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 ° ~< 0 ~< 145 ° a parity violating asymmetry of Xcorr = ( 3.5 _+ 0.7 _+ 0.2) × 106 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 sin 2 0 w = 0.221 + 0.014 + 0.004.