Z.Y. Zhou

Search of neutrino magnetic moments with a high-purity germanium detector at the Kuo-Sheng nuclear power station

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 kg{sup -1} keV{sup -1} day{sup -1} 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 antineutrino flux of 6.4x10{sup 12} cm{sup -2} s{sup -1}, the limit on the neutrino magnetic moments of {mu}{sub {nu}{sub e}}<7.4x10{sup -11}{mu}{sub B} at 90% confidence level was derived. Indirect bounds on the {nu}{sub e} radiative decay lifetimes were inferred.

Limit on the Electron Neutrino Magnetic Moment from the Kuo-Sheng Reactor Neutrino Experiment

A search of neutrino magnetic moment 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 kg(-1) keV(-1) day(-1) at 12-60 keV were achieved. Based on 4712 and 1250 h of reactor ON and OFF data, respectively, the limit on the neutrino magnetic moment of mu(nu;(e))<1.3x10(-10)mu(B) at 90% confidence level was derived. An indirect bound of the nu;(e) radiative lifetime of m(3)(nu)tau(nu)>2.8x10(18) eV(3) s can be inferred.

Limits on light weakly interacting massive particles from the CDEX-1 experiment with ap-type point-contact germanium detector at the China Jinping Underground Laboratory

We report results of a search for light Dark Matter WIMPs with CDEX-1 experiment at the China Jinping Underground Laboratory, based on 53.9 kg-days of data from a p-type point-contact germanium detector enclosed by a NaI(Tl) crystal scintillator as anti-Compton detector. The event rate and spectrum above the analysis threshold of 475 eVee are consistent with the understood background model. Part of the allowed regions for WIMP-nucleus coherent elastic scattering at WIMP mass of 6-20 GeV are probed and excluded. Independent of interaction channels, this result contradicts the interpretation that the anomalous excesses of the CoGeNT experiment are induced by Dark Matter, since identical detector techniques are used in both experiments.

Measurement of Nu(e)-bar -Electron Scattering Cross-Section with a CsI(Tl) Scintillating Crystal Array at the Kuo-Sheng Nuclear Power Reactor

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}} <3.3x10{sup -32} cm{sup 2}, both at 90% confidence level.

New limits on spin-independent and spin-dependent couplings of low-mass WIMP dark matter with a germanium detector at a threshold of 220 eV

An energy threshold of (220{+-}10) eV was achieved at an efficiency of 50% with a four-channel ultralow-energy germanium detector, each with an active mass of 5 g. This provides a unique probe to weakly interacting massive particles (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 spin-independent WIMP-nucleon and spin-dependent WIMP-neutron cross-sections for WIMP mass between 3 and 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.

A Search of Low-Mass WIMPs with p-type Point Contact Germanium Detector in the CDEX-1 Experiment

The CDEX-1 experiment conducted a search of low-mass (< 10 GeV/c2) Weakly Interacting Massive Particles (WIMPs) dark matter at the China Jinping Underground Laboratory using a p-type point-contact germanium detector with a fiducial mass of 915 g at a physics analysis threshold of 475 eVee. We report the hardware set-up, detector characterization, data acquisition and analysis procedures of this experiment. No excess of unidentified events are observed after subtraction of known background. Using 335.6 kg-days of data, exclusion constraints on the WIMP-nucleon spin-independent and spin-dependent couplings are derived.

Constraints on nonstandard neutrino interactions and unparticle physics with {nu}{sub e}-e{sup -} scattering at the Kuo-Sheng nuclear power reactor

(TEXONO Collaboration) 1 Institute of Physics, Academia Sinica, Taipei 11529, Taiwan. 2 Department of Physics, Middle East Technical University, Ankara 06531, Turkey. 3 Institute of High Energy Physics, Chinese Academy of Science, Beijing 100039, China. 4 Department of Engineering Physics, Tsinghua University, Beijing 100084, China. 5 Department of Nuclear Physics, Institute of Atomic Energy, Beijing 102413, China. 6 Department of Physics, Banaras Hindu University, Varanasi 221005, India. (Dated: August 10, 2010)

A CsI(Tl) scintillating crystal detector for the studies of low-energy neutrino interactions

Abstract Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Kuo-sheng Nuclear Power Station in Taiwan is being constructed for the studies of electron–neutrino scatterings and other keV–MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed.Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Nuclear Power Station II in Taiwan is being constructed for the studies of electron-neutrino scatterings and other keV−MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed. PACS Codes: 14.60.Pq; 29.40.Mc

Studies of prototype CsI(Tl) crystal scintillators for low-energy neutrino experiments

Crystal scintillators provide potential merits for the pursuit of low-energy low-background experiments. A CsI(Tl) scintillating crystal detector is being constructed to study low-energy neutrino physics at a nuclear reactor, while projects are underway to adopt this technique For Dark Matter searches. The choice of the geometrical parameters of the crystal modules. as well as the optimization of the readout scheme, are the results of an R&D program. Crystals 40 cm in length were developed. The detector requirements and the achieved performance of the prototypes are presented. Future prospects for this technique are discussed

Measurement of the intrinsic radiopurity of 137Cs/235U/238U/232Th in CsI(Tl) crystal scintillators

Abstract The inorganic crystal scintillator CsI(Tl) has been used for low energy neutrino and Dark Matter experiments, where the intrinsic radiopurity is an issue of major importance. Low-background data were taken with a CsI(Tl) crystal array at the Kuo-Sheng Reactor Neutrino Laboratory. The pulse shape discrimination capabilities of the crystal, as well as the temporal and spatial correlations of the events, provide powerful means of measuring the intrinsic radiopurity of 137 Cs as well as the 235 U, 238 U and 232 Th series. The event selection algorithms are described, with which the decay half-lives of 218 Po, 214 Po, 220 Rn, 216 Po and 212 Po were derived. The measurements of the contamination levels, their concentration gradients with the crystal growth axis, and the uniformity among different crystal samples, are reported. The radiopurity in the 238 U and 232 Th series are comparable to those of the best reported in other crystal scintillators. Significant improvements in measurement sensitivities were achieved, similar to those from dedicated massive liquid scintillator detector. This analysis also provides in situ measurements of the detector performance parameters, such as spatial resolution, quenching factors, and data acquisition dead time.