title: 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.
authors.affiliation: Technische Universitat Darmstadt, D-64289 Darmstadt, Germany.
authors.initials: A
authors.lastname: Wagner
authors.initials: C
authors.lastname: Muntz
authors.initials: H
authors.lastname: Oeschler
authors.initials: C
authors.lastname: Sturm
authors.initials: R
authors.lastname: Barth
authors.initials: M
authors.lastname: Cieslak
authors.initials: M
authors.lastname: D&ecedil;bowski
authors.initials: E
authors.lastname: Grosse
authors.initials: P
authors.lastname: Koczon
authors.initials: F
authors.lastname: Laue
authors.initials: M
authors.lastname: Mang
authors.initials: D
authors.lastname: Miskowiec
authors.initials: E
authors.lastname: Schwab
authors.initials: P
authors.lastname: Senger
authors.initials: P
authors.lastname: Beckerle
authors.initials: D
authors.lastname: Brill
authors.initials: Y
authors.lastname: Shin
authors.initials: H
authors.lastname: Strobele
authors.initials: W
authors.lastname: Walus
authors.initials: B
authors.lastname: Kohlmeyer
authors.initials: F
authors.lastname: Puhlhofer
authors.initials: J
authors.lastname: Speer
authors.initials: IK
authors.lastname: Yoo