Measurement of spin-density matrix elements in $\ensuremath{\rho}(770)$ production with a linearly polarized photon beam at ${E}_{\ensuremath{\gamma}}=8.2--8.8 \mathrm{GeV}$

Measurement of spin-density matrix elements in $ρ (770)$ production with a linearly polarized photon beam at $E_{γ} = 8.2 - 8.8 GeV$

S. Adhikari et al. (GlueX Collaboration)

Phys. Rev. C 108, 055204 – Published 15 November 2023

Abstract

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5 GeV$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$ (770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$ -channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$ dependence of natural- and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ (770)$ differ by two units are negligible for $- t < 0.5 {GeV}^{2} / c^{2}$ .