Beam-spin asymmetry $\boldsymbol{\Sigma}$ for $\Sigma^-$ hyperon photoproduction off the neutron

TL;DR

This paper presents new measurements of the beam-spin asymmetry in $oldsymbol{ ightarrow} K^+oldsymbol{ ightarrow} ightarrow ightarrow$ reactions off neutrons, providing crucial data to refine models of nucleon excited states and their couplings.

Contribution

It offers the first data at certain energies and angles, significantly constraining partial wave analyses and revealing the importance of previously unconsidered resonances.

Findings

Data show sensitivity to specific nucleon resonances.

Inclusion of data alters resonance coupling parameters.

New constraints improve understanding of nucleon excitation spectrum.

Abstract

We report a new measurement of the beam-spin asymmetry $\boldsymbol{\Sigma}$ for the $\vec{\gamma} n \rightarrow K^+\Sigma^-$ reaction using quasi-free neutrons in a liquid-deuterium target. The new dataset includes data at previously unmeasured photon energy and angular ranges, thereby providing new constraints on partial wave analyses used to extract properties of the excited nucleon states. The experimental data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS), housed in Hall B of the Thomas Jefferson National Accelerator Facility (JLab). The CLAS detector measured reaction products from a liquid-deuterium target produced by an energy-tagged, linearly polarised photon beam with energies in the range 1.1 to 2.3 GeV. Predictions from an isobar model indicate strong sensitivity to $N(1720)3/2^+$, $\Delta(1900)1/2^-$, and $N(1895)1/2^-$, with the latter being a state not considered in previous photoproduction analyses. When our data are incorporated in the fits of partial-wave analyses, one observes significant changes in $\gamma$-$n$ couplings of the resonances which have small branching ratios to the $\pi N$ channel.