Scalar and vector meson production and two-step processes in the ( K−, K+) reaction on 12C

Abstract

The double strangeness exchange reaction ( K −, K +) is investigated with respect to the sub-threshold production of scalar and vector mesons ( f 0/ a 0/ φ) decaying into K + K − and the two-step processes induced by intermediate mesons and Ξ − hyperons at p k − = 1.66 GeV/ c using a scintillating fiber active target. The differential cross section ( 〈 dσ dΩ L 〉) averaged over the angular interval (2.3° ⩽ θ K + L ⩽ 14.7°) for the sub-threshold f 0/ a 0/ φ meson production with the K + K − decay is 11 ± 6 μb/sr at 0.6 ⩽ p K 1 < 0.95 GeV/ c. The present result differs significantly from the theoretical calculation which predicts the contribution of the f 0/ a 0/ φ meson production to be predominant in the ( K −, K +) reaction below p K + = 0.95 GeV/ c. We found a sizable contribution from two-step ( K −, K + processes, characterized by production of two S = −1 hyperons, consistent with the result of the intra-nuclear cascade (INC) model calculation with respect to the meson-induced hyperon (or hyperon resonance) pair production in the momentum region 0.6 ⩽ p K + < 0.95 GeV/ c. The observed enhancement of the cross section for the two-step ΛΛ production beyond the prediction of the INC model at p K + ⋍ 1.1 GeV/c could be due to the Ξ − p → ΛΛ reaction in 12C.