Probing the Partonic Degrees of Freedom in High-Multiplicity p-Pb collisions at sNN =5.02 TeV

Abstract

We investigate the role of partonic degrees of freedom in high-multiplicity p-Pb collisions at sNN=5.02 TeV carried out at the Large Hadron Collider (LHC) by studying the production and collective flow of identified hadrons at intermediate pT via the coalescence of soft partons from the viscous hydrodynamics (VISH2+1) and hard partons from the energy loss model, linear Boltzmann transport (LBT). We find that combining these intermediate pT hadrons with the low pT hadrons from the hydrodynamically expanding fluid and high pT hadrons from the fragmentation of quenched jets, the resulting hydro-dynamics-coalescence-fragmentation model provides a nice description of measured pT spectra and differential elliptic flow v2(pT) of pions, kaons, and protons over the pT range from 0 to 6 GeV. We further demonstrate the necessity of including the quark coalescence contribution to reproduce the experimentally observed approximate number of constituent quark scaling of hadron v2 at intermediate pT. Our results thus indicate the importance of partonic degrees of freedom and also hint at the possible formation of quark-gluon plasma in high-multiplicity p-Pb collisions at the LHC.