Importance of initial and final state effects for azimuthal correlations in p+Pb collisions

TL;DR

This study examines how initial and final state effects influence azimuthal correlations in p+Pb collisions, revealing that initial effects dominate in low multiplicity events at higher transverse momenta, while final effects are more significant in high multiplicity events.

Contribution

It couples Yang-Mills dynamics with a perturbative QCD cascade to disentangle initial and final state effects on azimuthal correlations in p+Pb collisions.

Findings

Initial state correlations dominate in low multiplicity events at pT>2 GeV.

Final state interactions are more influential in high multiplicity events.

Both initial and final effects impact azimuthal correlation observables depending on event multiplicity.

Abstract

We investigate the relative importance of initial and final state effects on azimuthal correlations of gluons in low and high multiplicity p+Pb collisions. To achieve this, we couple Yang-Mills dynamics of pre-equilibrium gluon fields (IP-GLASMA) to a perturbative QCD based parton cascade for the final state evolution (BAMPS) on an event-by-event basis. We find that signatures of both the initial state correlations and final state interactions are seen in azimuthal correlation observables, such as $v_2\left\lbrace2PC\right\rbrace(p_T)$, their strength depending on the event multiplicity and transverse momentum. Initial state correlations dominate $v_2\left\lbrace2PC\right\rbrace(p_T)$ in low multiplicity events for transverse momenta $p_T>2~{\rm GeV}$. While final state interactions are dominant in high multiplicity events, initial state correlations affect $v_2\left\lbrace2PC\right\rbrace(p_T)$ for $p_T>2~{\rm GeV}$ as well as the pT integrated $v_2\left\lbrace2PC\right\rbrace$.