Measurement of double polarisation asymmetries in $\omega$-photoproduction

TL;DR

This paper reports the first measurements of polarization asymmetries in omega-meson photoproduction off protons, revealing significant resonance contributions and providing new insights into baryon resonance dynamics.

Contribution

It presents the first experimental measurements of the beam-target-helicity asymmetries $E$ and $G$ in omega-photoproduction, covering a wide energy range and full solid angle, with implications for baryon resonance studies.

Findings

Significant contributions from $J^P=3/2^+, 5/2^+, 3/2^-$ partial waves.

Evidence of both $s$-channel resonance and $t$-channel exchange processes.

High sensitivity of $E$ and $G$ to baryon resonance contributions.

Abstract

The first measurements of the beam-target-helicity-asymmetries $E$ and $G$ in the photoproduction of $\omega$-mesons off protons at the CBELSA/TAPS experiment are reported. $E$ ($G$) was measured using circularly (linearly) polarised photons and a longitudinally polarised target. $E$ was measured over the photon energy range from close to threshold ($E_\gamma = 1108$~MeV) to $E_\gamma = 2300$~MeV and $G$ at a single energy interval of $1108 < E_\gamma <1300$~MeV. Both measurements cover the full solid angle. The observables $E$ and $G$ are highly sensitive to the contribution of baryon resonances, with $E$ acting as a helicity filter in the $s$-channel. The new results indicate significant $s$-channel resonance contributions together with contributions from $t$-channel exchange processes. A partial wave analysis reveals strong contributions from the partial waves with spin-parity $J^P=3/2^+, 5/2^+$, and $3/2^-$.