Hyperon production at 200 and 900 GeV c.m. energy

The production of Λ's and Ξ−'s in proton-antiproton collisions at 200 and 900 GeV c.m. energy has been studied using decays observed in the UA5 streamer chambers. The results are compared to previously published 546 GeV data, to results from other experiments, and to four theoretical models. The Λ yield per inelastic event is estimated to be 0.42±0.11 at 200 GeV and 0.66±0.14 at 900 GeV. We find a mean number of Ξ−'s per inelastic collision of 0.03−0.02+0.04 at 200 GeV and 0.06−0.03+0.05 at 900 GeV. The average transverse momentum of Λ's in the rapidity region |y|⩽2 is found to be 0.80−0.14+0.20 GeV/c at 200 GeV and 0.74±0.09 GeV/c at 900 GeV. The average transverse momentum of Ξ−'s in the rapidity region |y|⩽3 is estimated to be 0.8−0.2+0.4 GeV/c at 200 GeV and 0.7−0.1+0.2 GeV/c at 900 GeV which is lower than the unexpectedly high value of 1.1±0.2 GeV/c measured at 546 GeV. The ratio of Ξ− production to Λ production in the region |y|⩽2, pt>1 GeV/c is 0.07−0.04+0.08 at 900 GeV. This value is consistent with the ratio found in e+e− collisions and lower energy pp collisions but lower than the value obtained at 546 GeV. The average particle composition of events at 200 and 900 GeV, estimated using UA5 data, is presented.