After the completion of the gallium solar neutrino experiments at the Laboratori Nazionali del Gran Sasso (Gallex: 1991–1997; GNO: 1998–2003) we have retrospectively updated the Gallex results with ...the help of new technical data that were impossible to acquire for principle reasons before the completion of the low rate measurement phase (that is, before the end of the GNO solar runs). Subsequent high rate experiments have allowed the calibration of absolute internal counter efficiencies and of an advanced pulse shape analysis for counter background discrimination. The updated overall result for Gallex (only) is 73.4−7.3+7.1 SNU. This is 5.3% below the old value of 77.5−7.8+7.5 SNU (Gallex Collaboration, W. Hampel et al., 1999 1), with a substantially reduced error. A similar reduction is obtained from the reanalysis of the 51Cr neutrino source experiments of 1994/1995.
We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso for 13 months during 2011 and 2012. XENON100 features an ultralow ...electromagnetic background of (5.3 ± 0.6) × 10(-3) events/(keV(ee) × kg × day) in the energy region of interest. A blind analysis of 224.6 live days × 34 kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the predefined nuclear recoil energy range of 6.6-30.5 keV(nr) are consistent with the background expectation of (1.0 ± 0.2) events. A profile likelihood analysis using a 6.6-43.3 keV(nr) energy range sets the most stringent limit on the spin-independent elastic weakly interacting massive particle-nucleon scattering cross section for weakly interacting massive particle masses above 8 GeV/c(2), with a minimum of 2 × 10(-45) cm(2) at 55 GeV/c(2) and 90% confidence level.
We present new experimental constraints on the elastic, spin-dependent WIMP-nucleon cross section using recent data from the XENON100 experiment, operated in the Laboratori Nazionali del Gran Sasso ...in Italy. An analysis of 224.6 live days×34 kg of exposure acquired during 2011 and 2012 revealed no excess signal due to axial-vector WIMP interactions with 129Xe and 131Xe nuclei. This leads to the most stringent upper limits on WIMP-neutron cross sections for WIMP masses above 6 GeV/c², with a minimum cross section of 3.5×10(-40) cm² at a WIMP mass of 45 GeV/c², at 90% confidence level.
The XENON100 dark matter experiment uses liquid xenon in a time projection chamber (TPC) to measure xenon nuclear recoils resulting from the scattering of dark matter weakly interacting massive ...particles (WIMPs). In this paper, we report the observation of single-electron charge signals which are not related to WIMP interactions. These signals, which show the excellent sensitivity of the detector to small charge signals, are explained as being due to the photoionization of impurities in the liquid xenon and of the metal components inside the TPC. They are used as a unique calibration source to characterize the detector. We explain how we can infer crucial parameters for the XENON100 experiment: the secondary-scintillation gain, the extraction yield from the liquid to the gas phase and the electron drift velocity.
We report the complete GNO solar neutrino results for the measuring periods GNO III, GNO II, and GNO I. The result for GNO III (last 15 solar runs) is 54.3−9.3+9.9(stat)±2.3(syst)SNU(1σ) or ...54.3−9.6+10.2(incl. syst) SNU (1σ) with errors combined. The GNO experiment is now terminated after altogether 58 solar exposure runs that were performed between 20 May 1998 and 9 April 2003. The combined result for GNO (I+II+III) is 62.9−5.3+5.5(stat)±2.5(syst) SNU (1σ) or 62.9−5.9+6.0 SNU (1σ) with errors combined in quadrature. Overall, gallium based solar observations at LNGS (first in GALLEX, later in GNO) lasted from 14 May 1991 through 9 April 2003. The joint result from 123 runs in GNO and GALLEX is 69.3±5.5(incl. syst) SNU (1σ). The distribution of the individual run results is consistent with the hypothesis of a neutrino flux that is constant in time. Implications from the data in particle- and astrophysics are reiterated.
The radioisotope concentrations in stainless steel for the cryostat of the GERDA experiment at the Laboratori Nazionali del Gran Sasso (LNGS) have been measured. A total of 13 different stainless ...steel batches have been screened by low-level
γ
-ray spectrometry with germanium detectors located at two underground laboratories. The article reports the discovery of commonly available stainless steel with very low concentrations of primordial and cosmogenic radionuclides. The concentrations are in the range of 1
mBq/kg and below. Only the manmade
60Co-isotope is present in all samples with a higher concentration of around 19
mBq/kg. Further, deviations from secular equilibrium in the natural decay chains of U and Th have been observed in some cases.
We report the first GNO solar neutrino results for the measuring period GNO I, solar exposure time May 20, 1998 till January 12, 2000. In the present analysis, counting results for solar runs ...SR1–SR19 were used till April 4, 2000. With counting completed for all but the last 3 runs (SR17–SR19), the GNO I result is 65.8 ±
10.2
9.6 (stat.) ±
3.4
3.6 (syst.) SNU (1
σ) or 65.8 ±
10.7
10.2 (incl. syst.) SNU (1
σ) with errors combined. This may be compared to the result for Gallex (I–IV), which is 77.5 ±
7.6
7.8 (incl. syst.) SNU (1
σ). A combined result from both GNO I and Gallex (I–IV) together is 74.1 ±
6.7
6.8 (incl. syst.) SNU (1
σ).
The XENON100 experiment, installed underground at the Laboratori Nazionali del Gran Sasso, aims to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their ...elastic scattering off xenon nuclei. This paper presents a study on the nuclear recoil background of the experiment, taking into account neutron backgrounds from (α, n) reactions and spontaneous fission due to natural radioactivity in the detector and shield materials, as well as muon-induced neutrons. Based on Monte Carlo simulations and using measured radioactive contaminations of all detector components, we predict the nuclear recoil backgrounds for the WIMP search results published by the XENON100 experiment in 2011 and 2012, 0.11 events and 0.17 events, respectively, and conclude that they do not limit the sensitivity of the experiment.
We report the GALLEX solar neutrino results for the measuring period GALLEX IV, from 14 February 1996 until 23 January 1997. Counting for the GALLEX IV runs was completed on 19 June 1997. The GALLEX ...IV result from 12 solar runs is 118.4 ± 17.8 (stat.) ± 6.6 (sys.) SNU (1
σ). The combined result for GALLEX I+II+III+IV, which comprises 65 solar runs, is 77.5 ± 6.2
+4.3
−4.7(1
σ) SNU. The GALLEX experimental program to register solar neutrinos has now been completed. In April 1998, GALLEX was succeeded by a new project, the Gallium Neutrino Observatory (GNO), with newly defined motives and goals.
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