Measurement of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mover accent="true"><mml:mi>ν</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi mathvariant="normal">e</mml:mi></mml:msub></mml:math>-electron scattering cross section with a CsI(Tl) scintillating crystal array at the Kuo-Sheng nuclear power reactor

The ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}\ensuremath{-}{\mathrm{e}}^{\ensuremath{-}}$ elastic scattering cross section was measured with a CsI(Tl) scintillating crystal array having a total mass of 187 kg. The detector was exposed to an average reactor ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}$ flux of $6.4\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ at the Kuo-Sheng Nuclear Power Station. The experimental design, conceptual merits, detector hardware, data analysis, and background understanding of the experiment are presented. Using $29882/7369\text{ }\text{ }\mathrm{kg}$-days of Reactor ON/OFF data, the standard model (SM) electroweak interaction was probed at the squared 4-momentum transfer range of ${Q}^{2}\ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\text{ }\text{ }{\mathrm{GeV}}^{2}$. The ratio of experimental to SM cross sections of $\ensuremath{\xi}=[1.08\ifmmode\pm\else\textpm\fi{}0.21(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.16(\mathrm{sys})]$ was measured. Constraints on the electroweak parameters (${g}_{V},{g}_{A}$) were placed, corresponding to a weak mixing angle measurement of ${sin}^{2}{\ensuremath{\theta}}_{\mathrm{W}}=0.251\ifmmode\pm\else\textpm\fi{}0.031(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.024(\mathrm{sys})$. Destructive interference in the SM ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}\ensuremath{-}\mathrm{e}$ process was verified. Bounds on anomalous neutrino electromagnetic properties were placed: neutrino magnetic moment at ${\ensuremath{\mu}}_{{\overline{\ensuremath{\nu}}}_{\mathrm{e}}}&lt;2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\ensuremath{\mu}}_{\mathrm{B}}$ and the neutrino charge radius at $\ensuremath{-}2.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}32}\text{ }\text{ }{\mathrm{cm}}^{2}&lt;⟨{\mathrm{r}}_{{\overline{\ensuremath{\nu}}}_{\mathrm{e}}}^{2}⟩&lt;3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}32}\text{ }\text{ }{\mathrm{cm}}^{2}$, both at 90% confidence level.