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Register a new userMeasurement of $K^- p$ radiative capture to $gamma Lambda$ and $gamma Sigma^0$ for $p_{K^-}$ between 514 and 750 MeV/$c$
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Differential cross sections for $K^-$ radiative capture in flight on the proton, leading to the $gammaLambda$ and $gammaSigma^0$ final states, have been measured at eight $K^-$ momenta between 514 and 750 MeV/$c$. The data were obtained with the Crystal Ball multiphoton spectrometer installed at the separated $K/pi$ beam line C6 of the BNL Alternating Gradient Synchrotron. The results substantially improve the existing experimental data available for studying radiative decays of excited hyperon states. An exploratory theoretical analysis is performed within the Regge-plus-resonance approach. According to this analysis, the $gammaSigma^0$ final state is dominated by hyperonresonance exchange and hints at an important role for a resonance in the mass region of 1700 MeV. In the $gammaLambda$ final state, on the other hand, the resonant contributions account for only half the strength, and the data suggest the importance of a resonance in the mass region of 1550 MeV.
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Differential cross sections and hyperon polarizations have been measured for $bar{K}^0 n$, $pi^0 Lambda$, and $pi^0 Sigma^0$ production in $K^- p$ interactions at eight $K^-$ momenta between 514 and 750 MeV/$c$. The experiment detected the multiphoton final states with the Crystal Ball spectrometer using a $K^-$ beam from the Alternating Gradient Synchrotron of BNL. The results provide significantly greater precision than the existing data, allowing a detailed reexamination of the excited hyperon states in our energy range.
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.
This work measured $dsigma/dOmega$ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $gamma prightarrow K^0Sigma^+$, $gamma nrightarrow K^0Lambda$, and $gamma nrightarrow K^0 Sigma^0$ reactions. Our results for $gamma nrightarrow K^0 Sigma^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $pi N$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.
The high-precision cross-section data for the reaction $gamma p to K^{*+}Lambda$ reported by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility have been analyzed based on an effective Lagrangian approach in the tree-level approximation. Apart from the $t$-channel $K$, $kappa$, $K^*$ exchanges, the $s$-channel nucleon ($N$) exchange, the $u$-channel $Lambda$, $Sigma$, $Sigma^*(1385)$ exchanges, and the generalized contact term, the contributions from the near-threshold nucleon resonances in the $s$-channel are also taken into account in constructing the reaction amplitude. It is found that, to achieve a satisfactory description of the differential cross section data, at least two nucleon resonances should be included. By including the $N(2060){5/2}^-$ resonance, which is responsible for the shape of the angular distribution near the $K^*Lambda$ threshold, and one of the $N(2000){5/2}^+$, $N(2040){3/2}^+$, $N(2100){1/2}^+$, $N(2120){3/2}^-$ and $N(2190){7/2}^-$ resonances, one can describe the cross-section data quite well, with the fitted resonance masses and widths compatible with those advocated by the Particle Data Group. The resulted predictions of the beam, target, and recoil asymmetries are found to be quite different from various fits, indicating the necessity of the spin observable data for $gamma p to K^{*+}Lambda$ to further pin down the resonance contents and associated parameters in this reaction.
The process $gamma gamma to p bar{p} K^+ K^-$ and its intermediate processes are measured for the first time using a 980~fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The production of $p bar{p} K^+ K^-$ and a $Lambda(1520)^0~(bar{Lambda}(1520)^0)$ signal in the $pK^-$~($bar{p} K^+$) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/$c^2$, denoted as $Theta(1540)^0$~($bar{Theta}~(1540)^0$) or $Theta(1540)^{++}$~($Theta(1540)^{--}$), is seen in the $p K^-$~($bar{p}K^+$) or $pK^+$~($bar{p} K^-$) invariant mass spectra. Cross sections for $gamma gamma to p bar{p} K^+ K^-$, $Lambda(1520)^0 bar{p} K^+ +c.c.$ and the products $sigma(gamma gamma to Theta(1540)^0 bar{p} K^+ +c.c.)BR(Theta(1540)^0 to p K^{-})$ and $sigma(gamma gamma to Theta(1540)^{++} bar{p} K^- +c.c.)BR(Theta(1540)^{++}to p K^{+})$ are measured. We also determine upper limits on the products of the $chi_{c0}$ and $chi_{c2}$ two-photon decay widths and their branching fractions to $p bar{p} K^+ K^-$ at the 90% credibility level.
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