Near-threshold Lambda(1520) production by the gamma p -> K+Lambda(1520) reaction at forward K+ angles

Differential cross sections and photon-beam asymmetries for the gamma p -> K+ Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump structure was found at W=2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with J<=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with J>=5/2 or by a new reaction process, for example an interference effect with the phi photoproduction having a similar bump structure in the cross sections.Comment: 5 pages, 4 figures, published in Phys. Rev. Let

Measurement of the γ⃗p→K+Λ\vec{\gamma} p \to K^+ \Lambda Reaction at Backward Angles

Cross sections for the $\gamma p \to K^+ \Lambda$ have been measured at backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV. In addition, the beam asymmetry for this reaction has been measured for the first time at backward angles. The $\Lambda$ was detected at forward angles in the LEPS spectrometer via its decay to $p\pi^-$ and the K^+ was inferred using the technique of missing mass. These measurements, corresponding to kaons at far backward angles in the center-of-mass frame, complement similar CLAS data at other angles. Comparison with theoretical models shows that the reactions in these kinematics provide further opportunities to investigate the reaction mechanisms of hadron dynamics.Comment: 6 figures, submitted to PRC rapid communication

Possibility of determinig the parity of the pentaquark Θ+\Theta^+ from photoproduction near threshold

We discuss the possibility of determining the parity of the $\Theta^+$ baryon from photoproduction $\gamma N\to K\Theta^+$ process near threshold. We utilize the conservation laws of parity and angular momentum for the analysis of angular distributions and spin observables near threshold. Since the discussion is in essence a partial wave analysis of the production mechanism the result should be less dependent on the model parameters. Our analysis shows that the angular distribution and photon polarization asymmetry for the process of neutron target are sensitive to the parity of the $\Theta^+$, but not for the case of proton target. In the case of proton target, the polarization asymmetries of target and recoiled $\Theta^+$ are preferred for parity determination.Comment: 23 pages, 13 figures, extended versio

Differential cross section and photon-beam asymmetry for the γ - p→π+n reaction at forward π+ angles at Eγ=1.5 -2.95 GeV

© 2018 American Physical Society. Differential cross sections and photon-beam asymmetries for the γ - p→π+n reaction have been measured for 0.

Differential Cross Section and Photon-Beam Asymmetry for the γ → p → π- Δ++ (1232) Reaction at Forward π- Angles for Eγ=1.5-2.95 GeV

Differential cross sections and photon-beam asymmetries for the →γp→π−Δ++(1232) reaction have been measured for 0.7 \u3c cosθc.m.π \u3c 1 and Eγ=1.5–2.95  GeV at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for 1.5 \u3c Eγ(GeV) \u3c 2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure u¯u quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Eγ=1.5–1.8  GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of π exchange in the t channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a d¯d or an s¯s quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data