption correction as well as nuclear breakup. However, the predicted $A_N$ by the extended single-Reggeon exchange model is far smaller than the PHENIX data in p-Au collisions. In this talk, we will discuss an alternative and rather unknown mechanism: ultra-peripheral p-A collisions (UPCs, also known as Primakoff effects). UPCs lead to very large $A_N$ of about 0.35 and have cross sections proportional to $Z^2$ of the nuclei. UPCs contribute to inclusively measured $A_N$ modestly in p-Al collisions and significantly in p-Au collisions. To discuss quantitatively, we will show that the Monte Carlo simulations incorporating both the Reggeon exchange and UPCs, where virtual photon--polarized proton interactions follow the MAID 2007 isobar model, successfully describe the PHENIX data in p-Al and p-Au collisions simultaneously.
A detector for the proposed the Jefferson Lab realization for the Electron-Ion Collider is being developed. Current status will be described.
The 2015 US Nuclear Physics Long Range Plan called for a state-of-the-art jet and upsilon detector at RHIC, called sPHENIX, to study the microscopic nature of the Quark Gluon Plasma in Heavy Ion collisions, complementing similar studies at the CERN LHC. The sPHENIX detector will provide precision vertexing, tracking and full calorimetry over pseudorapidity |$\eta$| < 1.1 and full azimuth at the full RHIC collision rate, delivering unprecedented data sets for jet and upsilon measurements at RHIC. In the same Long Range Plan, an Electron-Ion Collider was recommended as the highest priority for future construction. The EIC will allow for precision measurements of the partonic and spin structure of hadronic and nuclear matter using e+p and e+A collisions. In this talk I will present an overview of the sPHENIX detector design, expected construction and running schedule, and planned physics program. I will highlight the possibility to complement sPHENIX with additional forward instrumentation for spin polarized p+p/A physics and the potential to evolve sPHENIX into a spin polarized e+p/A detector at a future EIC.
The large data samples at the High-Luminosity LHC will enable precise measurements of the Higgs boson and other Standard Model particles, as well as searches for new phenomena such as supersymmetry and extra dimensions. To cope with the experimental challenges presented by the HL-LHC such as large radiation doses and high pileup, the current Inner Detector will be replaced with a new all-silicon Inner Tracker for the Phase II upgrade of the ATLAS detector. The current tracking performance of two candidate Inner Tracker layouts with an increased tracking acceptance (compared to the current Inner Detector) of |η|<4.0, employing either an ‘Extended’ or ‘Inclined’ Pixel barrel, is evaluated. The forward coverage will enable track-based rejection of forward pileup jets, which is particularly beneficial for studies of vector boson scattering and Higgs boson production through vector boson fusion, amongst other advantages.
The Tile Calorimeter (TileCal) is the central hadronic calorimeter of the ATLAS experiment at the LHC. Jointly with the other calorimeters it is designed for reconstruction of hadrons, jets, tau-particles and missing transverse energy. It also assists in muon identification. A summary of the upgrades and performance results for TileCal using pp collisions from the LHC Run II at 13 TeV will be presented. For the high luminosity era a major upgrade of the TileCal electronics is planned, and the ongoing developments for on- and off-detector systems, together with expected performance characteristics and recent beam tests of prototypes, will be described.
We present the impact of recent V+jets measurements performed by the CMS collaboration on the constraints of PDFs.
Realizing the precision physics paradigm at the LHC requires the calculation of hard-scattering cross-sections which include perturbative QCD corrections up to (N)NNLO and electroweak corrections up to NLO. For consistency, parton distribution functions (PDFs) need to be provided with matching accuracy, which in the case of QED effects involves introducing the photon parton distribution of the proton, $x\gamma(x;Q)$. In this work, a novel determination of the photon PDF from fits to the recent ATLAS measurements of high-mass Drell-Yan production at $\sqrt{s}$ = 8 TeV has been presented. The analysis is performed using the xFitter framework which involves improvements both in the APFEL program, to account for NLO QED effects, and in the aMCfast interface to account for the photon-initiated contributions in the EW calculations within MadGraph5_aMC@NLO. The results of this work have been compared with other recent QED fits and determinations, finding in particular good agreement with the LUXqed and the HKR calculations within PDF uncertainties, in the kinematical range where the ATLAS DY measurement has sensitivity to $x\gamma(x;Q)$.
Novel tagged beam and target techniques are being developed to create effective neutron, pion, and other targets from nucleon and nuclear targets and beams. The effective meson targets in particular open the opportunity to uniquely probe the structure and composition of mesons and the nucleon sea. This talk will discuss some results from the 6 GeV era at Jefferson Lab, approved and possible tagged deep inelastic scattering experiments at Jefferson Lab in the 12 GeV era, and look forward also to potential tagged experiments at the Electron Ion Collider.
Neutrino-nucleus charged-current deep inelastic scattering (DIS) provides a complementary probe to charged lepton-nucleus DIS in the study of nuclear and hadronic structure. The MINERvA experiment is a dedicated neutrino scattering experiment located on the NuMI beamline in Fermilab. With multiple nuclear targets of Pb, Fe, CH, and C in the same beam, MINERvA has the capability to add to the world knowledge of DIS that still contains poorly understood nuclear effects. The recent change of the NuMI beam line to the Medium Energy configuration has increased both the intensity and average neutrino energy thereby greatly improving the projected sensitivities for nuclear and hadronic structure analyses utilizing MINERvA's multiple nuclear targets. The measurements of nuclear cross section ratios C, Fe, Pb to CH using the MINERvA low energy data set will be discussed as well as the current DIS analysis with the medium energy data set
Studies of correlated hadron production are an important source of information about the early stages of hadron formation, not yet understood from first principles. Although experimental high energy physics employs several semi–classical models of hadronization which describe the formation of jets with remarkable accuracy, correlation phenomena are more elusive. In this presentation, we will discuss Bose-Einstein correlations measured with the ATLAS detector and provide a unique opportunity for detailed understanding of the space-time geometry of the hadronization region. If available, an analysis of the momentum difference between charged hadrons in high–energy proton–proton collisions will be also presented, which is performed in order to study coherent particle production. This allows the investigation of observables sensitive to the predictions of the quantized string model.
We address the general features of event-by-event fluctuations of the multiplicity of gluons produced in the scattering of a dilute hadron off a large nucleus at high energy in the fragmentation region of the dilute hadron. We relate these fluctuations to the stochasticity of the number of quanta contained in the hadron at the time of the interaction. For simplicity, we address the ideal case in which the hadron is an onium, and investigate different kinematical regimes in rapidity and onium size. We show that at large rapidity, the multiplicity distribution exhibits an exponential tail in the large-multiplicity region, which is qualitatively consistent with the proton-nucleus data. But interestingly enough, the exponential shape is determined by confinement. We shall also present new numerical checks of our analytical calculations.
The explanation of the ridge observed in pp and pA collisions at the Large Hadron Collider constitutes one of open questions in our understanding of high-energy hadronic collisions. Apart from final-state hydrodynamic models, correlations between gluons in the wave function of the incoming hadrons, computed in the framework of the Color Glass Condensate, offer an alternative rationale to explain such phenomenon. A natural question is then what happens to quarks. Here we consider, for the first time, correlations between produced quarks in pA collisions in the light-cone wave function approach to the CGC. We find a quark-quark ridge that shows a dip at $\Delta\eta\sim 2$ relative to the gluon-gluon ridge. The origin of this dip is the short range (in rapidity) Pauli blocking experienced by quarks in the wave function of the incoming projectile. We observe that these correlations, present in the initial state, survive the scattering process. We discuss possibilities for observing such correlations e.g. in open charm-open charm correlations at the LHC.
Reference: T. Altinoluk, N. Armesto, G. Beuf, A. Kovner and M. Lublinsky, arXiv:1610.03020 [hep-ph]
The inclusive production of a pair of hadrons (a “dihadron” system), having high transverse momenta and separated by a large interval of rapidity, is investigated. This process has much in common with the widely discussed Mueller-Navelet jet production and can be also used to access the BFKL dynamics at proton colliders. The first full NLA BFKL analysis for cross sections and azimuthal angle correlations for dihadrons produced in the LHC kinematic ranges is presented. It is made use of the Brodsky-Lapage-Mackenzie (BLM) optimization method to set the values of the renormalization scale and study the effect of choosing different values for the factorization scale. The uncertainty coming from the use of different PDF and FF parametrizations is also investigated.
We present the effective weak angle measurements from the CDF and D0¬ experiments at Fermilab. We combine the most precise published results based on the forward-backward asymmetry of $p\bar{p}\rightarrow Z/\gamma^{*} \rightarrow e^+ e^-/\mu^+\mu^- + X$ events in the full Run II data set corresponding to up to $10 fb^{-1}$ of luminosity. We use the extracted values of $\sin^2\theta_{eff}^{lept}$ with an on-shell renormalization scheme in a standard model context to make indirect measurements of $\sin^2\theta_{W}$ and $m_{W}$. We also review direct measurements of $m_{W}$ at the Tevatron and discuss the relative precision of the direct and indirect measurements.
A precise measurement of the mass of the W boson mass represents an important milestone to test the overall consistency of the Standard Model. Since the discovery of a Higgs Boson, the the W boson mass is predicted to 7 MeV precision, while the world average of all measurements is 15 MeV, making the improved measurement an important goal.
The ATLAS experiment at the LHC represents an ideal laboratory for such a precise measurement. Large samples of many millions of leptonic decays of W and Z bosons were collected with efficient single lepton triggers in the 7 TeV data set corresponding to an integrated luminosity of 4.6/fb. With these samples the detector and physics modelling has been studied in great detail to enable a systematic uncertainty on the measurement that approaches the statistical power of the data of 7 MeV per decay channel as far as possible.
We attempt to estimate the top-quark mass extraction uncertainty due to Monte Carlo modeling of top-pair production and its leptonic decay. Using three different NLO+PS generators based on the POWHEG method implementing an increasingly precise treatment of $t\bar{t}$ production and decay, including hvq and bb4l, and two different PS implementations we obtain predictions for various kinematic distributions suitable for extraction of the top mass proposed in the literature. Assuming that one of the generators reproduces the data fully, we estimate the shift in the extracted top mass using the other generators. We find that the mass shifts are comparable to the current experimental uncertainty on the top mass extraction.
We review the recent developments of the Loop-Tree Duality method, focussing our discussion on the first numerical implementation and its use in the direct numerical computation of multi-leg Feynman integrals. Non-trivial examples are presented.
The 2015 nuclear physics long-range plan endorsed the realization of an electron-ion collider (EIC) as the next large construction project after the completion of FRIB.
With its high luminosity ( $> 10^{33} cm^{-2}s^{-1}$), wide kinematic reach in center-of-mass-energy (45 GeV to 145 GeV) and high lepton and proton beam polarization, the EIC provides an unprecedented opportunity to reach new frontiers in our understanding of the spin and dynamic structure of nuclei.
Despite of the success of the HERA collider in investigating the structure of a single nucleon, the partonic structure of nuclei at moderate-to-small Bjorken's $x$ still remain elusive.
This talk will present the evaluated impact of an EIC in extracting the nuclear structure-functions from measurements of the reduced cross sections in deep inelastic scattering, including also the case of measuring heavy quark production events. The potential constraints offered by the EIC data in extracting the nuclear parton distribution functions will be discussed.
We calculate the leading order in $α_s$ QCD amplitude for exclusive neutrino and antineutrino production of a D pseudoscalar charmed meson on an unpolarized nucleon. We work in the framework of the collinear QCD approach where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We include both $O(m_c)$ terms in the coefficient functions
and $O(M_D)$ mass term contributions in the heavy meson distribution amplitudes. We emphasize the sensitivity of specific observables on the transversity quark GPDs.
Wigner distributions give a three dimensional picture of the quarks and gluons in a nucleon, and are related to the generalzed transverse momentum dependent parton distributions (GTMDs). These also give the orbital angular momentum and the spin-orbit correlations of the quarks and gluons. We calculate the Wigner distributions and GTMDs for a simple spin 1/2 composite state, namely a quark dressed with a gluon, for different target and quark polarization including transverse polarization. We also discuss the gluon Wigner distributions in this model for different polarizations.
Hadron tomography can be investigated by three-dimensional structure functions
such as generalized parton distributions (GPDs),
transverse-momentum-dependent parton distribution (TMDs),
and generalized distribution amplitudes (GDAs).
Here, we extract the GDAs, which are $s$-$t$ crossed quantities of
the GPDs, from cross-section measurements of
hadron-pair production process $\gamma \gamma^* \rightarrow h \bar h$.
The GPDs are expressed by a number of parameters and they are determined
from the hadron-pair production data. We discuss the dependence
on parton-momentum fraction $z$ in the GDAs and also time-like form factor.
Our studies should be valuable for probing the three-dimensional
structure of hadrons, especially for applications to
exotic hadron candidates which cannot be used as fixed targets
for GPD and TMD measurements.
Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is the exclusive pion-induced Drell-Yan process, $\pi^- p \to \mu^+ \mu^- n$. We discuss recent theoretical advances on describing this process in terms of QCD factorization as the partonic subprocess convoluted with the nucleon GPDs and the pion distribution amplitudes [1-3]. Based on this result, we mention the feasibility study for measuring the exclusive pion-induced Drell-Yan process via a spectrometer at the High Momentum Beamline being constructed at J-PARC [3].
We also point out that there could be the corrections beyond the QCD factorization framework due to ``soft mechanisms’’ caused by the treatment of the pion pole contribution arising in the relevant GPDs in the ERBL region, the parton transverse momentum to regularize the endpoint singularities, the so-called soft-overlap mechanism, etc. Those soft mechanisms could give important contributions at J-PARC kinematics [2], and we present a new estimate of the soft mechanisms making use of dispersion relations and quark-hadron duality [4]. We note that our approach allows us to calculate the soft mechanisms as well as the factorizable mechanisms using the GPDs; thus, realization of the measurement of the exclusive pion-induced Drell-Yan process at J-PARC will provide a new test of QCD descriptions of a novel class of hard exclusive reactions. It will also offer the possibility of experimentally accessing nucleon GPDs at large timelike virtuality.
This talk is based on my recent publication [3] in collaboration with several theorists and experimentalists, and my new result [4] in preparation.
References:
[1] E.R. Berger, M. Diehl, and B. Pire, Phys. Lett. B523 (2001) 265.
[2] S. V. Goloskokov and P. Kroll, Phys.Lett. B748 (2015) 323.
[3] T. Sawada, W. C. Chang, S. Kumano, J. C. Peng, S. Sawada and K. Tanaka, Phys.
Rev. D 93, 114034 (2016) [arXiv:1605.00364 [nucl-ex]].
[4] K. Tanaka, in preparation.
We have computed the fourth-order nf2 contributions to all three non-singlet quark–quark splitting functions and their four nf3 flavour-singlet counterparts for the evolution of the parton distributions of hadrons in perturbative QCD with nf effectively massless quark flavours. In this talk we give an overview of the method used to reconstruct the analytic form of these functions from their Mellin moments, computed by the recently-developed FORCER package.
The combined inclusive DIS data from HERA are described
with DGLAP fits at NLO and NNLO, combined with a model
for twist 4 corrections originating from the GBW saturation
model. Besides the higher twist effects, modifications
are introduced at small x to the input functions for the
twist 2 parton distribution functions that are inspired by
findings of QCD at high parton densities. It is shown that
both inclusion of the higher twist effects and the input
modification of the DGLAP fit lead to significant improvement
of the fit quality below Q^2 = 5 GeV^2. With the best fit
employing the NNLO DGLAP evolution combined with higher twist
corrections, a good desription of DIS data is obtained down
to Q^2 = 1 GeV^2. The impact of higher twist corrections on
the parton desity functions is presented.
We present CT14 Monte-Carlo replica PDFs that reproduce important properties of CT14 Hessian PDFs: the asymmetry of CT14 uncertainties and positivity of individual parton distributions. The ensembles of CT14 Monte-Carlo replicas constructed this way at NNLO and NLO are suitable for various collider applications, such as cross section reweighting.
We present the xFitter project (former HERAFitter) which provides a unique open-source software framework for the determination of the proton's PDFs and for the interpretation of the physics analyses in the context of Quantum Chromodynamics.
We highlight the new xFitter software release which includes state-of-the-art theoretical developments with direct applications for the various PDF sensitivity studies.
Current (and future) collider energies, as well as high-energy astroparticle interactions in the atmosphere, allow to probe the proton at very small values of the parton momentum fraction x. At small x, both perturbative partonic coefficients and DGLAP splitting functions are affected by a logarithmic growth, which eventually spoils the perturbativity of the alphas expansion. These small-x logarithms can be resummed to all orders in alphas, thanks to techniques developed more than 10 years ago. Today, we resurrected these techniques and developed a numerical code, named HELL, which provides resummed splitting functions and coefficient functions. Within the framework of the NNPDF methodology, the code HELL allows for the determination of new PDFs, reliable at small x, necessary for the description of highly energetic processes involving protons.
The forward Drell-Yan process is analysed assuming dominance of the
quark-gluon partonic channel in the asymmetric kinematic configuration
in which x of the gluon is very small. The small x logarithms in the
gluon evolution are resummend using the BFKL formalism. Effects of
the resummation are determined in all the Drell-Yan structure functions.
In particular the impact of the gluon transverse momentum on the
Lam-Tung relation breaking is investigated.