Speaker
Description
In high energy heavy ion collisions, high $p_T$ direct photons emerge from initial hard scattering processes, unaffected by the color-charged medium, unlike jets and final state hadrons. These hadrons suffer energy losses, quantified through the nuclear modification factor, which compares $N_{coll}$(binary nucleon-nucleon collisions) scaled yields from $p+p$ collisions to those in heavy ion interactions, thereby revealing the influence of the medium on particle yields as a function of collision centrality. Despite longstanding contrary expectations, we observe an unexpected suppression of high-transverse-momentum neutral hadrons in high-activity events in smaller system collisions, and, conversely, an enhancement in more peripheral collisions—a phenomenon not typically seen in larger systems.
Our study, using data of $d$+Au collisions at $\sqrt{s_{NN}} = 200$ GeV from PHENIX, contrasts the production of direct photons and $\pi^0$ in $d$+Au collisions. This presentation will explore how a new method using direct direct photon production as a measure of $N_{coll}$ corrects this bias.
