Improved limits on the weak, neutral, hadronic axial vector coupling constants from quasielastic scattering of polarized electrons.

In scattering polarized electrons (P1 = 44% by 9Be at an energy of 300 MeV at angles 115°⩽ϑ⩽145° a parity violating asymmetry of Acorr = (−3.5 ± 0.7 ± 0.2) × 10−6 was measured. After correction for finite electron polarization and background we deduce an experimental asymmetry of Acx = (−9.4 ± 1.8 ± 0.5) × 10−6. The quoted errors indicate the statistical and the systematic uncertainties, respectively. The asymmetry, which is dominated by the quasielastic cross section, is interpreted in terms of model-independent electron-nucleon coupling constants of the weak neutral current. The error limits in the sector of axial vector coupling constants have been improved by a factor of 3 over previous results. A model-dependent analysis for the Weinberg angle yields the result sin2θw = 0.221 ± 0.014 ± 0.004