A. Salinas

Prospects of solar axion searches with crystal detectors

Abstract A calculation of the expected signal due to Primakoff coherent conversion of solar axions into photons via Bragg scattering in several crystal detectors is presented. The results are confronted with the experimental sensitivities of present and future experiments concluding that the sensitivity of crystal detectors does not challenge the globular cluster limit on the axion-photon coupling gaγγ. In particular, in the axion mass window ma ≳ 0.03 eV explored with this technique (not accessible at present by other methods), gaγγ might be constrained down to 10−9 GeV−1 (the recent helioseismological bound) provided that significant improvements in the parameters and performances of these detectors be achieved and large statistics accumulated. This bound should be considered as a minimal goal for the sensitivity of future crystal experiments. Consequently, finding a positive signal at this level of sensitivity would necessarily imply revisiting other more stringent astrophysical limits derived for the same range of ma values.

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.

Search for an annual modulation of dark-matter signals with a germanium spectrometer at the Sierra Grande Laboratory

Abstract Results of a search for dark-matter induced annual modulation using 830.5 kg·days of data collected at the Sierra Grande underground laboratory with a germanium detector are presented. The analysis of the data does not show any indication of seasonal effects.

Performances and prospects of the “ROSEBUD” dark matter search experiment

Abstract A cryogenic search for WIMP Dark Matter with small sapphire bolometers through the WIMP scattering off Al2O3 nuclei, the ROSEBUD (Rare Objects SEarch with Bolometers UndergrounD) experiment, is being installed in the Canfranc Underground Laboratory (Spain) at 2450 m water equivalent. The performances of the bolometers, the radioactive background expected from the measurement of the radiopurity of the ROSEBUD components and the estimated sensitivity of the experiment for low mass WIMP detection are presented.

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 status of the IGEX 76Ge double-beta decay experiment in 1997

Abstract The International Germanium Experiment (IGEX) has six detectors containing ∼ 90 fiducial moles of 76Ge. Data from 74.84 fiducial mole years yield a lower bound T 1 2 0ν > 0.8 × 10 25 y for neutrinoless double-beta decay of 76Ge.