Direct photons at low transverse momentum -- a QGP signal in pp collisions at LHC

TL;DR

This paper explores how thermal photon production in proton-proton collisions at 7 TeV can signal quark-gluon plasma formation, with yields increasing quadratically with multiplicity, especially in high-multiplicity events.

Contribution

It demonstrates that thermal photons can dominate over prompt photons at low transverse momentum in pp collisions, indicating potential QGP signals in small systems.

Findings

Thermal photon yields increase quadratically with charged particle multiplicity.

Thermal photons dominate prompt photons at pT < 10 GeV/c in high-multiplicity events.

Significant thermal photon production occurs even in minimum bias pp collisions.

Abstract

We investigate photon production in a scenario of quark-gluon plasma formation in proton-proton scattering at 7 TeV. It is shown that thermal photon yields increase quadratically with the charged particle multiplicity. This gives an enhanced weight to high multiplicity events, and leads to an important photon production even in minimum bias events, where the thermal photons largely dominate over the prompt ones at transverse momentum values smaller than 10 GeV/c.