7,012 research outputs found
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
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
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
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
Nuclear size and rapidity dependence of the saturation scale from QCD evolution and experimental data
The solutions of the Balitsky-Kovchegov evolution equations are studied
numerically and compared with known analytical estimations. The rapidity and
nuclear size dependences of the saturation scale are obtained for the cases of
fixed and running coupling constant. These same dependences are studied in
experimental data, on lepton-nucleus, deuteron-nucleus and nucleus-nucleus
collisions, through geometric scaling and compared with the theoretical
calculations.Comment: 8 pages, 8 figures. Contribution based on talks given by J. G.
Milhano and C. A. Salgado to the proceedings of ``Hard Probes 2004'',
Ericeira (Portugal), November 4-10, 200
- …