29 research outputs found
Massive neutral gauge boson production as a probe of nuclear modifications of parton distributions at the LHC
We analyze the role of nuclear modifications of parton distributions,
notably, the nuclear shadowing and antishadowing corrections, in production of
lepton pairs from decays of neutral electroweak gauge bosons in proton-lead and
lead-collisions at the LHC. Using the Collins-Soper-Sterman resummation
formalism that we extended to the case of nuclear parton distributions, we
observed a direct correlation between the predicted behavior of the transverse
momentum and rapidity distributions of the produced vector bosons and the
pattern of quark and gluon nuclear modifications. This makes Drell-Yan pair
production in and collisions at the LHC a useful tool for
constraining nuclear PDFs in the small- shadowing and moderate-
antishadowing regions.Comment: 33 pages, 17 figure
Effects of next-to-leading order DGLAP evolution on generalized parton distributions of the proton and deeply virtual Compton scattering at high energy
We studied the effects of NLO Q2 evolution of generalized parton distributions (GPDs) using the aligned-jet model for the singlet quark and gluon GPDs at an initial evolution scale. We found that the skewness ratio for quarks is a slow logarithmic function of Q2, reaching rS=1.5−2 at Q2=100 GeV2 and rg≈1 for gluons in a wide range of Q2. Using the resulting GPDs, we calculated the DVCS cross section on the proton in NLO pQCD and found that this model in conjunction with modern parameterizations of proton PDFs (CJ15 and CT14) provides a good description of the available H1 and ZEUS data in a wide kinematic range
Exclusive quarkonium photoproduction in + UPCs at the LHC in NLO pQCD
We present the first study of coherent exclusive quarkonium (,
) photoproduction in ultraperipheral nucleus-nucleus collisions
(UPCs) at the LHC in the framework of collinear factorization and
next-to-leading order (NLO) perturbative QCD (pQCD). We make NLO predictions
for the and rapidity distributions for lead (Pb) and oxygen
(O) beams, and quantify their dependence on the factorization/renormalization
scale, nuclear parton distribution functions (PDFs) and their uncertainties,
and on differences between nuclear PDFs and generalized parton distribution
functions (GPDs). We show that within the PDF-originating uncertainties our
approach provides a good description of the available photoproduction
data in Pb+Pb UPCs at the LHC but that the scale uncertainty is significant. We
demonstrate that at NLO pQCD the quark contributions are important in the
case but that gluons clearly dominate the cross sections.
We also study how the scale dependence could be tamed by considering O+O/Pb+Pb
ratios of the exclusive UPC cross sections, and how HERA and p+p/Pb
LHC data can help in obtaining better-controlled NLO predictions in the
case.Comment: 6 pages, 5 figures, contributed talk by K.J.E. at the 11th
International Conference on Hard and Electromagnetic Probes of High-Energy
Nuclear Collisions, Hard Probes 2023, 26-31 March 2023, Aschaffenburg,
German
Exclusive J/psi : photoproduction in ultraperipheral Pb plus Pb collisions at the CERN Large Hadron Collider calculated at next-to-leading order perturbative QCD
We present the first next-to-leading-order (NLO) perturbative QCD (pQCD) study of rapidity-differential cross sections of coherent exclusive photoproduction of J/psi mesons in heavy-ion ultraperipheral collisions (UPCs) at the CERN Large Hadron Collider (LHC), d sigma /dy(Pb + Pb -> Pb + J/psi + Pb). For this, we account for the photon-nucleon NLO cross sections at the forward limit, the t dependence using a standard nuclear form factor, and the photon fluxes of the colliding nuclei. Approximating the generalized parton distributions with their forward-limit parton distribution functions (PDFs), we quantify the NLO contributions in the cross sections, show that the real part of the amplitude and quark-PDF contributions must not be neglected, quantify the uncertainties arising from the scale choice and PDFs, and compare our results with ALICE, CMS, and LHCb J/psi photoproduction data in Pb + Pb UPCs, exclusive J/psi photoproduction data from HERA, and LHCb data in p + p. The scale dependence in d sigma /dy(Pb + Pb & RARR; Pb + J/psi + Pb) is significant, but we can find a scale choice that reproduces the Pb + Pb UPC data at both 2.76 and 5.02 TeV collision energies. This process has traditionally been suggested to be a direct probe of nuclear gluon distributions. We show that the situation changes rather dramatically from LO to NLO: the NLO cross sections reflect the nuclear effects of both gluons and quarks in a complicated manner, where the relative signs of the LO and NLO terms in the amplitude play a significant role.Peer reviewe
Nuclear parton distribution functions with uncertainties in a general mass variable flavor number scheme
In this article, we obtain a new set of nuclear Parton distribution functions (nuclear PDFs) at next-to-leading order and next-to-next-to-leading order accuracy in perturbative QCD. The common nuclear deep-inelastic scattering (DIS) data analyzed in our study are complemented by the available charged-current neutrino DIS data with nuclear targets and data from Drell-Yan cross-section measurements for several nuclear targets. In addition, the most recent DIS data from the Jefferson Lab CLAS and Hall C experiments are also added to our data sample. For these specific datasets, we consider the impact of target mass corrections and higher twist effects which are expected to be important in the region of large x and intermediate-to-low Q2. Our analysis is based on a publicly available open-source tool, APFEL, which has been modified to be applicable for our analysis of nuclear PDFs. Heavy-quark contributions to nuclear DIS are considered within the framework of the FONLL general-mass variable-flavor-number scheme. The most recent CT18 PDFs are used as baseline proton PDFs. The uncertainties of nuclear PDFs are determined using the standard Hessian approach. The results of our global QCD analysis are compared with existing nuclear PDF sets and with the fitted cross-sections, for which our set of nuclear PDFs provides a very good description
Study of Nondiagonal Parton Distribution Models
In this paper we examine predictions from different models of nondiagonal
parton distributions. This will be achieved by examining whether certain
predictions of relationships between diagonal and nondiagonal parton
distributions also hold after having evolved the different distributions.Comment: 17 pages, 6 figures, RevTex. Some figures have been corrected due to
a recently discovered small error in the evolution cod
Color coherent phenomena on nuclei and the QCD evolution equation
We review the phenomenon of color coherence in quantum chromodynamics (QCD),
its implications for hard and soft processes with nuclei, and its experimental
manifestations. The relation of factorization theorems in QCD with color
coherence phenomena in deep inelastic scattering (DIS) and color coherence
phenomena in hard exclusive processes is emphasized. Analyzing numerically the
QCD evolution equation for conventional and skewed parton densities in nuclei,
we study the onset of generalized color transparency and nuclear shadowing of
the sea quark and gluon distributions in nuclei as well as related phenomena.
Such novel results as the dependence of the effective coherence length on
and general trends of the QCD evolution are discussed. The limits of the
applicability of the QCD evolution equation at small Bjorken are estimated
by comparing the inelastic quark-antiquark- and two gluon-nucleon (nucleus)
cross sections, calculated within the DGLAP approximation, with the dynamical
boundaries, which follow from the unitarity of the matrix for purely QCD
interactions. We also demonstrate that principles of color coherence play an
important role in the processes of soft diffraction off nuclei.Comment: 58 pages, 19 figures, Revtex. Minor editor's changes, final version
published in J.Phys. G27 (2001) R23-6
Nuclear shadowing in deep inelastic scattering on nuclei: leading twist versus eikonal approaches
We use several diverse parameterizations of diffractive parton distributions,
extracted in leading twist QCD analyses of the HERA diffractive deep inelastic
scattering (DIS) data, to make predictions for leading twist nuclear shadowing
of nuclear quark and gluon distributions in DIS on nuclei. We find that the
HERA diffractive data are sufficiently precise to allow us to predict large
nuclear shadowing for gluons and quarks, unambiguously. We performed detailed
studies of nuclear shadowing for up and charm sea quarks and gluons within
several scenarios of shadowing and diffractive slopes, as well as at central
impact parameters. We compare these leading twist results with those obtained
from the eikonal approach to nuclear shadowing (which is based on a very
different space-time picture) and observe sharply contrasting predictions for
the size and Q^2-dependence of nuclear shadowing. The most striking differences
arise for the interaction of small dipoles with nuclei, in particular for the
longitudinal structure function F_{L}^{A}.Comment: 43 pages, 16 figures, requires JHEP style fil