Probing the Partonic Degrees of Freedom in High-Multiplicity $p\text{\ensuremath{-}}\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=5.02\text{ }\text{ }\mathrm{TeV}$

Probing the Partonic Degrees of Freedom in High-Multiplicity $p − Pb$ collisions at $\sqrt{s_{N N}} = 5.02 TeV$

Wenbin Zhao, Che Ming Ko, Yu-Xin Liu, Guang-You Qin, and Huichao Song

Phys. Rev. Lett. 125, 072301 – Published 12 August 2020

Abstract

We investigate the role of partonic degrees of freedom in high-multiplicity $p − Pb$ collisions at $\sqrt{s_{N N}} = 5.02 TeV$ 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 partons from the viscous hydrodynamics ( $VISH 2 + 1$ ) and hard partons from the energy loss model, linear Boltzmann transport (LBT). We find that combining these intermediate $p_{T}$ hadrons with the low $p_{T}$ hadrons from the hydrodynamically expanding fluid and high $p_{T}$ hadrons from the fragmentation of quenched jets, the resulting hydro-dynamics-coalescence-fragmentation model provides a nice description of measured $p_{T}$ spectra and 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.

Received 27 November 2019
Revised 30 May 2020
Accepted 13 July 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.072301

Physics Subject Headings (PhySH)

Collective flow QCD phase transitions Quark-gluon plasma Relativistic heavy-ion collisions

Nuclear Physics

Authors & Affiliations

Wenbin Zhao ^1,2, Che Ming Ko ³, Yu-Xin Liu^1,2,4, Guang-You Qin ^5,6, and Huichao Song ^1,2,4

¹Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China
²Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
³Cyclotron Institute and Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
⁴Center for High Energy Physics, Peking University, Beijing 100871, China
⁵Institute of Particle Physics and Key Laboratory of Quark and Lepton Physics (MOE), Central China Normal University, Wuhan, Hubei 430079, China
⁶Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94270, USA