Abundance of Δ resonances in 58Ni + 58Ni collisions between 1 and 2 AGeV

Abstract

Charged pion spectra measured in 58 Ni 58 Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Δ resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Δ -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 Δ states at freeze-out for beam energies of 1 and 2 AGeV, respectively.