Unresolved issues in nuclear photon flux calculations for high-energy photons produced inside the nucleus

Determine a theoretically robust and experimentally validated treatment of the coherent nuclear photon flux in ultra-peripheral heavy-ion collisions, with particular emphasis on accurately modeling higher-energy photons produced inside the nucleus, so that predictions of photonuclear jet production cross-sections are reliable across the relevant kinematic range.

Background

Accurate predictions of photonuclear jet production in ultra-peripheral Pb+Pb collisions depend critically on the modeling of the coherent nuclear photon flux. The paper employs an Equivalent Photon Approximation with impact-parameter constraints and further corrections from the Starlight generator, and discusses how these choices affect comparisons with data.

Despite recent progress and validation using processes such as ultra-peripheral dilepton production, the authors point out that aspects of the photon flux remain unsettled, especially the treatment of higher-energy photons produced inside the nucleus. This uncertainty is directly relevant for interpreting measured photonuclear jet cross-sections and for constraining nuclear parton distribution functions.