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Bremsstrahlung photon contributions to parton energy loss at high virtuality Q2: A perturbative calculation at O(αsαem)

Amit Kumar* and Gojko Vujanovic†

  • *Contact author: amit.kumar@uregina.ca
  • †Contact author: gojko.vujanovic@uregina.ca
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Phys. Rev. C 112, 025204 – Published 29 August, 2025

DOI: https://doi.org/10.1103/bmmf-9zv5

Abstract

In this work, real photon production scattering kernels from jet-medium interactions in the QCD medium are perturbatively calculated using the higher-twist (HT) formalism. Focus is given towards real photon production from a highly virtual (and highly energetic) quark, taking into account heavy-quark mass scales [Phys. Rev. C 94, 054902 (2016)], fermion-boson conversion processes [Nucl. Phys. A 793, 128 (2007)], as well as coherence effects [Phys. Rev. C 105, 024908 (2022)]. A generalized factorization procedure, such as that used in e−A deep-inelastic scattering, is employed to derive an improved single-scattering medium-induced photon emission kernels that go beyond the traditional in-medium gluon exchange approximation. Diagrams with real-photon emission from the hard quark are classified based on the final-state particles, and include two types of scattering kernels at O(αemαs) giving the following final states: (i) real photon and real quark, (ii) real photon and real gluon. The collisional kernels, thus derived, include full phase factors from all nonvanishing diagrams and complete second-order derivative terms in the transverse momentum gradient expansion. Moreover, the calculation includes heavy-quark mass effects, thus exploring heavy-quark energy loss. The in-medium parton distribution functions and the related jet transport coefficients have a hard transverse momentum dependence (of the emitted gluon or photon) present within the phase factor. It is observed that the jet transport coefficients resemble the transverse-momentum-dependent parton distribution functions.

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Phys. Rev. C 112, 025204– Published 29 August, 2025
  • Received 20 February 2025
  • Revised 8 May 2025
  • Accepted 21 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

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