Gluon shadowing and hadron production in heavy-ion collisions at LHC

TL;DR

This paper analyzes gluon shadowing effects in heavy-ion collisions at LHC, using recent charged hadron multiplicity data to refine models and predict centrality dependence at different energies.

Contribution

It provides a combined fit of LHC and RHIC data to constrain gluon shadowing parameters and offers predictions for hadron multiplicity at various energies and centralities.

Findings

Good agreement between data and HIJING2.0 predictions.

Reduced uncertainty in gluon shadowing parameter $s_g$.

Centrality dependence is largely energy-independent for most centralities.

Abstract

The recently published first measurement of charged hadron multiplicity density at mid-rapidity $dN_{ch}/d\eta=1584 \pm 4 ({\rm stat.}) \pm 76 ({\rm sys.})$ in central $Pb+Pb$ collisions at $\sqrt{s} = 2.76$ TeV by the ALICE Experiment at LHC is in good agreement with the HIJING2.0 prediction within the experimental errors and theoretical uncertainties. The new data point is used to carry out a combined fit together with the RHIC data to reduce the uncertainty in the gluon shadowing parameter $s_{g}$ which controls the overall magnitude of gluon shadowing at small fractional momentum $x$ in HIJING2.0 model. Predictions on the centrality dependence of charged hadron multiplicity density at mid-rapidity with reduced uncertainty are given for $Pb+Pb$ collisions at $\sqrt{s}=2.76$ and 5.5 TeV. The centrality dependence is surprisingly independent of the colliding energy as compared to RHIC energy for most of centralities starting at $N_{\rm part}=50$ (100) at $\sqrt{s}=2.76$ (7) TeV. However, it becomes stronger in peripheral collisions at higher colliding energies.