Effects of shadowing in Pb + Pb collisions at energies available at the CERN Large Hadron Collider within the HIJING code

Abstract

The charged particle central rapidity density per participant nucleon pair ( $(\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ ) as a function of the average number of participants ( $ N_{part}$ ) for $ \mathrm{Au}+\mathrm{Au}$ ( $ \mathrm{Cu}+\mathrm{Cu}$ ) collisions at $ \sqrt{s_{\mathrm{NN}}}=62.4$ and 200 GeV, and $ \mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and 5.02 TeV is investigated within an improved HIJING (ImHIJING/Cas) model. Compared to the standard HIJING version, it incorporates: i) more consistent parton densities, ii) a QCD running coupling, defined by the exact solution of the renormalization group equation, and iii) a spatial dependent nucleon shadowing, triggered by collective nucleon interactions with an incoming nucleon, and simulated by the collective cascade recipe. Predictions are compared using four different settings of nuclear shadowing of partons, based on the standard HIJING1.0(2.0) parameterizations. It is shown that ImHIJING/Cas/Set2 (that with both quark and soft gluon shadowing of strength $ s_{q(g)}$ can nicely reproduce the measured centrality dependence of $ (\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ at RHIC energy. As for LHC, a reduction of $ s_{g}$ by $ \sim 40$ % at very peripheral (90-100%) $ \mathrm{Pb}+\mathrm{Pb}$ collisions, as compared to free nucleon-nucleon collisions, is found to reproduce the measured data. The values of $s_{q(g)}$ used in ImHIJING/Cas/Set2 calculations for most central 0-3(5)% $ \mathrm{Au}+\mathrm{Au} (\mathrm{Pb}+\mathrm{Pb})$ collisions at RHIC(LHC) energy, are found to be consistent with those employed in Set2 that reproduce the measured structure function ratios ( $ 12F^{Pb}_{2}/207F^{C}_{2}$ ) as a function of x.