Updated version.

Abstract:

Decrease of HBT radii with m_t has an established interpretation as a signal of transverse expansion believed to be a collective property of heavy ion collisions. Paradoxically such a decrease has also been seen in e+e- collisions[1]. Correlations of non-identical mesons, being sensitive to a difference in space-time emission patterns of light and heavier particles, and thus to transverse expansion, cross-check the interpretations. STAR presents correlations of identical charged ππ and Kπ in light systems (pp, dAu). We use spherical harmonics to capture the features of the two-particle correlation in the space of momentum differences. We use own and established models (such as HIJING) to associate longer range features with effects of energy-momentum conservation on the global and binary-collision scale. At lower momentum difference, ππ and Kπ correlations due to HBT and/or Coulomb effects paint a qualitatively consistent if unexpected picture of transverse collectivity.
[1] OPAL, CERN-PH-EP/2007-025