Large-x Region Research Articles

Simultaneous reweighting of Transverse Momentum Dependent distributions

The Bayesian reweighting procedure is extended to the case of multiple independent extractions of transverse momentum dependent parton distributions (TMDs). By exploiting the data on transverse single spin asymmetries, AN, for inclusive pion production in polarized proton-proton collisions measured at RHIC, we perform a simultaneous reweighting of the quark Sivers, transversity and Collins TMD functions extracted from semi-inclusive deep inelastic scattering (SIDIS) and e+e− annihilation into hadron pairs. The impact of the implementation of the Soffer bound, as well as the differences between older and newer AN data, are investigated. The agreement with AN data at large-xF values, a kinematical region complementary to those explored in SIDIS measurements, is enhanced, improving the knowledge of the polarized quark TMDs in the large-x region.

Perturbative QCD contribution to transverse single spin asymmetries in the Drell-Yan process and SIDIS

In a previous publication [Benić , ], we have computed the perturbative QCD contribution to transverse single spin asymmetries (SSAs) in semi-inclusive deep inelastic scattering (SIDIS) involving the gT(x) distribution. In this paper, we first present a more efficient derivation of the asymmetries which is applicable to both transverse and longitudinal SSAs and correct some inconsistencies in our previous calculation. We then adapt the method to compute transverse SSAs in the Drell-Yan process proportional to gT(x) and its gluonic counterpart and discuss the crossing symmetry between the results for SIDIS and the Drell-Yan process. Finally, we present numerical results for various asymmetries measurable at the EIC, RHIC, COMPASS, and Fermilab (SpinQuest), including also part of the genuine twist-three corrections to gT(x) from a recent global analysis. We find that the asymmetries can reach percent-level magnitude, if the kinematics predominantly probes the large-x (valence) region of the polarized proton, but remain at subpercent levels otherwise. Published by the American Physical Society 2024

Gluon distribution and mass decomposition of the pion and kaon

We present the gluon distribution functions of the pion and kaon in small-x and large-x regions, and compare them with the results obtained from lattice QCD and continuum Schwinger function methods. Whether in the small-x region or the large-x region, our gluon distribution of the pion is consistent with the results of lattice QCD and continuum Schwinger function methods. We also calculate the first four moments of gluon distributions of the pion and kaon at different Q2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q^{2}$$\\end{document} scales. In addition, we present the mass decomposition of the pion and kaon with the dynamical parton distribution functions calculated by the DGLAP equation with parton–parton recombination corrections. The mass structures of the pion and kaon are completely different from that of the proton.

Parton distributions in the SMEFT from high-energy Drell-Yan tails

The high-energy tails of charged- and neutral-current Drell-Yan processes provide important constraints on the light quark and anti-quark parton distribution functions (PDFs) in the large-x region. At the same time, short-distance new physics effects such as those encoded by the Standard Model Effective Field Theory (SMEFT) would induce smooth distortions to the same high-energy Drell-Yan tails. In this work, we assess for the first time the interplay between PDFs and EFT effects for high-mass Drell-Yan processes at the LHC and quantify the impact that the consistent joint determination of PDFs and Wilson coefficients has on the bounds derived for the latter. We consider two well-motivated new physics scenarios: 1) electroweak oblique corrections ( hat{W},hat{Y} ) and 2) four-fermion interactions potentially related to the LHCb anomalies in R(K(*)). We account for available Drell-Yan data, both from unfolded cross sections and from searches, and carry out dedicated projections for the High-Luminosity LHC. Our main finding is that, while the interplay between PDFs and EFT effects remains moderate for the current dataset, it will become a significant challenge for EFT analyses at the HL-LHC.

Impact of new neutrino deep inelastic scattering and Drell-Yan data on large-xparton distributions

New data sets have recently become available for neutrino and antineutrino deep inelastic scattering on nuclear targets and for inclusive dimuon production in pp and pd interactions. These data sets are sensitive to different combinations of parton distribution functions in the large-x region and, therefore, provide different constraints when incorporated into global parton distribution function fits. We compare and contrast the effects of these new data on parton distribution fits, with special emphasis on the effects at large x. The effects of the use of nuclear targets in the neutrino and antineutrino data sets are also investigated.

Unintegrated gluon in the photon and heavy quark production

The unintegrated gluon density in the photon is determined, using the Kimber-Martin-Ryskin prescription . In addition, a model of the unintegrated gluon is proposed, based on the saturation model extended to the large-x region. These gluon densities are applied to obtain cross sections for charm and bottom production in gamma-p and gamma-gamma collisions using the k_t factorization approach. We investigate both direct and resolved photon contributions and make comparison with the results from the collinear approach and the experimental data. An enhancement of the cross section due to inclusion of non-zero transverse momenta of the gluons is found. The charm production cross section is consistent with the data. The data exceed our conservative estimate for bottom production in gamma-p collisions, but theoretical uncertainties are too large to claim a significant inconsistency. A substantial discrepancy between theory and the experiment is found for gamma gamma -> b bbar X, not being cured by the k_t factorization approach.

Leading and higher twists in the proton polarized structure functiong1pat large Bjorkenx

A phenomenological parametrization of the proton polarized structure function ${g}_{1}^{p}{(x,Q}^{2})$ is developed for $x\ensuremath{\gtrsim}0.02$ using deep inelastic data up to $\ensuremath{\sim}50 (\mathrm{GeV}{/c)}^{2}$ as well as available experimental results on both photo- and electroproduction of proton resonances. According to the new parametrization the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a zero-crossing point at ${Q}^{2}=0.16\ifmmode\pm\else\textpm\fi{}0.04 (\mathrm{GeV}{/c)}^{2}.$ Then, low-order polarized Nachtmann moments are estimated and their ${Q}^{2}$ behavior is investigated in terms of leading and higher twists for ${Q}^{2}\ensuremath{\gtrsim}1 (\mathrm{GeV}{/c)}^{2}.$ The leading twist is treated at NLO in the strong coupling constant and the effects of higher orders of the perturbative series are estimated using soft-gluon resummation techniques. In the case of the first moment, higher-twist effects are found to be quite small for ${Q}^{2}\ensuremath{\gtrsim}1 (\mathrm{GeV}{/c)}^{2},$ and the singlet axial charge has been determined to be ${a}_{0}[10 (\mathrm{GeV}{/c)}^{2}]=0.16\ifmmode\pm\else\textpm\fi{}0.09.$ In the case of higher order moments, which are sensitive to the large-x region, higher-twist effects are significantly reduced by the introduction of soft gluon contributions, but they are still relevant at ${Q}^{2}\ensuremath{\sim}$ few $(\mathrm{GeV}{/c)}^{2}$ at variance with the case of the unpolarized transverse structure function of the proton. Our finding suggests that spin-dependent correlations among partons may have more impact than spin-independent ones. As a by-product, it is also shown that the Bloom-Gilman local duality is strongly violated in the region of polarized electroproduction of the $\ensuremath{\Delta}(1232)$ resonance.

Deep inelastic lepton-hadron scattering as a test of perturbative QCD

Exploration of the small x kinematic region by the HERA experiments led to a revival of some models which existed before the advent of Quantum Chromo Dynamics (QCD) as the theory of the strong interactions. Predictions of these models for the deep inelastic structure functions are compared with those given by QCD. Future experiments will concentrate on the large x-region and we will discuss some issues which are important for the test of QCD. In particular we emphasize the next-to-next-to-leading (NNLO) order analysis of the structure functions and the determination of the strong coupling constant α s . We also make some critical remarks about the relevance of so called large corrections in the small and large x-region.

Sudakov resummation for prompt-photon production in hadron collisions

We present the explicit expressions for the resummation of large-x Sudakov effects in the transverse-energy distribution of prompt-photons produced in hadronic collisions, to next-to-leading logarithmic (NLL) accuracy. Fragmentation processes do not contribute to the Sudakov resummation at NLL level. In Mellin space, the resummed radiative factor factorizes in the product of independent radiators for the two initial and the one final coloured partons appearing in the Born process, times a simple factor describing the soft-gluon interferences between initial and final states. The formulae are given in terms of Mellin moments, and can be used for phenomenological applications using standard techniques for the inverse-Mellin transforms. The calculations presented in this work, when added to the existing works on DY and DIS production, complete the theoretical ground-work necessary to carry out global fits of parton densities with a uniform NLL accuracy in the large-x region.

Fermionic next-to-leading-order contributions to the longitudinal structure function in QCD.

The full analytic result of the quark contribution to F/sub L/(x,Q/sup 2/) up to next-to-leading order is presented. The phenomenological implications are discussed for the large-x region, where gluons are not supposed to be relevant but other effects, such as higher twist, have to be included.

Evidence for Large-xCorrections in Quantum Chromodynamics

We show there is evidence that a method of summing important logarithmic corrections which are significant in the large-x region leads to a superior description of deep-inelastic scattering data (analyzed using the evolution equations). Next-to-leading-order calculations can imitate the impact of this summation method, but at high x it appears that there are higher-order and higher-twist corrections which separate those approaches.