Thermal photon radiation in high multiplicity p+Pb collisions at the Large Hadron Collider

Understand

The collective behaviour of hadronic particles has been observed in high multiplicity proton-lead collisions at the Large Hadron Collider (LHC), as well as in deuteron-gold collisions at the Relativistic Heavy-Ion Collider (RHIC).

• In this work we present the first calculation, in the hydrodynamic framework, of thermal photon radiation from such small collision systems.
• Owing to their compact size, these systems can reach temperatures comparable to those in central nucleus-nucleus collisions.
• The thermal photons can thus shine over the prompt background, and increase the low $p_T$ direct photon spectrum by a factor of 2-3 in 0-1% p+Pb collisions at 5.02 TeV.