sPHENIX measurements of isolated photon production in p+p collisions

The sPHENIX experiment at RHIC is a next-generation collider detector optimized for rare probes of the Quark-Gluon Plasma (QGP), including jets, photons, and heavy-flavor particles. The detector features large-acceptance, electromagnetic (EMCal) and hadronic (HCal) calorimeter systems, each covering over 2 units in pseudorapidity and full azimuthal angle, integrated with a high-rate trigger and data acquisition system.

During RHIC Run-24, sPHENIX recorded 107 pb^-1 of p+p collisions at 200 GeV, employing an efficient high-p_T photon trigger. This dataset represents nearly an order-of-magnitude increase in luminosity × acceptance compared to previous EMCal-based measurements at this energy, and marks the first use of a mid-rapidity HCal at RHIC.

This talk presents a measurement of the isolated photon production cross section in p+p collisions, utilizing—for the first time at RHIC—an isolation criterion based on the full EMCal+HCal calorimeter system. This measurement serves as a critical standard candle for the sPHENIX calorimeter performance and provides an essential perturbative QCD (pQCD) baseline for future studies of isolated photons and photon+jet correlations in sPHENIX Au+Au data. The measured cross section is found to be in good agreement with next-to-leading order (NLO) pQCD predictions, validating the performance of the calorimeter system and the photon isolation methodology.