Probing collectivity in ultra-relativistic heavy ion collision by leptons and photons

TL;DR

This paper investigates the signatures of collectivity in ultra-relativistic heavy ion collisions through leptons and photons, analyzing flow indicators and correlations to understand phase transitions and matter properties.

Contribution

It introduces a novel approach to probe collectivity using lepton and photon correlations, and provides predictions for LHC energies based on RHIC data.

Findings

Variation of HBT radii with invariant mass indicates collectivity.

Radial velocity ratios from photon and lepton spectra serve as phase transition indicators.

Simultaneous reproduction of $v_2^{HF}$ and $R_{AA}$ at RHIC energies.

Abstract

It has been shown that the evolution of collectivity in ultra-relativistic heavy ion collision is manifested in the variation of various HBT radii with invariant mass ($M$) extracted from the correlation functions of two lepton pairs. The value of the radial velocity ($v_r$) can be estimated from the ratio of the $p_T$ distributions of single photons to lepton pairs for various $M$ windows. It has been argued that the variation of radial flow with appropriate kinematic variables can be used as an indicator of a phase transition from initially produced partons to hadrons. We also consider the elliptic flow ($v_2^{HF}$) of the matter as probed by the single electron spectra originating from the semileptonic decays of heavy mesons. The measured values of $v_2^{HF}$ and the nuclear suppression factor ($R_{\mathrm AA}$) at RHIC energy have been reproduced simultaneously by including both the collisional and radiative processes within the scope of perturbative quantum chromodynamics. The $R_{\mathrm AA}$ and $v_2^{HF}$ have been predicted for LHC energy.