Tilted Pion Sources from Azimuthally Sensitive HBT Interferometry

by Urs Wiedemann (CERN-TH)

Tuesday 4 Apr 2000, 14:00 → 14:15 Europe/Zurich

CERN

Intensity interferometry in noncentral heavy ion collisions provides access to novel and unexplored information on the geometry of the effective pion-emitting source. My discussion focuses mainly on the new discovery that even for vanishing pair momentum, the cross terms RRSUB>ol² and R_sl² of the HBT correlation function in general show a strong first harmonic in their azimuthal dependence. The strength of this oscillation characterises the tilt of the major axis of the emission ellipsoid within the reaction plane away from the direction of the beam. Event generator studies indicate that this tilt can be large (>20 degrees) at AGS energies which makes it by far the most significant azimuthally sensitive HBT signal at these energies. Moreover, transport models suggest that for pions this spatial tilt is directed opposite to the tilt of the directed flow ellipsoid in momentum space. A measurement of the azimuthal dependence of the HBT cross terms R_ol² and R_sl² thus probes directly the physical origin of pion directed flow.

Organiser(s): Yiota Foka and Ulrich Heinz

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