Coulomb distortion of pi+/pi- as a tool to determine the fireball radius in central high energy heavy ion collisions

Abstract

We compute the Coulomb distortion produced by an expanding and highly charged fireball on the spectra of low transverse momenta and mid rapidity pions produced in central high energy heavy ion collisions. We compare to data on Au+Au at 11.6A GeV from E866 at the BNL AGS and of Pb+Pb at 158A GeV from NA44 at the CERN SPS. We match the fireball expanison velocity with the average transverse momentum of protons and find a best fit to the charged pion ratio when the fireball radius is about 10 fm at freeze-out. This value is common to both AGS and SPS data.

4 pages includes 2 figures, uses espcrc1 and epsfig. To appear in proceedings of QM99, Torino Italy, May 1999