Near Threshold Hyperon-Production at COSY-11 in the Reactions pp->pK+Lambda and pp->pK+Sigma0


At the Cooler Synchrotron COSY in Jülich the production of strange particles has successfully been measured. At the internal COSY-11 experiment [1] a hydrogen cluster target is installed in front of a regular COSY-dipole. This magnet is used as a spectrometer for the reaction products. The detection system is based on drift chambers and scintillation-counters.
Near threshold data of the pp->pK+Lambda reaction have recently been published by the COSY-11 [2-4] and the COSY-TOF collaboration [5]. Since before these COSY-measurements no exclusive data in the threshold region were available, the present results have given input to theoretical models describing the strangeness production in baryon-baryon collisions. Investigations of the hyperon-production above the different Sigma-thresholds provides an understanding of the Sigma-production processes and of the possible Lambda-Sigma coupling (cusp-effect).
Therefore the COSY-11 collaboration has extended its program from the Lambda- to the Sigma0-production. After the presentation of the COSY-11 facility the results of the pp->pK+Sigma0 measurements [6] will be compared to the pp->pK+Lambda reaction. It was found, that the corresponding cross sections at equivalent excess energies near threshold are about a factor of 28 smaller for the Sigma0-production than for the Lambda-production.

S.Brauksiepe et al., Nucl. Instr. & Meth. A 376 (1996) 397
J.Balewski et al., Phys. Lett. B 388 (1996) 859
J.Balewski et al., Phys. Lett. B 420 (1998) 211
J.T.Balewski et al., Eur.Phys.J. A 2 (1998) 99
R.Bilger et al., Phys. Lett. B 420 (1998) 217
S.Sewerin et al., nucl-ex/981104

Abstract in PostScript format (89kB)
Complete document in PostScript format (354kB)
Publication: Nucl.Phys. A 663-664 (2000) 473-476