The Emission Pattern of High-Energy Pions: A New Probe for the Early Phase of Heavy Ion Collisions

Abstract

The emission pattern of charged pions has been measured in Au+Au collisions at 1 GeV/nucleon incident energy. In peripheral collisions and at target rapidities, high-energy pions are emitted preferentially towards the target spectator matter. In contrast, low-energy pions are emitted predominantly in the opposite direction. The corresponding azimuthal anisotropy is explained by the interaction of pions with projectile and target spectator matter. This interaction with the spectator matter causes an effective shadowing which varies with time during the reaction. Our observations show that high-energy pions stem from the early stage of the collision whereas low-energy pions freeze out later.

accepted for publication in Phys. Rev. Lett

References in corpus (2)

• Transverse momentum analysis of collective motion in relativistic nuclear collisions
• Evidence for Different Freeze-Out Radii of High- and Low-Energy Pions Emitted in Au+Au Collisions at 1 GeV/nucleon

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