Charged Pion Production In 2a To 8a Gev Central Au Plus Au Collisions

Momentum spectra of charged pions over nearly full rapidity coverage from target to beam rapidity have been extracted from 0-5% most central Au +Au collisions in the beam energy range from 2A to 8A GeV by the E895 experiment. Using a thermal parametrization to fit the transverse mass spectra, rapidity density distributions are extracted. The observed spectra are compared with predictions from the RQMD version 2.3 cascade model and also to a thermal model including longitudinal flow. The total 4pi yields of the charged pions are used to infer an initial-state entropy produced in the collisions.