Photoproduction of $KΛ$ on the proton

Abstract

Kaon photoproduction on the proton is studied in the resonance region using an isobar model. The higher-spin nucleon (3/2 and 5/2) and hyperon (3/2) resonances were included in the model utilizing the consistent formalism by Pascalutsa and they were found to play an important role in data description. The spin-1/2 and spin-3/2 hyperon resonances in combination with the Born terms contribute significantly to the background part of the amplitude. Various forms of the hadron form factor were considered in the construction and the dipole and multidipole forms were selected as those most suitable for the data description. Model parameters were fitted to new experimental data from CLAS, LEPS, and GRAAL collaborations and two versions of the model, BS1 and BS2, were chosen. Both models provide a good overall description of the data for the c.m. energies from the threshold up to 2.4 GeV. Predicted cross sections of the models at very small kaon angles being consistent with results of the Saclay-Lyon model indicate that the models could be also successful in predicting the hypernucleus production cross sections. Although kaon photoproduction takes place in the third-resonance region with many resonant states, the total number of included resonances, 15 and 16, is quite moderate and it is comparable with numbers of resonances in other models. The set of chosen nucleon resonances overlaps well with the set of the most probable contributing states determined in the Bayesian analysis with the Regge-plus-resonance model. Particularly, we confirm that the missing resonances $P_{13}(1900)$ and $D_{13}(1875)$ do play important role in the description of data. However, the spin-1/2 state $P_{11}(1880)$ included in the Bayesian analysis was replaced in our analysis with the near-mass spin-5/2 state $N^*(1860)$, recently considered by the Particle Data Group.