Verlag des Forschungszentrums Jülich
JUEL-4184
Rozek, Tomasz
Threshold Hyperon Production in Proton-Proton Collisions at COSY-11
85 S., 2005
For the first time the pp → nK+Σ+ reaction has been measured in the threshold
region and the cross section was determined. The measurement was performed
at the COSY-11 detection system at two beam momenta Pbeam = 2.6 GeV/c and
2.74 GeV/c, corresponding to excess energies Q = 13 MeV and 60 MeV.
COSY-11 is an internal magnetic spectrometer experiment at the COoler SYnchrotron
and storage ring COSY in Jülich, Germany. It is equipped with scintillator
hodoscopes and drift chambers for charged particle detection and a scintillator/lead
sandwich detector for neutrons.
Experimentally, the Σ+ hyperon was identified via the missing mass technique,
by detecting the remaining reaction products - K+ meson and neutron. Extensive
background studies in the missing mass spectra have been performed and the possible
influence of the the higher partial waves on the detection efficiency discussed.
The investigation on the Σ+ production is a part of the Jong ongoing studies of
the hyperons production performed by the COSY-11 collaboration. In the previous
analysis of the Λ and Σ0 hyperon production in the pp → pK+Λ and pp → pK+Σ0
reactions, respectively, the unexpectedly high cross section ratio σ(Λ)/σ(Σ0) in the
dose to threshold region was observed. To explain this behavior, various theoretical
scenarios were proposed, but although they differ even in the dominant basic
reaction mechanism, all more or less reproduce the data. In order to get more Information
for disentangling the contributing reaction mechanisms, data from an other
isospin channel were taken, namely pp → nK+Σ+.
Within this thesis the method of the measurement and the data analysis is given.
The total cross section is presented and the results are discussed in view of available
theoretical models.
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