Search

The p-type point-contact germanium detectors have been adopted for light dark matter WIMP searches and the studies of low energy neutrino physics. These detectors exhibit anomalous behavior to events located at the surface layer. The previous spectral shape method to identify these surface events from the bulk signals relies on spectral shape assumptions and the use of external calibration sources. We report an improved method in separating them by taking the ratios among different categories of in situ event samples as calibration sources. Data from CDEX-1 and TEXONO experiments are re-examined using the ratio method. Results are shown to be consistent with the spectral shape method., Comment: 29 pages, 16 figures

Germanium detectors with sub-keV sensitivities can probe low-mass WIMP Dark Matter. This experimental approach is pursued at Kuo-Sheng Neutrino Laboratory (KSNL) in Taiwan and at China Jinping Underground Laboratory (CJPL) in China via TEXONO and CDEX programs, respectively. The highlights of R&D efforts on point contact germanium detectors and in particular the differentiation of surface and bulk events by pulse shape analysis are described. The latest results on WIMP-nucleon scattering cross-sections are also presented. Some of the allowed parameter space implied by other experiments are probed and excluded.

We report the performance and characterization of a custom-built hybrid detector consisting of BC501A liquid scintillator for fast neutrons and BC702 scintillator for thermal neutrons. The calibration and the resolution of the BC501A liquid scintillator detector are performed. The event identification via Pulse Shape Discrimination (PSD) technique is developed in order to distinguish gamma, fast and thermal neutrons. Monte Carlo simulation packages are developed in GEANT4 to obtain actual neutron energy spectrum from the measured recoil spectrum. The developed methods are tested by reconstruction of 241AmBe(\alpha, n) neutron spectrum., Comment: 12 pages, 32 figures

Germanium detectors with sub-keV sensitivities open a window to search for low-mass WIMP dark matter. The latest limit on spin-independent couplings from the TEXONO experiment at the Kuo-Sheng Reactor Neutrino Laboratory is reported. Highlights of our R&D program, as well as the status and plans are discussed.

The article describes the research program towards an experiment to observe coherent scattering between neutrinos and the nucleus at the power reactor. The motivations of studying this process are surveyed. In particular, a threshold of 100–200 eV has been achieved with an ultra-low-energy germanium detector prototype. This detection capability at low energy can also be adapted for searches of Cold Dark Matter in the low-mass region as well as to enhance the sensitivities in the study of neutrino magnetic moments.

We report results of a search for light weakly interacting massive particle (WIMP) dark matter from the CDEX-1 experiment at the China Jinping Underground Laboratory (CJPL). Constraints on WIMP-nucleon spin-independent (SI) and spin-dependent (SD) couplings are derived with a physics threshold of 160 eVee, from an exposure of 737.1 kg-days. The SI and SD limits extend the lower reach of light WIMPs to 2 GeV and improve over our earlier bounds at WIMP mass less than 6 GeV., Comment: 10 pages, 10 figures

Finite neutrino magnetic moments are consequences of nonzero neutrino masses. The particle physics aspects of the neutrino electromagnetic interactions are reviewed. The astrophysical bounds and the results from recent direct experiments are reviewed, with emphasis on the reactor neutrino experiments. Future projects and prospects are surveyed.

The electromagnetic properties of neutrinos, which are either trivial or negligible in the context of the Standard Model, can probe new physics and have significant implications in astrophysics and cosmology. The current best direct limits on the neutrino millicharges and magnetic moments are both derived from data taken with germanium detectors with low thresholds at keV levels. In this paper, we discuss in detail a robust, ab initio method: the multiconfiguration relativistic random-phase approximation, that enables us to reliably understand the germanium detector response at the sub-keV level, where atomic many-body physics matters. By using existing data with sub-keV thresholds, limits on the reactor antineutrino's millicharge, magnetic moment, and charge radius squared are derived. The projected sensitivities for next-generation experiments are also given and discussed.

With the advent of detectors with sub-keV sensitivities, atomic ionization has been identified as a promising avenue to probe possible neutrino electromagnetic properties. The interaction cross-sections induced by millicharged neutrinos are evaluated with the ab-initio multi-configuration relativistic random-phase approximation. There is significant enhancement at atomic binding energies compared to that when the electrons are taken as free particles. Positive signals would distinctly manifest as peaks at specific energies with known intensity ratios. Selected reactor neutrino data with germanium detectors at analysis threshold as low as 300 eV are studied. No such signatures are observed, and a combined limit on the neutrino charge fraction of | \numq | < 1.0 X 10^{-12} at 90% confidence level is derived., 5 pages, 4 figures, 1 table ; Published Version as V2

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., Comment: 18 pages, 18 figures, 3 table; v3 -- Published Version

The CDEX Collaboration has been established for direct detection of light dark matter particles, using ultra-low energy threshold p-type point-contact germanium detectors, in China JinPing underground Laboratory (CJPL). The first 1 kg point-contact germanium detector with a sub-keV energy threshold has been tested in a passive shielding system located in CJPL. The outputs from both the point-contact p+ electrode and the outside n+ electrode make it possible to scan the lower energy range of less than 1 keV and at the same time to detect the higher energy range up to 3 MeV. The outputs from both p+ and n+ electrode may also provide a more powerful method for signal discrimination for dark matter experiment. Some key parameters, including energy resolution, dead time, decay times of internal X-rays, and system stability, have been tested and measured. The results show that the 1 kg point-contact germanium detector, together with its shielding system and electronics, can run smoothly with good performances. This detector system will be deployed for dark matter search experiments., 6 pages, 8 figures

Neutrino-electron scatterings are purely leptonic processes with robust standard model (SM) predictions. Their measurements can therefore provide constraints to physics beyond SM. The ${\overline{\ensuremath{\nu}}}_{\mathrm{e}}\ensuremath{-}\mathrm{e}$ data taken at the Kuo-Sheng Reactor Neutrino Laboratory were used to probe two scenarios: nonstandard neutrino interactions (NSI) and unparticle physics. New constraints were placed on the NSI parameters $({\ensuremath{\epsilon}}_{\mathrm{ee}}^{\mathrm{eL}},{\ensuremath{\epsilon}}_{\mathrm{ee}}^{\mathrm{eR}})$, $({\ensuremath{\epsilon}}_{\mathrm{e}\ensuremath{\mu}}^{\mathrm{eL}},{\ensuremath{\epsilon}}_{\mathrm{e}\ensuremath{\mu}}^{\mathrm{eR}})$, and $({\ensuremath{\epsilon}}_{\mathrm{e}\ensuremath{\tau}}^{\mathrm{eL}},{\ensuremath{\epsilon}}_{\mathrm{e}\ensuremath{\tau}}^{\mathrm{eR}})$ for the nonuniversal and flavor-changing channels, respectively, as well as to the coupling constants for scalar (${\ensuremath{\lambda}}_{0}$) and vector (${\ensuremath{\lambda}}_{1}$) unparticles to the neutrinos and electrons.

The {nu}{sub e}-e{sup -} 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 {nu}{sub e} flux of 6.4x10{sup 12} cm{sup -2} s{sup -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 kg-days of Reactor ON/OFF data, the standard model (SM) electroweak interaction was probed at the squared 4-momentum transfer range of Q{sup 2{approx}}3x10{sup -6} GeV{sup 2}. The ratio of experimental to SM cross sections of {xi}=[1.08{+-}0.21(stat){+-}0.16(sys)] was measured. Constraints on the electroweak parameters (g{sub V},g{sub A}) were placed, corresponding to a weak mixing angle measurement of sin{sup 2{theta}}{sub W}=0.251{+-}0.031(stat){+-}0.024(sys). Destructive interference in the SM {nu}{sub e}-e process was verified. Bounds on anomalous neutrino electromagnetic properties were placed: neutrino magnetic moment at {mu}{sub {nu}{sub e}}

An energy threshold of (220+-10) eV was achieved at an efficiency of 50% with a four-channel ultra-low-energy germanium detector each with an active mass of 5 g. This provides a unique probe to WIMP dark matter with mass below 10 GeV. With a data acquisition live time of 0.338 kg-day at the Kuo-Sheng Laboratory, constraints on WIMPs in the galactic halo were derived. The limits improve over previous results on both the spin-independent WIMP-nucleon and the spin-dependent WIMP-neutron cross-sections for WIMP mass between 3-6 GeV. Sensitivities for full-scale experiments are projected. This detector technique makes the unexplored sub-keV energy window accessible for new neutrino and dark matter experiments. Two appendices are included after Version-3 to address questions raised on trigger and selection efficiencies as well as other issues., Main Text: 5 pages, 1 table, 6 figures ; V1 -- spin-independent bounds ; V2 -- include spin-dependent bounds ; V3 -- Two appendices added to address questions raised ; V4 -- fixed technical errors

A search of axions produced in nuclear transitions was performed at the Kuo-Sheng Nuclear Power Station with a high-purity germanium detector of mass 1.06 kg at a distance of 28 m from the 2.9 GW reactor core. The expected experimental signatures were monoenergetic lines produced by their Primakoff or Compton conversions at the detector. Based on 459.0/96.3 days of reactor ON/OFF data, no evidence of axion emissions were observed and constraints on the couplings g{sub a{gamma}}{sub {gamma}} and g{sub aee} versus axion mass m{sub a} within the framework of invisible axion models were placed. The KSVZ and DFSZ models can be excluded for 10{sup 4} eV < or approx. m{sub a} < or approx. 10{sup 6} eV. Model-independent constraints on g{sub a{gamma}}{sub {gamma}}{center_dot}g{sub aNN}{sup 1}

A search of neutrino magnetic moments was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 $\cpd$ near threshold were achieved. Details of the reactor neutrino source, experimental hardware, background understanding and analysis methods are presented. Based on 570.7 and 127.8 days of Reactor ON and OFF data, respectively, at an average Reactor ON electron anti-neutrino flux of $\rm{6.4 \times 10^{12} cm^{-2} s^{-1}}$, the limit on the neutrino magnetic moments of $\rm{\munuebar < 7.4 \times 10^{-11} \mub}$ at 90% confidence level was derived. Indirect bounds on the $\nuebar$ radiative decay lifetimes were inferred., 16 pages, 15 figures, 9 tables

High flux of electron neutrinos($\nue$) is produced at nuclear power reactors through the decays of nuclei activated by neutron capture. Realistic simulation studies on the neutron transport and capture at the reactor core were performed. The production of $\chr51$ and $\fe55$ give rise to mono-energetic $\nue$'s at Q-values of 753 keV and 231 keV and fluxes of $8.3 \times 10^{-4}$ and $3.0 \times 10^{-4}$ $\nue$/fission, respectively. Using data from a germanium detector at the Kuo-Sheng Power Plant, we derived direct limits on the $\nue$ magnetic moment and the radiative lifetime of $\mu_{\nu} < 1.3 \times 10^{-8} ~ \mub$ and $\rm{\tau_{\nu} / m_{\nu} > 0.11 s / eV}$ at 90% confidence level (CL), respectively. Indirect bounds on $\rm{\tau_{\nu} / m_{\nu}^3}$ were also inferred. The $\nue$-flux can be enhanced by loading selected isotopes to the reactor core, and the potential applications and achievable statistical accuracies were examined. These include accurate cross-section measurements, studies of mixing angle $\theta_{13}$ and monitoring of plutonium production., Comment: 5 pages, 3 figures, 7 tables

The low energy part of the reactor neutrino spectra has not been experimentally measured. Its uncertainties limit the sensitivities in certain reactor neutrino experiments. The origin of these uncertainties are discussed, and the effects on measurements of neutrino interactions with electrons and nuclei are studied. Comparisons are made with existing results. In particular, the discrepancies between previous measurements with Standard Model expectations can be explained by an under-estimation of the low energy reactor neutrino spectra. To optimize the experimental sensitivities, measurements for $\nuebar$-e cross-sections should focus on events with large ($>$1.5 MeV) recoil energy while those for neutrino magnetic moment searches should be based on events $, Comment: 25 pages, 9 figures