# Study of $\eta$ and $\eta'$ photoproduction at MAMI

## TL;DR

This study measures $ o$ and $ o'$ photoproduction reactions at MAMI with high precision, revealing a cusp near the $ o'$ threshold and providing insights into the $N(1895)1/2^-$ resonance.

## Contribution

It offers the first high-accuracy differential cross sections for these reactions and constrains the properties of the $N(1895)1/2^-$ resonance through a revised isobar model.

## Key findings

- Observation of a cusp at the $ o'$ threshold
- Confirmation of the $N(1895)1/2^-$ resonance's decay channels
- Enhanced understanding of $ o$ and $ o'$ production mechanisms

## Abstract

The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $\eta$ photoproduction at the energies in vicinity of the $\eta'$ threshold, $W=1896$MeV ($E_\gamma=1447$MeV). This behavior is explained in a revised $\eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $\eta p$ and $\eta' p$, confirming the existence and constraining the properties of this poorly known state.