Low energy neutrinos play important role in nuclear and astrophysical processes. Such neutrinos with energy below $\sim$100 MeV are able to scatter off the nucleus via elastic scattering. Neutrino-nucleus elastic scattering ($\nu A_{el}$) provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions. We present the detailed study and formulation of coherency effects, relate this to nuclear form factors and experimental cross-section ratios. The parameters chosen to quantify the coherency are universally applicable to different neutrino sources and target nuclei. We characterize how the energy dependence of the coherence factor leads to complementary among measurements at various neutrino sources with different targets. We also provide the constraints on coherency for the first generation discovery measurements of $\nu A_{el}$ with CsI target and theoretical expectations from Argon and Germanium target.

We report in situ neutron background measurements at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) by a hybrid neutron detector (HND) with a data size of 33.8 days under shielding configurations identical to those used during the neutrino physics data taking. The HND consists of BC-501A liquid and BC-702 phosphor powder scintillation neutron detectors, which are sensitive to both fast and thermal neutrons, respectively. Neutron-induced events for the two channels are identified and differentiated by pulse shape analysis, such that the backgrounds of both are simultaneously measured. The fast neutron fluxes are derived by an iterative unfolding algorithm. Neutron-induced backgrounds in the germanium detector under the same fluxes, due to both cosmic rays and ambient radioactivity, are derived and compared with the measurements. The results are valuable to background understanding of the neutrino data at the KSNL. In particular, neutron-induced background events due to ambient radioactivity as well as from reactor operation are negligible compared to intrinsic cosmogenic activity and ambient gamma activity. The detector concept and analysis procedures are applicable to neutron background characterization in similar rare-event experiments.

Constraints on couplings of several beyond-Standard-Model-physics scenarios, mediated by massive intermediate particles including ( 1) an extra Z-prime, ( 2) a new light spin-1 boson, and ( 3) a charged Higgs boson, are placed via the neutrino-electron scattering channel to test the Standard Model at a low energy-momentum transfer regime. Data on (nu) over bar (e) - e and nu(e) - e scattering from the TEXONO and LSND, respectively, are used. Upper bounds to coupling constants of the flavor-conserving and flavor-violating new light spin-1 boson and the charged Higgs boson with respect to different mediator masses are determined. The relevant parameter spaces are extended by allowing light mediators. New lower mass limits for extra Z-prime gauge boson models are also placed.

Neutrino-electron scattering is a purely leptonic fundamental interaction and therefore provides an important channel to test the Standard Model, especially at the low energy-momentum transfer regime. We derived constraints on neutrino nonstardard interaction couplings depending on model-independent approaches which are described by a four-Fermi pointlike interaction and the unparticle physics model with tensorial components. Data on (nu) over bar (e) - e and nu(e) - e scattering from the TEXONO and LSND experiments, respectively, are used. The upper limits and the allowed regions of scalar, pseudoscalar, and tensorial nonstandard interaction couplings of neutrinos are derived at 90% confidence level in both one-parameter and two-parameter analysis. New upper limits for tensorial unparticle physics coupling constants and mass parameters are also placed.

Germanium ionization detectors with sensitivities as low as 100 eVee (electron-equivalent energy) open new windows for studies on neutrino and dark matter physics. The relevant physics subjects are summarized. The detectors have to measure physics signals whose amplitude is comparable to that of pedestal electronic noise. To fully exploit this new detector technique, various experimental issues including quenching factors, energy reconstruction and calibration, signal triggering and selection as well as evaluation of their associated efficiencies have to be attended. The efforts and results of a research program to address these challenges are presented.