ν̄e− e− Scattering Cross-Section and Constraints on New Physics with a CsI(Tl) Crystal Array at the Kuo-Sheng Reactor Laboratory

The ν̄e− e− elastic scattering cross-section was measured with a CsI(Tl) scintillating crystal detector array with a total mass of 187 kg at the Kuo-Sheng Nuclear Power Station. The detectors were exposed to a reactor ν̄e flux of 6.4×1012 cm−2s−1 originated from a core with 2.9 GW thermal power. The physics motivations, conceptual design, detector hardware, data analysis and background understanding of the experiment are presented. Using 29882/7369 kg-days of Reactor ON/OFF data, the Standard Model (SM) of electroweak interaction was probed at the 4-momentum transfer range of ∼ 3×10−6 GeV2. A crosssection ratio of Rexpt = [1.08±0.21 (stat)±0.16 (sys)]×RSM was measured. Constraints on the electroweak parameters (gV,gA) were placed, corresponding to a weak mixing angle measurement of sinθW = 0.251±0.031 (stat)±0.024 (sys). The destructive interference in the SM ν̄e-e processes was verified with the value of RINT expt = −0.92± 0.30 (stat)± 0.24 (sys). Bounds on neutrino anomalous electromagnetic properties were placed: neutrino magnetic moment at μν̄e < 2.2× 10μB at 90% confidence level, and the neutrino charge radius at ⟨r2 ν̄e⟩= [0.61±1.30 (stat)±1.01 (sys)]×10 −32 cm2.