Abstract
Nuclear collisions which produce a high pT prompt photon offer a useful way to study the dynamics of the hot, dense medium produced in these events. Being colorless, photons are not influenced by the hot, dense medium. Thus, the outgoing photon serves as a tag of the initial parton flavors, and measures the initial parton pT before it is quenched by passage through the medium. In 2015, ATLAS sampled 0.49 nb−1 and 26 pb−1 of Pb+Pb and pp data at 5.02 TeV, respectively, with a high-level photon trigger that selects pT>25 GeV photons with high efficiency. The larger prompt photon cross-section and integrated luminosity with respect to 2.76 TeV data allow for new differential studies of photon-jet correlations. In this talk, ATLAS results on photon-jet azimuthal and pT balance will be presented using photons with pT>60 GeV photons and R=0.4, pT>30 GeV jets. Double-differential distributions of the jet-to-photon pT ratio, xJγ, and of the azimuthal difference, Δϕ, is presented as a function of photon pT and event centrality.
Highlights
Jet production in nucleus–nucleus collisions with a high pT prompt photon offers an opportunity to study the energy loss of energetic partons traversing the hot, deconfined medium created in these events [1, 2, 3, 4].At leading order, the photon and the jet are produced back-to-back in the azimuthal plane, with equal transverse momenta
Heavy Ion Collider (RHIC) [5] and Pb+Pb collisions at the Large Hadron Collider (LHC) [6] have confirmed that, since photons are not strongly interacting, their production rates are not modified by the medium [7]
TQeCVDPbh+arPdb-sacnadtte√rinsg=ev5e.0n2tsT. eTVhipspwcoorlklisrieopnordtastaa samples recorded in 2015 with the ATLAS detector at the LHC, with integrated luminosities corresponding to 0.49 nb−1 and 26 pb−1, respectively
Summary
Jet production in nucleus–nucleus collisions with a high pT prompt photon offers an opportunity to study the energy loss of energetic partons traversing the hot, deconfined medium created in these events [1, 2, 3, 4].At leading order, the photon and the jet are produced back-to-back in the azimuthal plane, with equal transverse momenta. Jet production in nucleus–nucleus collisions with a high pT prompt photon offers an opportunity to study the energy loss of energetic partons traversing the hot, deconfined medium created in these events [1, 2, 3, 4]. The high-level trigger system was configured with an online photon pT threshold of 30 GeV and 20 GeV in the pp and Pb+Pb running, respectively, and required that the candidate passed a loose set of criteria on the electromagnetic shower shape [10].
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