Nucleon resonances in γ p → K*+Λ

摘要

The high-precision cross section data for the reaction γp → K~(*+)Λ 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, κ,K~* exchanges, the s-channel nucleon (N) exchange, the u-channel Λ,∑,∑~*(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~*Λ 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 γp → K~(*+)Λ to further pin down the resonance contents and associated parameters in this reaction.