# Photoproduction of $\eta$ and $\eta'$ Mesons on Proton

## TL;DR

This paper presents new high-precision measurements of eta and eta prime meson photoproduction on protons, revealing a cusp at 1.9 GeV, and introduces an updated theoretical model incorporating 23 resonances and Regge phenomenology.

## Contribution

It provides the first high-precision data for eta and eta prime photoproduction and develops an improved etaMAID model with detailed resonance and background parametrization.

## Key findings

- Observation of a cusp at W~1.9 GeV in eta photoproduction.
- The cusp is explained as a threshold effect from the eta' p decay channel.
- The updated etaMAID model includes 23 resonances and Regge background.

## Abstract

New high-precision total and differential cross sections for $\eta$ and $\eta'$ photoproduction on the proton obtained by the A2 Collaboration at the Mainz Microtron are presented. The data for $\eta$ photoproduction demonstrate a cusp at the energy W$\sim$1.9~GeV. Furthermore, we present a new version of the $\eta$MAID model for $\eta$ and $\eta'$ photoproduction. The model includes 23 nucleon resonances parametrized with Breit-Wigner shapes. The background is described by vector and axial-vector meson exchanges in the $t$ channel using the Regge phenomenology. Parameters of the resonances were obtained from a fit to preliminary data of the A2 Collaboration at MAMI and available data from other collaborations. The cusp is explained as a threshold effect due to the opening $\eta' p$ decay channel of the $N(1895)1/2^-$ resonance.