Photon production from Pb+Pb collisions at {$\sqrt{s_{\rm {NN}}}$} = 5.02 TeV at LHC and at {$\sqrt{s_{\rm {NN}}}$} = 39 TeV at FCC

TL;DR

This study compares photon production and flow in Pb+Pb collisions at LHC and FCC energies, revealing significant increases in photon yields but minimal changes in elliptic flow, using hydrodynamical models and photon rates.

Contribution

It provides the first detailed comparison of prompt and thermal photon production at LHC and FCC energies, highlighting energy-dependent enhancements and flow characteristics.

Findings

Prompt photon yield increases by a factor of 1.5 to 2 at LHC energy and 5 to 15 at FCC.

Thermal photon production shows greater relative enhancement at FCC compared to LHC.

Photon elliptic flow remains relatively unchanged across different collision energies.

Abstract

We calculate the production of prompt and thermal photons from Pb+Pb collisions at 5.02A TeV at the Large Hadron Collider (LHC) and at 39A TeV at the proposed Future Circular Collider (FCC) facility. The photon spectra and anisotropic flow at these energies are compared with the results obtained from 2.76A TeV Pb+Pb collisions at the LHC for three different centrality bins. The prompt photons originating from initial hard scatterings are found to increase by a factor of 1.5 to 2 at 5.02A TeV in the $p_T$ region 2 to 15 GeV and the enhancement is found to be about 5 to 15 times at FCC energy compared to 2.76A TeV in the same $p_T$ region. The evolution of the Quark-Gluon Plasma (QGP) formed in Pb+Pb collisions at LHC and FCC energies are studied using a hydrodynamical model and the $p_T$ spectra and elliptic flow of thermal photons are calculated using state-of-the-art photon rates. The relative enhancement in the production of thermal photons is found to be more compared to prompt photons at FCC than at the LHC energies. Although the production of direct (prompt+thermal) photons is found to enhance significantly with increase in beam energy, the photon elliptic flow increases only marginally and does not show strong sensitivity to the collision energy.