Hard-photon-triggered jets in p−p and A−A collisions

Abstract

An investigation of high-transverse-momentum (high-pT) photon-triggered jets in proton-proton (p−p) and ion-ion (A−A) collisions at sNN=0.2 and 5.02TeV is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous study of the nuclear modification factor (RAA) for inclusive jets and high-pT hadrons. We obtain a good reproduction of the experimental data for photon-triggered jet RAA, as measured by the ATLAS detector, the distribution of the ratio of jet to photon pT (XJγ), measured by both CMS and ATLAS, and the photon-jet azimuthal correlation as measured by CMS. We obtain a moderate description of the photon-triggered jet IAA, as measured by STAR. A noticeable improvement in the comparison is observed when one goes beyond prompt photons and includes bremsstrahlung and decay photons, revealing their significance in certain kinematic regions, particularly at XJγ>1. Moreover, azimuthal angle correlations demonstrate a notable impact of bremsstrahlung photons on the distribution, emphasizing their role in accurately describing experimental results. This work highlights the success of the multistage model of jet modification to straightforwardly predict (this set of) photon-triggered jet observables. This comparison, along with the role played by bremsstrahlung photons, has important consequences on the inclusion of such observables in a future Bayesian analysis. Published by the American Physical Society 2025