We investigate the measurement of Hanbury Brown–Twiss (HBT) photon correlations as an experimental tool to discriminate different sources of photon production. To showcase that HBT correlations can distinguish between such sources, we consider two different scenarios in which we enhance the yields from standard hydrodynamical simulations. In the first, additional photons are produced from the early preequilibrium stage computed from the “bottom-up” thermalization scenario. In the second, the thermal rates are enhanced close to the pseudocritical temperature $T_c\approx 155\text{MeV}$ using a phenomenological ansatz. We compute the correlators for relative momenta $q_{\mathrm{o}}$, $q_{\mathrm{s}}$, and $q_{\mathrm{l}}$ for different transverse pair momenta, $K_{\perp }$, and find that the longitudinal correlation is the most sensitive to different photon sources. Our results also demonstrate that including anisotropic preequilibrium rates enhances non-Gaussianities in the correlators, which can be quantified using the kurtosis of the correlators. Finally, we study the feasibility of measuring a direct photon HBT signal in the upcoming high-luminosity runs at the CERN Large Hadron Collider. Considering only statistical uncertainties, we find that with the projected $\approx {10}^{10}$ heavy-ion events a measurement of the HBT correlations for $K_{\perp }<1\text{GeV}$ is statistically significant.

• Received 5 November 2019
• Revised 4 March 2020
• Accepted 17 July 2020

DOI:https://doi.org/10.1103/PhysRevC.102.024915

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.

Published by the American Physical Society