Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 24: Heavy Ion Reactions III, Ultrarelativistic Energies

HK 24.7: Talk

Tuesday, March 17, 1998, 16:00–16:15, P

Radial Collective Flow of Kaons in Heavy Ion Reactions — •Z.S. Wang and Amand Faessler — Institut f"ur Theoretische Physik, Universit"at T"ubingen, Auf der Morgenstelle 14, D-72076 T"ubingen

In heavy ion reactions, kaons are created from elementary hadron-hadron collisions which take place randomly in the reaction system. According to the spirit proposed by Fermi[1], multiple production of particles from energetic hadron-hadron collisions can be understood in a pure thermal picture. Therefore, collective motion of the kaons can be identified only by an observation of deviation from the thermal description. We have examined these aspects by looking to the transverse mass spectra of the kaons emitted at midrapidity in central heavy ion reactions at SIS energies (1-2 GeV/nucleon). If we assume that the kaons have no interaction with the nuclear environment after their production, the spectra do exhibit exactly a Boltzmann distribution. As soon as we introduce a repulsive mean field acting on the kaons, a shoulder-arm shape appears in the spectra deviating from the thermal Boltzmann distribution. The observed shape can be understood very well in terms of a common radial velocity of the kaons, indicating that the kaons have developed a collective motion as a consequence of their in-medium mean field.

[1] E. Fermi, Prog. Theor. Phys. 5, 570 (1950)