YANO-KOONIN-PODGORETSKII PARAMETRIZATION OF THE HANBURY BROWN-TWISS CORRELATOR

The Yano-Koonin-Podgoretskii (YKP) parametrisation of Hanbury Brown-Tw iss (HBT) two-particle correlation functions opens new strategies for extracting the emission duration and testing the longitudinal expansio n in heavy-ion collisions. Based on the recently derived model-indepen dent expressions, we present a detailed parameter study of the EXP par ameters for a finite, hydrodynamically expanding source model of heavy -ion collisions. For the class of models studied here, we show that th e three YKP radius parameters have an interpretation as longitudinal e xtension, transverse extension and emission duration of the source in the YKP frame. This frame is specified by the fourth fit parameter, th e Yano-Koonin velocity which describes to a good approximation the vel ocity of the fluid element with highest emissivity and allows to test for the longitudinal expansion of the source. Deviations from this int erpretation of the YKP parameters are discussed quantitatively.