PHOTON SPIN AND THE SHAPE OF THE 2-PHOTON CORRELATION-FUNCTION

We use the covariant current formalism to derive the general form of t he 2-photon correlation function for fully chaotic sources. Motivated by the recent discussion in the literature we concentrate on the effec ts from the photon spin on the correlator. We show that for locally th ermalized expanding sources, like those expected to be created in rela tivistic heavy ion collisions, the only change relative to 2-pion inte rferometry is a statistical factor 1/2 for the overall strength of the correlation which results from the experimental averaging over the ph oton spin.