T. Iijima

Measurement of the Ξ−p scattering cross sections at low energy

Abstract In this Letter we report on the cross-section measurements for Ξ − p elastic and inelastic scatterings at low energy using an active scintillating fiber target. Upper limit for the total cross section of the elastic scattering was found to be 24 mb at 90% confidence level, and the total cross section for the Ξ − p → Λ Λ reaction was found to be 4.3 −2.7 +6.3 xa0mb . We compare these results with currently competing theoretical estimates.

Enhanced ΛΛ production near threshold in the 12C(K−,K+) reaction

Abstract Enhanced production of ΛΛ pairs, above levels predicted by a two-step process model, has been observed near threshold (in the mass range 2.23-2.26 GeV/c2) in the 12C(K−,K+) reaction at 1.66 GeV/c using a scintillating fiber target. The differential cross section for ΛΛ production in the momentum region 0.95≤pK+≤1.3 GeV/c averaged over the range 2.3o≤θK+≤14.7o was found to be 7.6±1.3 ±0.9 μ b/sr, and that for the enhancement was found to be approximately 3 μ b/sr.

Search for double-Λ hypernuclei and the H-dibaryon in the (K−,K+) reaction on 12C

Abstract A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .

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 μ b/sr at 0.6 ⩽ p K 1 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 + 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 12 C.

H-dibaryon search via the (K-,K+) reaction using a diamond target (BNL-E885)

Abstract An experiment to study double-strangeness systems was performed at the BNL-AGS via the (K − ,K + ) reaction using a diamond target and scintillating fiber (SCIFI) blocks (E885). A search for the H dibaryon through the stopped Ξ − process is one of the objectives. The number of stopped Ξ − s is about 9,000, and the expected sensitivity of the H dibaryon search is more than one order of magnitude higher than that of the previous experiment at KEK-PS (E224).

Enhanced production of ΛΛ pairs near threshold in the (K-,K+) reaction on 12C

Abstract Enhanced production of ΛΛ pairs, above the prediction of a two-step process model, is observed near threshold (around the masses of 2.23 – 2.26 GeV/c2) in the12C(K−,K+) reaction at PK− = 1.66GeV/c using a scintillating fiber target. The differential cross section for the ΛΛ production averaged over 2.3° ≤

Xi-P Scattering and STOPPED-Xi-12C Reaction

K + ≤ 14.7° in the momentum region 0.95 ≤ pK + ≤ 1.3GeV/c was found to be 7.6 ± 1.3 μb/sr, and that for the enhancement approximately 3 μb/sr.