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 < 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 12 C.
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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/c 2 ) in the 12 C(K − ,K + ) reaction at P K − = 1.66GeV/c using a scintillating fiber target. The differential cross section for the ΛΛ production averaged over 2.3° ≤ $$ K + ≤ 14.7° in the momentum region 0.95 ≤ p K + ≤ 1.3GeV/c was found to be 7.6 ± 1.3 μb/sr, and that for the enhancement approximately 3 μb/sr.
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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/ c 2 ) in the 12 C( 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≤ p K + ≤1.3 GeV/ c averaged over the range 2.3 o ≤ θ K + ≤14.7 o 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.
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Differential cross sections and photon beam asymmetries for the gamma p rightarrow K+ Lambda and gamma p rightarrow K+ Sigma0 reactions have been measured in the photon energy range from 1.5 GeV to 2.4 GeV and in the angular range from Theta_{cm} = 0 to 60 of the K+ scattering angle in the center of mass system at the SPring-8/LEPS facility. The photon beam asymmetries for both the reactions have been found to be positive and to increase with the photon energy. The measured differential cross sections agree with the data measured by the CLAS collaboration at cosTheta_{cm}<0.9 within the experimental uncertainties, but the discrepancy with the SAPHIR data for the K+Lambda reaction is large at cosTheta_{cm}>0.9. In the K+Lambda reaction, the resonance-like structure found in the CLAS and SAPHIR data at W=1.96 GeV is confirmed. The differential cross sections at forward angles suggest a strong K-exchange contribution in the t-channel for the K+Lambda reaction, but not for the K+Sigma0 reaction.
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.55 GeV (W=1.947 GeV).
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.65 GeV (W=1.994 GeV).
Photon beam asymmetries for the two reactions as a function of CM angle for photon beam energy 1.75 GeV (W=2.041 GeV).
Σ + p elastic scattering has been studied using a scintillating fiber block (SCIFI) which served as a target for the production of Σ + hyperons as well as for subsequent Σ + scattering on hydrogen. A new technique for the analysis of the hyperon-nucleon scattering in the SCIFI has been developed and established. In this paper, Σ + p elastic scattering events have been identified in the Σ + momentum range of 300–600 MeV/ c , and differential cross sections have been obtained at two angles. The results are compared with various theoretical baryon-baryon interaction models.
The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for $\gamma p \to \phi p$, $\gamma d \to \phi p n$ and $\gamma d \to \phi d$ at forward production angles. A linearly polarized photon beam at $E_{\gamma}$=1.6-2.4 GeV was used for the production of $\phi$ mesons. The natural-parity Pomeron exchange processes remains dominant nearthreshold. The unnatural-parity processes of pseudoscalar exchange is visible in the production from nucleons but is greatly reduced in the coherent production from deuterons. There is no strong $E_{\gamma}$-dependence, but some dependence on momentum-transfer. A small but finite value of the spin-density matrix elements reflecting helicity-nonconserving amplitudes in the $t$-channel is observed.
Measurements of the spin density matrix element RHO(JJ=0,MM=11) for the GAMMA P --> PHI P reaction in the Adair system as a function of T-Tmin for 3 incident photon energy regions.
Differential cross sections for $\gamma p \to K^+\Lambda(1405)$ and $\gamma p \to K^+\Sigma^0(1385)$ reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of $0.8<\cos(\Theta)<1.0$ for the $K^+$ scattering angle in the center-of-mass system. This data is the first measurement of the $\Lambda(1405)$ photoproduction cross section. The lineshapes of \LamS measured in $\Sigma^+\pi^-$ and $\Sigma^-\pi^+$ decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the $\Sigma\pi$ scattering amplitudes. The ratios of \LamS production to \SigS production were measured in two photon energy ranges: near the production threshold ($1.5<E_\gamma<2.0$ GeV) and far from it ($2.0 <E_\gamma<2.4$ GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.
Cross section for LAMBDA(1405) production.
Cross section for SIGMA(1385)0 production.
Photoproduction of $\Lambda$(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8/LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K$^{+/0}$ angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K$^+$ angles.
The measured differential cross sections from the liquid hydrogen target, protons, as a function the K+ polar angle.
The measured differential cross sections from the liquid hydrogen target, protons, as a function the photon energy at forward K+ polar angles of 19-43 degrees .
The measured of differential cross section at backward K+/K0 polar angles of 120-150 degrees as a function of photon energy from the liquid hydrogen target, protons, and liquid deuterium target, deuterons.
We report the measurement of the $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linearly polarized tagged-photon beams in the range of $E_{\gamma}=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $\gamma p \rightarrow K^{+}\Lambda$ and $\gamma p \rightarrow K^{+}\Sigma^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{\gamma}=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $\Lambda$ in the whole observed energy range. A lack of similar feature for $\Sigma^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.6 < cos(theta) < 0.7.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.7 < cos(theta) < 0.8.
Differential cross sections for the GAMMA P --> K+ LAMBDA reaction as a function of photon energy Egamma for the kaon c.m. production polar angle 0.8 < cos(theta) < 0.9.
A high statistics experiment was performed on Bhabha scattering at energies between 14 and 34 GeV. Good agreement with QED was observed. The combined data on Bhabha scattering and μ pair production were found to agree with the standard theory of electroweak interaction giving sin 2 θ = 0.27 −0.07 +0.06 . Assuming for the Z 0 mass a value of 90 GeV the leptonic weak coupling constants were determined to g V 2 = −0.04 ± 0.06 and g A 2 = 0.35 ± 0.09. A search for scalar leptons sets lower limits on the mass of scalar electrons of M s e > 16.6 GeV and of scalar muons of M s μ > 16.4 GeV.
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