Helicity Asymmetry in gamma p -> pi+ n with FROST

TL;DR

This paper reports on the measurement of the polarization observable E in the gamma p -> pi+ n reaction using the FROST experiment, providing new data to refine baryon resonance analyses.

Contribution

It presents the first polarization measurements of the reaction gamma p -> pi+ n with a polarized photon beam and polarized target at Jefferson Lab.

Findings

Preliminary data align with existing analyses at low energies.

Significant deviations observed at higher energies.

Results highlight the importance of polarization data for resonance studies.

Abstract

The main objective of the FROST experiment at Jefferson Lab is the study of baryon resonances. The polarization observable E for the reaction gamma p to pi+n has been measured as part of this program. A circularly polarized tagged photon beam with energies from 0.35 to 2.35 GeV was incident on a longitudinally polarized frozen-spin butanol target. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer. Preliminary polarization data agree fairly well with present SAID and MAID partial-wave analyses at low photon energies. In most of the covered energy range, however, significant deviations are observed. These discrepancies underline the crucial importance of polarization observables to further constrain these analyses.