Determination of nuclear parton distributions

Abstract

Parametrization of nuclear parton distributions is investigated in the leading order of alpha_s. The parton distributions are provided at Q^2=1 GeV^2 with a number of parameters, which are determined by a chi^2 analysis of the data on nuclear structure functions. Quadratic or cubic functional form is assumed for the initial distributions. Although valence quark distributions in the medium x region are relatively well determined, the small x distributions depend slightly on the assumed functional form. It is difficult to determine the antiquark distributions at medium x and gluon distributions. From the analysis, we propose parton distributions at Q^2=1 GeV^2 for nuclei from deuteron to heavy ones with the mass number A~208. They are provided either analytical expressions or computer subroutines for practical usage. Our studies should be important for understanding the physics mechanism of the nuclear modification and also for applications to heavy-ion reactions. This kind of nuclear parametrization should also affect existing parametrization studies in the nucleon because "nuclear" data are partially used for obtaining the optimum distributions in the "nucleon".Comment: 16 pages, REVTeX4b5, revtex4.cls, url.sty, natbib.sty, 10pt.rtx, aps.rtx, revsymb.sty, 21 eps figures. Submitted for publication. Computer codes for the nuclear parton distributions could be obtained from http://www-hs.phys.saga-u.ac.jp Email: kumanos@cc.saga-u.ac.j

Electromagnetic signatures of the color glass condensate: dileptons

“…We also show the nuclear modification factor for the proton-gold collisions for sake of comparison. It should be noted that nuclear shadowing of the incoming deuteron wave function is taken into account in the HKM parameterization [16]. As is clear from the figure, there is a large difference between dilepton production in proton-gold and deuteron-gold collisions as there must be since the flavor and as a result, electric charge, decomposition of proton and deuteron are different.…”

“…We note that, in this kinematic region, the incoming quark or anti-quark distributions in a proton are well known and there is very little difference between different parameterizations. For a deuteron projectile, we use the HKM parameterization [16] of the F d 2 structure function which includes shadowing. Again, since the projectile quarks and anti-quarks are in the large x bj region, the nuclear effects in the projectile deuteron are not large except at very large x bj ∼ 0.7 − 0.9 where shadowing can be a 20% − 30% effect.…”

Modified Paschos-Wolfenstein relation and extraction of the weak mixing anglesin2θW

“…The weight functions are defined at fixed Q 2 (=1 GeV 2 ) in Ref. [12]; however, they are used at any Q 2 throughout this paper. The explicit Q 2 dependence is abbreviated as for the PDFs.…”

Z0 production as a test of nuclear effects at the LHC

“…For example, the HIJING parameterization includes impact parameter dependence, but does not deal with the scale dependence [16,17]. On the other hand, the EKS98 [18] and HKM [19] parameterizations have a scale dependence, but do not consider impact parameter dependence. (The latter parameterizations have been compared recently [20].)…”