Subthreshold pion production with associated multiplicity selection in the reaction→π+X139

Abstract
We have measured the energy and angular dependence of charged-pion production, with associated multiplicity selection, in La + La collisions at 138, 183, and 246 MeV/nucleon. The pions are produced mainly in collisions with a large number of participants. The general behavior of the spectra is consistent with results at higher energies, but the yield of subthreshold pions depends much more strongly upon the target and projectile mass. The pion spectra at 246 MeV/nucleon exhibit a strong charge dependence.