Detection of the weak neutral current using fission anti ν/sub e/ on deuterons with concurrent measurement of the charged current branch

The target consists of 268 kg of extremely pure (99.85%) heavy water (D2O), contained in a cylindrical stainless steel tank 122 cm in height and 54 cm in diameter. This target is surrounded by a lead and cadmium shield and immersed in a 2200 liter liquid scintillator anticoincidence detector. This system is a well-shielded environment. The center of the detector is located 11 meters from the center of the reactor core in an electron antineutrino flux of 2.5 x 1013 anti ν/sub e//cm2-s. Immersed in the target are ten 5.08-cm-diameter 3He-filled gas proportional counters, which detect the neutron via the reaction 3He + n → p + 3H + 773 keV. The system has been determined to have an overall neutron detection efficiency of 0.32 +- 0.02. The data are taken with a combination of scalers, a pulse height analyzer, and oscilloscope traces. Single, double, and triple neutron capture events are recorded with the reactor on and off. Data have been accumulated for 104 live days reactor on, and 72 live days reactor off for the charged-current reaction and 52 live days reactor on and 34 live days reactor off for the neutral-current reaction. The measured neutral-current cross section is (5.0 +- 0.8) x 10-45cm2/anti ν/sub e/, consistent with the Weinberg-Salam model. The charged-current reaction cross section is (1.5 +- 0.4) x 10-45 cm2/ν/sub e/, in fair agreement with expectation. From the N.C. cross section a value of the square of the isovector axial-vector coupling constant is deduced to be β2 = 1.0 +- 0.15