Central Pb+Pb collisions at 158 A GeV/c studied by interferometry

Two-particle correlations have been measured for identified pi(-) from central 158 A GeV Pb+Pb collisions and fitted radii of about 7 fm in all dimensions have been obtained. A multi-dimensional study of the radii as a function of k(gamma) is presented, including a full correction for the resolution effects of the apparatus. The cross term R-out-long(2) of the standard fit in the Longitudinally CoMoving System (LCMS) and the upsilon(L) parameter of the generalised Yano-Koonin fit are compatible with 0, suggesting that the source undergoes a boost invariant expansion. The shapes of the correlation functions in Q(inv) and Q(space) = root<(Q(x)(2) + Q(y)(2) + Q(z)(2))over bar> have been analyzed in detail. They are not Gaussian but better represented by exponentials. As a consequence, fitting Gaussians to these correlation functions may produce different radii depending on the acceptance of the experimental setup used for the measurement.