# Nucleon resonances in $\gamma p \to K^{*+} \Lambda$

## TL;DR

This study analyzes high-precision cross-section data for the reaction gamma p to K*+ Lambda using an effective Lagrangian approach, highlighting the importance of including nucleon resonances to accurately describe the data.

## Contribution

It introduces a comprehensive model including nucleon resonances and other exchanges to better understand the reaction mechanism and resonance contributions in gamma p to K*+ Lambda.

## Key findings

- Including at least two nucleon resonances improves data fit.
- The N(2060)5/2- resonance shapes the angular distribution near threshold.
- Predicted asymmetries differ from other models, emphasizing the need for spin observable data.

## Abstract

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.