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

The double strangeness exchange reaction (K-,K+) is investigated with respect to the subthreshold production of scalar and vector mesons (f0/a0/φ) decaying into K+K- and the two-step processes induced by intermediate mesons and Ξ- hyperons at pK-=1.66 GeV/c using a scintillating fiber active target. The differential cross section (left angle dσ/dΩL right angle) averaged over the angular interval (2.30 ≤ θK+L ≤ 14.70) for the sub-threshold f0/a0/φ meson production with the K+K- decay is 11±6 μb/sr at 0.6≤ pK+<0.95 GeV/c. The present result differs significantly from the theoretical calculation which predicts the contribution of the f0/a0/φ meson production to be predominant in the (K-,K+) reaction below pK+=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≤pK+<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 pK+ ≅1.1 GeV/c could be due to the Ξ-p→ΛΛ reaction in 12C. (orig.)