Exploring QGP-like phenomena with Charmonia in $p+p$ collisions at $\sqrt{s} = 13$ TeV

TL;DR

This study investigates whether small proton-proton collisions at 13 TeV can produce a thermalized QCD medium by examining charmonium production and suppression mechanisms, suggesting potential QGP-like phenomena.

Contribution

It models the evolution of charmonium states in small collision systems considering pre-equilibrium and thermalized stages, incorporating various suppression and regeneration mechanisms.

Findings

Charmonium yield is affected by gluonic dissociation and collisional damping.

Regeneration mechanisms can enhance charmonium production.

Combined effects of mechanisms serve as probes for thermalized QCD matter in small systems.

Abstract

In ultrarelativistic collisions of nuclei at the Large Hadron Collider, the created QCD environment rapidly changes, leading to a non-adiabatic evolution of the quantum states involved. Considering this, we first examine the pre-equilibrium state of QCD matter and its effect on the initially produced charmonium using a temperature-independent Hamiltonian. As the QCD matter reaches local thermal equilibrium, this Hamiltonian transforms to its finite temperature counterpart. To model the pre-equilibrium stage, we use the bottom-up thermalization approach to determine the effective temperature of the QCD matter, followed by a Gubser-type expansion for the thermalized medium. Additionally, we consider collisional damping, gluonic dissociation, and regeneration mechanisms, which specifically modify the charmonium yield in the thermalized medium. Mainly, the gluonic dissociation and collisional damping cause a reduction in the yield conversely, regeneration through gluonic deexcitation enhances the yield of charmonium. Further, we explore the combined effects of these mechanisms on the collective yield of charmonium states with transverse momentum ($p_{\rm T}$) and event multiplicity in the proton-proton collisions at $\sqrt{s} = 13$ TeV. Based on our findings, we contend that the combined effects of these mechanisms can serve as a robust probe for determining the possible existence of a thermalized QCD medium in such a small collision system.