Measurement of the Parity-Violating Asymmetry in the N to $Δ$ Transition at Low $Q^2$
nucl-ex
/ Authors
D. Adhikari, T. Alshayeb, D. Androic, D. S. Armstrong, A. Asaturyan, K. Bartlett, R. S. Beminiwattha, J. Benesch, F. Benmokhtar, R. D. Carlini
and 63 more authors
J. C. Cornejo, S. Covrig Dusa, M. M. Dalton, C. A. Davis, W. Deconinck, J. A. Dunne, D. Dutta, W. S. Duvall, M. Elaasar, W. R. Falk, J. M. Finn, C. Gal, D. Gaskell, M. T. W. Gericke, J. R. Hoskins, D. C. Jones, P. M. King, E. Korkmaz, S. Kowalski, J. Leacock, J. P. Leckey, A. R. Lee, J. H. Lee, L. Lee
/ Abstract
We report the measurement of the parity-violating asymmetry in the N to $Δ$ transition via the $e^- + p \rightarrow e^- + Δ^+$ reaction at two different kinematic points with low four-momentum transfer Q$^2$. Measurements were made with incident electron beam energies of 0.877 and 1.16 GeV, corresponding to $Q^2$ values of 0.0111 and 0.0208 (GeV/c)$^2$, respectively. These measurements put constraints on a low-energy constant in the weak Lagrangian, $d_Δ$, corresponding to a parity-violating electric-dipole transition matrix element. This matrix element has been shown to be large in the strangeness-changing channel, via weak hyperon decays such as $Σ^+ \rightarrow pγ$. The measurements reported here constrain $d_Δ$ in the strangeness-conserving channel. The final asymmetries were -0.65 +- 1.00 (stat.) +- 1.02 (syst) ppm (parts per million) for 0.877 GeV and -3.59 +- 0.82 (stat.) +- 1.33 (syst.} ppm for 1.16 GeV. With these results we deduce a small value for $d_Δ$, consistent with zero, in the strangeness-conserving channel, in contrast to the large value for $d_Δ$ previously reported in the strangeness-changing channel.