233 research outputs found
Constraints for nuclear gluon densities from DIS data
The dependence of the ratios of nuclear structure functions is
studied by performing QCD evolution of nuclear parton distribution functions.
The log slope of these ratios is very sensitive to the nuclear gluon
distribution function. Taking different parametrizations, we show that the NMC
data on the dependence of rule out the case
where nuclear shadowing (suppression) of gluons at is much larger
than the shadowing observed in the ratio . We also take into
account modifications to the DGLAP evolution by including gluon fusion terms
and see that the effect is small at present energies, and, in any case, a
strong gluon shadowing is not favored. The region studied () is
the most relevant for RHIC multiplicities.Comment: 4 pages, 3 postscript figures. Contributed to 37th Rencontres de
Moriond on QCD and Hadronic Interactions, Les Arcs, France, 16-23 Mar 200
The scale dependent nuclear effects in parton distributions for practical applications
The scale dependence of the ratios of parton distributions in a proton of a
nucleus and in the free proton, ,
is studied within the framework of the lowest order leading-twist DGLAP
evolution. By evolving the initial nuclear distributions obtained with the
GRV-LO and CTEQ4L sets at a scale , we show that the ratios
are only moderately sensitive to the choice of a specific modern
set of free parton distributions. We propose that to a good first
approximation, this parton distribution set-dependence of the nuclear ratios
can be neglected in practical applications. With this result, we
offer a numerical parametrization of for all parton flavours
in any , and at any and any GeV for
computing cross sections of hard processes in nuclear collisions.Comment: 14 pages, including 4 eps-figure
Effects of shadowing on Drell-Yan dilepton production in high energy nuclear collisions
We compute cross sections for the Drell-Yan process in nuclear collisions at
next-to-leading order (NLO) in \alpha_s. The effects of shadowing on the
normalization and on the mass and rapidity dependence of these cross sections
are presented. An estimate of higher order corrections is obtained from
next-to-next-to-leading order (NNLO) calculation of the rapidity-integrated
mass distribution. Variations in these predictions resulting from choices of
parton distribution sets are discussed. Numerical results for mass
distributions at NLO are presented for RHIC and LHC energies, using appropriate
rapidity intervals. The shadowing factors in the dilepton mass range 2 < M < 10
GeV are predicted to be substantial, typically 0.5 - 0.7 at LHC, 0.7 - 0.9 at
RHIC, and approximately independent of the choice of parton distribution sets
and the order of calculation.Comment: 13 pages, 9 eps figure
Global DGLAP fit analyses of the nPDF: EKS98 and HKM
The DGLAP analyses of the nuclear parton distribution functions (nPDF) based
on the global fits to the data are reviewed, and the results from EKS98 and HKM
are compared. The usefulness of measuring hard probes in collisions, at
the LHC in particular, is demonstrated.Comment: 10 pages, 3 figures. Contribution to CERN Yellow Report on Hard
Probes in Heavy Ion Collisions at the LH
Constraints for nuclear gluon shadowing from DIS data
The dependence of the ratios of the cross sections of deep inelastic
lepton--nucleus scattering is studied in the framework of leading twist, lowest
order perturbative QCD. The slope of the ratio is computed by using the DGLAP evolution equations, and shown
to be sensitive to the nuclear gluon distribution functions. Four different
parametrizations for the nuclear effects of parton distributions are studied.
We show that the NMC data on the dependence of
rule out the case where nuclear shadowing (suppression) of gluons at is much larger than the shadowing observed in the ratio . We also show that the possible nonlinear correction terms due to gluon
fusion in the evolution equations do not change this conclusion. Some
consequences for computation of RHIC multiplicities, which probe the region
x\gsim0.01, are also discussed.Comment: 11 pages, 3 eps figure
Nuclear parton distributions in the DGLAP approach
Determination of the nuclear parton distributions within the framework of
perturbative QCD, the DGLAP equations in particular, is discussed. Scale and
flavour dependent nuclear effects in the parton distributions are compared with
the scale and flavour independent parametrizations of HIJING and of the Hard
Probe Collaboration. A comparison with the data from deep inelastic
lepton-nucleus scattering and the Drell-Yan process in proton-nucleus
collisions is shown.Comment: 19 pages, 6 eps-figures, to appear in the Proceedings of the Hard
Probe Collaboratio
Enhanced charm hadroproduction due to nonlinear corrections to the DGLAP equations
We have studied the effects of nonlinear scale evolution of the parton
distribution functions to charm production in collisions at center-of-mass
energies of 5.5, 8.8 and 14 TeV. We find that the differential charm cross
section can be enhanced up to a factor of 4-5 at low . The enhancement is
quite sensitive to the charm quark mass and the renormalization/factorization
scales.Comment: 4 pages, 3 eps-figures. To appear in the proceedings of the
seventeenth international conference on Ultra-Relativistic Nucleus-Nucleus
Collisions (Quark Matter 2004
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