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

An investigation of high-transverse-momentum (high-𝑝𝑇) photon-triggered jets in proton-proton (𝑝−𝑝) and ion-ion (𝐴−𝐴) collisions at √𝑠𝑁⁢𝑁=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 (𝑅𝐴⁢𝐴) for inclusive jets and high-𝑝𝑇hadrons. We obtain a good reproduction of the experimental data for photon-triggered jet 𝑅𝐴⁢𝐴, as measured by the ATLAS detector, the distribution of the ratio of jet to photon 𝑝𝑇 (𝑋𝐽⁢𝛾), 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 𝐼𝐴⁢𝐴, 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 𝑋𝐽⁢𝛾>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.