In heavy ion collisions resonances can create strong non-Gaussian eects in the 2-pion correlation data. Hence, the commonly used Gaussian t parameters do not fully characterize these correlators. We suggest a dierent set of HBT parameters which does not presuppose a particular shape of the correlator and allows to extract additional (non-Gaussian) information. Within a simple model for an expanding source including resonance decays it is shown that this additional information provides a clean

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... stinction between scenarios with and without transverse ow. PACS numbers: 25.75.+r, 07.60.ly, 52.60.+h The aim of Hanbury-Brown/Twiss (HBT) interferometric analyses of heavy ion collisions is to extract from the measured 2-particle correlators C(q; K) of identical particles as much information as possible about the spatio-temporal distribution S(x; K) of the particle emitting sources in the collision region. It is based on the relation [1, 2]