Threshold Production of Sigma⁺ at COSY-11

T.Rozek for the COSY-11-Collaboration
Institute of Physics, Silesian University, Katowice, Poland,
IKP, Forschungszentrum Jülich

At the cooler synchrotron COSY the threshold production of hyperons has been studied via the pp->pK⁺Lambda(Sigma⁰) reaction [1] resulting in a cross section ratio R = sigma(Lambda) / sigma(Sigma⁰) of about 28 which exceeds the ratio at high energies by an order of magnitude. Possible explanations within different models are proposed [2] but a definite conclusion is up to now not possible. Further studies in other isospin channels like the Sigma⁺ production will help in the clarification of the relevant dominant reaction mechanisms.

The Sigma⁺ production was measured at the COSY-11 installation via the pp->nK⁺Sigma⁺ reaction at Q = 13 MeV and Q = 60 MeV. COSY-11 is an internal magnetic spectrometer experiment at the COoler SYnchroton and storage ring COSY in Jülich. It is equipped with scintillator hodoscopes and drift chambers for charged particle detection and a scintillator/lead sandwich detector for neutrons.

The status of the current analysis will be presented and discussed.

[1]

J.T.Balewski et al., PLB 420 (1998) 211,
S. Sewerin et al.,PRL 83 (1999) 682.,
P. Kowina, PhD thesis 2002.

[2]

A. Gasparian et al., PLB 480 (2000) 273, NPA 684:397, 2001,
R. Shyam et al., PRC63 (2001) 022202,
A. Sibirtsev et al., NPA646 (1999) 427, nucl-th/0004022 v2 (2000).