Abundance of Delta Resonances in 58Ni+58Ni Collisions between 1 and 2 AGeV

Charged pion spectra measured in 58Ni-58Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Delta resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Delta-resonance decay to the component of thermal pions, deduced from the high transverse momentum part of the pion spectra. About 10 and 18% of the nucleons are excited to Delta states at freeze-out for beam energies of 1 and 2 AGeV, respectively.Comment: 14 pages, LaTeX with 3 included figures; submitted to Physics Letters

Entropy production in the Au + Au reaction between 150 and 800 A MeV

The entropy per nucleon (S/A) has been extracted for the Au [(150—800)A MeV] + Au reaction by using the phase I setup of the 4 pi facility at GSI, Darmstadt. The entropy has been obtained from the comparison of various observables characterizing the dM/dZ fragment multiplicity distributions, extending up to Z~15, with those calculated with the quantum statistical model. It is the first time that S/A values are determined by considering the full ensemble of charged products detected in the reaction. Consistent values of S/A are found from different methods. These entropy values are shown to be fairly independent of the volume of the ``participant'' region considered. They are somewhat lower than those extracted in earlier works but are in good agreement with hydrodynamic calculations and suggest a low viscosity for the hot and dense nuclear matter

Proton-proton correlations in central collisions of Ni-Ni at 1.93 A.GeV and the space-time extent of the emission source

Small-angle correlations of proton pairs produced in central Ni+Ni collisions at a beam energy of 1.93 A.GeV are investigated with the FOPI detector system at GSI Darmstadt. A well-defined emission source is selected by triggering on central events which comprise about 8% of the total cross section. Simultaneous comparison of longitudinal and transverse correlation functions with the predictions of the Koonin model allows to unravel the space-time ambiguity of the emission process. Taking into account the strong collective expansion of the participant zone, which introduces a reduction of the extracted source radius of more than 30%, r.m.s. radius and emission time parameters of R_r_m_s = (4.2#+-#1.2) fm and t_r_m_s = (11"+"7_-_5) fm/c are extracted, respectively. In contrast, the analysis of the angle-integrated correlation function gives an upper limit R_r_m_s = (7.0 #+-# 1.4) fm of the source radius. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman