Probing the partonic degrees of freedom in high multiplicity p-Pb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV

TL;DR

This study uses a combined hydrodynamics and coalescence model to analyze high multiplicity p-Pb collisions at 5.02 TeV, revealing evidence for partonic degrees of freedom and possible quark-gluon plasma formation.

Contribution

It introduces a Hydro-Coal-Frag model that successfully describes hadron spectra and flow, emphasizing the role of partonic interactions in small collision systems.

Findings

Model reproduces $p_T$ spectra and $v_2$ for identified hadrons.

Quark coalescence is essential for quark number scaling of $v_2$.

Results suggest partonic degrees of freedom and QGP formation in p-Pb collisions.

Abstract

We investigate the role of partonic degrees of freedom in high multiplicity p-Pb collisions at $\sqrt{s_{NN}}=$ 5.02 TeV carried out at the Large Hadron Collider (LHC) by studying the production and collective flow of identified hadrons at intermediate $p_T$ via the coalescence of soft and hard partons generated from viscous hydrodynamics (VISH2+1) and the energy loss model (LBT), respectively. We find that combining the intermediate $p_T$ hadrons from the coalescence with the low $p_T$ hadrons from hydrodynamics and high $p_T$ hadrons from the jet fragmentation, our Hydro-Coal-Frag model provides a nice description of the measured $p_T$-spectra and the differential elliptic flow $v_2(p_T)$ of pions, kaons and protons over the $p_T$ 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 $v_2$ at intermediate $p_T$. 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.