Speaker
Description
Strong highly boosted electromagnetic fields are equivalent to a flux of quasi-real photons, such as the fields created in ultrarelativistic heavy ion colliders like the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). The copious flux of photons allows, for the first time, detailed studies of high-energy photon-nucleus collisions which at the LHC can reach center of mass energies of 1 TeV. One interesting question is whether photonuclear collisions are characterized by a momentary hot deconfined QCD-mediated state of matter, which is the dominant paradigm of nucleus-nucleus collisions at similar energies. This talk details the first dedicated collection and analysis of high-multiplicity photon-Pb collisions at the LHC. Results are presented for a search for signatures of an evolving QCD medium (commonly modeled with relativistic hydrodynamics) and other basic properties of photon-Pb collisions. Significant hydrodynamic-like behavior is observed and theorized to arise from the photon fluctuations into a di-quark hadronic states which are resolved by the Pb target, resembling proton-nucleus collisions where similar signatures have also been detected. The measurements of photonuclear collisions are compared to proton-Pb collisions as well as theoretical models based on hydrodynamics and alternatively initial-state momentum anisotropy. This work demonstrates the accessibility and utility of photonuclear collisions for a broad range of research in hadron physics as well as foreshadows and compliments research at future electron-ion colliders.
