Hanbury-Brown-Twiss correlation of bremsstrahlung photons in nuclear collisions

The dimension of the region emitting particles in nuclear collisions can be determined by Hanbury-Brown and Twiss (HBT) correlations of identical particles. In thiss note we demonstrate that this dimension as determined by the HBT correlation of bremsstrahlung photons is larger than the actual one due to the photon formation length. Qualitatively r2 → r2 + a/ω2 where the last term is due to the formation length being proportional to 1/ω, where ω is the energy of the photon. This phenomenon permits to “see” experimentally the photon formation length.