Pion freeze-out time in Pb+Pb collisions at 158?AGeV/c studied via π-/π+ and K-/K+ ratios

摘要

The effect of the final state Coulomb interaction on particles produced in Pb+Pb collisions at 158?AGeV/c has been investigated in the WA98 experiment through the study of the π-/π+ and K-/K+ ratios measured as a function of mT-m0. While the ratio for kaons shows no significant mT dependence, the π-/π+ ratio is enhanced at small mT-m0 values with an enhancement that increases with centrality. A silicon pad detector located near the target is used to estimate the contribution of hyperon decays to the π-/π+ ratio. The comparison of results with predictions of the RQMD model in which the Coulomb interaction has been incorporated allows to place constraints on the time of the pion freeze-out.