Messung der Reaktionen γ p -> K⁺ Λ und γ p -> K⁺ Σ^o für Photonenergien bis 2.6 GeV mit dem SAPHIR-Detektor an ELSA

Abstract

The reactions γ p -> K⁺ Λ and γ p -> K⁺ Σ^o were measured in the energy range from threshold up to a photon energy of 2.6 GeV. The data were taken with the SAPHIR detector at the electron stretcher facility ELSA. Results on cross sections and on hyperon polarizations are presented as a function of kaon production angle and photon energy. <br /> The total cross section for Λ production rises steeply with energy close to threshold, whereas the Σ^o cross section rises slowly to a maximum at photon energies of about 1.45 GeV. <br /> Cross sections together with their angular decomposition into Legendre polynomials suggest contributions from resonance production for both reactions. The K⁺Λ differential cross section is enhanced for backward produced kaons at photon energies of about 1.45 GeV. This might be interpreted as contribution of a <i>missing resonance</i> D₁₃(1895), which has been proposed by model calculations.<br /> The polarization of Λ has in general positive values in kaon forward directions and negative values in backward directions. The magnitude varies with energy. The polarization of Σ^o follows a similar angular and energy dependence as that of Λ, but with opposite sign.