Abstract
Abstract We present a phenomenological study of the associated production of a prompt photon and a heavy quark jet (charm or bottom) in Pb-Pb collisions at the LHC. This channel allows for estimating the amount of energy loss experienced by the charm and bottom quarks propagating in the dense QCD medium produced in those collisions. Calculations are carried out at next-to-leading order (NLO) accuracy using the BDMPS-Z heavy-quark quenching weights. The quenching of the single heavy-quark jet spectrum reflects fairly the hierarchy in the heavy quark energy loss assumed in the perturbative calculation. On the contrary, the single photon spectrum in heavy-ion collisions is only modified at low momenta, for which less heavy-quark jets pass the kinematic cuts. On top of single particle spectra, the two-particle final state provides a range of observables (photon-jet pair momentum, jet asymmetry, among others) which are studied in detail. The comparison of the photon-jet pair momentum, from p-p to Pb-Pb collisions, is sensitive to the amount of energy lost by the heavy-quarks and could therefore be used in order to better understand parton energy loss processes in the heavy quark sector.
Highlights
Quarks (CF = 4/3) and gluons (CA = 3) for D mesons and pions, respectively
We present a phenomenological study of the associated production of a prompt photon and a heavy quark jet in Pb-Pb collisions at the LHC
We argue that measuring prompt photon production in association with a heavy quark tagged jet in heavy-ion collisions might shed light on the mass dependence of the radiative parton energy loss mechanism
Summary
Heavy quark mass terms m2Q/μ2 have been neglected in the perturbative calculation of the partonic cross sections where the factorization/renormalization scale μ is identified with a typical hard scale of the process, that is the transverse momentum of the photon or the jet.. We discuss the calculation of γ + Q production in heavy-ion collisions, in which the final-state partons propagating through the dense QCD medium are expected to lose energy through medium-induced gluon radiation, or radiative energy loss processes.. Beyond the leading order a second parton (labeled “2”) is produced in real 2 → 3 subprocesses (see table 1) The emission of this extra parton occurs within the short-distance time scale O Q−1 1 fm (where Q ΛQCD is the scale of the hard process), well before the medium is produced. Using the modified four-vectors we evaluate observables (pT Q, pT γ), as well as the correlation variables discussed in section 2.4 in which we bin the events, providing the differential cross section for these observables
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