The linear correlation coefficient vs. the cross term in Bose-Einstein correlations

We investigate the nature of the new cross term for Gaussian parameterizations of Bose-Einstein correlations of identical particles emitted from purely chaotic hadron sources formed by relativistic heavy ion collisions. We find that this additional parameter in the so-called Bertsch-Pratt parameterization can be expressed in terms of a linear “out-longitudinal” correlation coefficient for emission of bosons and two already known “radius” parameters, Rl and Ro. The linear correlation coefficient is of kinematical origin and can be used to determine the widths of longitudinal momentum distributions.