Measurement of the Parity-Violating Asymmetry in the N to $\hat{I}”$ Transition at Low $Q^2$

Abstract

We report the measurement of the parity-violating asymmetry in the N to $\hat{I}”$ transition via the $e^{-}+p\to e^{-}+\hat{I}{”}^{+}$ 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, $d_{\hat{I}}”$, 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 $\hat{I}{\pounds }^{+}\to p{\hat{I}}^3$. The measurements reported here constrain $d_{\hat{I}}”$ 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 $d_{\hat{I}}”$, consistent with zero, in the strangeness-conserving channel, in contrast to the large value for $d_{\hat{I}}”$ previously reported in the strangeness-changing channel.

6 pages, 1 figure