title: Thermal Photon Radiation in High Multiplicity p+Pb Collisions at the Large Hadron Collider.
abstract: The collective behavior of hadronic particles has been observed in high multiplicity proton-lead collisions at the Large Hadron Collider, as well as in deuteron-gold collisions at the Relativistic Heavy-Ion Collider. 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. This thermal photon enhancement can therefore serve as a signature of the existence of a hot quark-gluon plasma during the evolution of these small collision systems, as well as validate hydrodynamic behavior in small systems.
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: Chun
authors.initials: C
authors.lastname: Shen
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Paquet
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.|Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Gabriel S
authors.initials: GS
authors.lastname: Denicol
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: Sangyong
authors.initials: S
authors.lastname: Jeon
authors.affiliation: Department of Physics, McGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada.
authors.forename: Charles
authors.initials: C
authors.lastname: Gale