Measurement of beam asymmetry for $\pi^-\Delta^{++}$ photoproduction on the proton at $E_\gamma$=8.5 GeV

TL;DR

This paper reports the first measurement of the beam asymmetry in $ o ext{pi}^- ext{Delta}^{++}$ photoproduction at 8.2-8.8 GeV, providing insights into meson exchange mechanisms and higher-order corrections at high energies.

Contribution

It presents the first experimental measurement of the beam asymmetry for this reaction at high photon energies, testing phenomenological models and exploring meson exchange processes.

Findings

Beam asymmetry $ o$ varies with momentum transfer $t$

Negative $ o$ at small $|t|$, positive $ o$ at large $|t|$

Reaction involves $t$-channel exchange with multiple intermediaries

Abstract

We report a measurement of the $\pi^-$ photoproduction beam asymmetry for the reaction $\vec{\gamma} p \rightarrow \pi^- \Delta^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $\Sigma$ is measured as a function of four-momentum transfer $t$ to the $\Delta^{++}$ and compared to phenomenological models. We find that $\Sigma$ varies as a function of $t$: negative at smaller values and positive at higher values of $|t|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy.