Parity-Violating Asymmetry in the N-> ∆ Transition

The primary focus of the Q_weak experiment at Jefferson Lab is the recently published determination of the proton’s weak charge. To properly make corrections to the measured asymmetry, dedicated measurements were made of the parity-violating asymmetry at low Q² in inelastic e-p scattering at the N-> ∆ transition for two different beam energies. The asymmetries are used to extract an additional physics result, the low energy constant d_∆ , which is responsible for the Siegert term that causes the asymmetry to be non-zero even at the photon point (Q² =0). The d_∆ term is a measure of the hadronic parity violation in this transition. It has been shown [S.L. Zhu, et al. Phys. Rev. Lett. 87, 201802 (2001)] to be related to some puzzles in radiative hyperon decays. These theoretical analyses suggest potential values of d_∆ much larger than its natural scale. The measurements described here were done at beam energies of 877 MeV (Q² = 0.011 GeV² ) and 1165 MeV (Q² = 0.021 GeV² ) using the Q_weak apparatus. An overview of the motivations for the measurement, the experimental approach, and the status of the analysis will be presented.