C. Sáenz

Theoretical and experimental investigation of cosmogenic radioisotope production in germanium

Abstract Rates were calculated for the cosmic-ray-induced production of 3 H, 54 Mn, 57 Ni, 57,58 Co, 65,67 Ga, 65 Zn, and 68 Ge in natural germanium using two experimental neutron spectra from the literature. Reaction excitation functions were computed with a nuclear spallation code. Experimental production rates of 54 Mn, 57,58 Co, 65 Zn, 67 Ga and 68 Ge were derived from background spectra of natural isotopic abundance germanium detectors. The rate for 57 Co was also derived from data taken with a detector fabricated from germanium isotopically enriched to 86% 76 Ge and ∼14% 74 Ge . The calculated and experimental data are in agreement within a factor of two and in many cases within 30%.

Filtering microphonics in dark matter germanium experiments

Abstract A technique for reducing the microphonic noise in a germanium spectrometer used in dark matter particles searches is described. Filtered energy spectra, corresponding to 48.5 kg day of data in a running experiment in the Canfranc tunnel are presented. Improvements of this filtering procedure with respect to the method of rejecting those events not distributed evenly in time are also discussed.

Searching for annual modulations of WIMPs with NaI scintillators

Abstract A search for cold dark matter has been carried out at the Canfranc Underground Laboratory (Spain) with 32.1 kg of sodium iodide scintillators during about two years of data taking. Bounds on WIMP masses and cross-sections for an exposure of 4613.6 kg day are presented, both for spin-independent and spin-dependent WIMP-matter interactions. The predicted annual modulation of the signal has been also investigated in 1342.8 kg day of data, getting exclusion plots stronger than those derived from the conventional method.

Recent results from the IGEX double-beta decay experiment

The International Germanium Experiment (IGEX) has six detectors, containing >90 fiducial moles of 76 Ge, operating underground. Data thus far yield T 1/2 2v = (1.1 ± 0.2) × 10 21 y and T 1/2 0v > 4.2 × 10 24 y(90% CL) if interpreted as a null experiment, or T 1/2 0v > 3.3 × 10 24 y(95% CL) in a more conservative case.

Dark matter searches with a germanium detector at the Canfranc tunnel

Abstract Results of a search for Cold Dark Matter particles in an experiment being carried out at the Canfranc Underground Laboratory are presented. Operating a natural isotopic abundance germanium detector of 234 grams for five thousand hours and using a simple method of filtering the microphonic noise, exclusion domains for masses and cross-sections of CDM particles are derived.

Searching for cold dark matter in the Southern Hemisphere. The experiment at Sierra Grande

Abstract An experimental search of distinctive signals of WIMPs is underway at the Sierra Grande mine (∼ 1000 m.w.e.) in Argentina with a natural germanium detector. The site and the experimental set-up are described. The results corresponding to an exposure of 302.4 kg day are presented in the customary form of σ(m) exclusion plots. The region in the WIMP-Ge cross-section versus WIMP mass plane ruled out by this experiment for heavy, non-relativistic neutrino-like Dirac particles scattering coherently off Ge nuclei through vector weak interactions corresponds to masses from 12 GeV up to about 1.7 TeV. The data taking is in progress with the purpose of looking for possible daily modulation effects in the Southern Hemisphere.

New experimental limits for the electron stability

Abstract A set of two natural abundance Ge detectors of 1.1 kg each, located in the Homestake mine, and one small, 0.253 kg, Ge detector operating in the Canfranc railway tunnel in Spain, have been used to obtain bounds on the stability of the electron against the decay modes e− → γνe and e − → ν e ν e ν e . The bounds on the mean lifes are τ(γνe) > 3.7(2.1) × 1025 yr, 68%(90%) CL and τ(ν e ν e ν e > 4.3(2.6) × 10 23 yr , 68%(90%) CL, which are at present the most stringent laboratory limits for these decays.

ANALYSIS OF AIRBORNE RADON IN AN ULTRA-LOW BACKGROUND EXPERIMENT

The contribution of 222Rn to the background in a low background experiment with a germanium detector has been estimated. We have also checked the efficacy of a standard radon cleaning system. The cleaning reduces the radon concentration two orders of magnitude with respect to the air in the laboratory. The residual 222Rn represents at most 12.5% of the background in the low energy region, a value low enough for the purpose of our experiment. A detailed study of the radioactive background is presented.

Status report on the International Germanium Experiment

Phase II detector fabrication for the International Germanium Experiment is awaiting resolution of technical details observed during Phase I. Measurements of fiducial volume, configuration of the tansistor-reset preamplifier stage, and sources of background are discussed. Cosmogenic {sup 7}Be is measured in germanium. Radium contamination in electroformed copper reported. The 2{nu} double- beta decay half-life of {sup 76}Ge measured with a Phase I detector is in reasonable agreement with previously reported values. No events are observed in the vicinity of the O{nu} double-beta decay energy.

The Lisbon-Zaragoza-Paris dark matter search

Abstract We present a status report on a pilot experiment to establish the feasibility of searching for evidence of weakly-interacting dark matter with an intrinsic metastable superconducting detector. The experiment, based on a device composed of 100 g of Sn microspheres ≤20 micron in diameter, is to be placed at the 2400 mwe depth of the Canfranc Underground Laboratory. It is designed to operate at 100 mK, yielding an event energy threshold ≤1.75 keV with a background rejection factor of 95%.