Ξ− and Ξ+ production in central Pb+Pb collisions at 158 GeV/c per nucleon

Results of the production of Ξ− and Ξ+ hyperons are presented for the 10% most central Pb+Pb interactions at 158 GeV/c per nucleon where the average number of participants Npart is about 335. This analysis utilises a global reconstruction procedure, which allows a measurement of 4π integrated yields to be made for the first time. Inverse slope parameters, which are determined from an exponential fit to the transverse mass spectra, are found to be 267±9 MeV and 296±17 MeV for Ξ− and Ξ+ hyperons, respectively. Mid-rapidity densities (dN/dy) are found to be 1.49±0.08 and 0.33±0.04 particles per event per unit rapidity for Ξ− and Ξ+, respectively. The ratio R(Ξ+/Ξ−) at mid-rapidity, R(y=ycm), is found to be 0.22±0.03. Yields integrated to full phase space are found to be 4.12±0.20 and 0.77±0.04 particles per event for Ξ− and Ξ+ hyperons, respectively.