Lawrence Berkeley National Laboratory

Abstract. 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 $$k_T$$ is presented, including a full correction for the resolution effects of the apparatus. The cross term $$R^2_{out-long}$$ of the standard fit in the Longitudinally CoMoving System (LCMS) and the $$v_L$$ 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 $$Q_{space}=\sqrt{Q^2_x+Q^2_y+Q^2_z}$$ 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.