Analysis of hard two-photon correlations measured in heavy-ion reactions at intermediate energies

Recently reported measurements of hard photon correlations in the reactions Ar-36 on Al-27 at 95A MeV, Kr-86 on Ni-nat at 60A MeV, and Ta-181 on Au-197 at 39.5A MeV are analyzed. A Boltzmann-Uhling-Uhlenbeck transport model is used to describe the photon production by individual nucleon-nucleon collisions. In the lighter systems we find the best agreement with data when taking into account only photons from first-chance collisions of nucleons or photons produced during the passage of the nuclei, while the model predicts also a considerable late-time emission of photons, which leads to a depletion of the calculated correlation function. The accuracy of the present data does not allow firm conclusions on the reliability of this late-time evolution. Our investigations do not support a recently reported interference pattern in the heavy Ta + Au system.