# Differential Cross Section Measurements for $\gamma n\to\pi^-p$ Above the First Nucleon Resonance Region

## TL;DR

This paper reports extensive measurements of the differential cross sections for gamma-neutron to pion-proton reactions above the first nucleon resonance, providing new data that refine resonance analysis and determine photon decay amplitudes for the first time.

## Contribution

It presents a large set of new differential cross section data for gamma-neutron to pion-proton reactions, significantly increasing the available statistics and enabling improved resonance analysis and extraction of decay amplitudes.

## Key findings

- 8428 new data points for cross sections
- First determination of photon decay amplitudes at resonance poles
- Enhanced constraints on N* resonance spectrum

## Abstract

The quasi-free $\gamma d\to\pi^{-}p(p)$ differential cross section has been measured with CLAS at photon beam energies $E_\gamma$ from 0.445 GeV to 2.510 GeV (corresponding to $W$ from 1.311 GeV to 2.366 GeV) for pion center-of-mass angles $\cos\theta_\pi^{c.m.}$ from -0.72 to 0.92. A correction for final state interactions has been applied to this data to extract the $\gamma n\to\pi^-p$ differential cross sections. These cross sections are quoted in 8428 $(E_\gamma,\cos\theta_\pi^{c.m.})$ bins, a factor of nearly three increase in the world statistics for this channel in this kinematic range. These new data help to constrain coupled-channel analysis fits used to disentangle the spectrum of $N^*$ resonances and extract their properties. Selected photon decay amplitudes $N^* \to \gamma n$ at the resonance poles are determined for the first time and are reported here.