Double differential production cross sections of pi(-) and pi(+) mesons and the number of participating protons have been measured in central Au + Au collisions at 1 A . GeV. At low pion energies the pi(-) yield is strongly enhanced over the pi(+) yield. The energy dependence of the pi(-)/pi(+) ratio is assigned to the Coulomb interaction of the charged pions with the protons in the reaction zone. The deduced Coulomb potential increases with increasing pion c.m. energy. This behavior indicates different freeze-out radii for different pion energies in the c.m. frame. (C) 1998 Elsevier Science B.V. References: 27
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