Measurement of the reactions pp → ∑+∑+ and pp → ∑−∑− close to threshold

The reactions pp → ∑+∑+ and pp → ∑−∑− have been investigated at GeV/c beam momentum by the PS185 Collaboration at LEAR, CERN. Of both reaction types together 170 events could be identified. The cross section of the reaction pp → ∑+∑+ was determined to be σtot = 3.68 ± 0.43 μb at an excess energy of 23 MeV. Its angular distribution exhibits a pronounced forward peaking. The ratio of the cross sections σ(pp → ∑+∑+)σ(pp → ∑−∑−) = 2.4−1.3+3.0 was extracted with a confidence limit of 90%. It is the first time that experimental data of these reaction channels are available close to the threshold. We compare our results with those of earlier experiments and with theoretical predictions.