J.H. Reeves

The IGEX Ge-76 neutrinoless double beta decay experiment: Prospects for next generation experiments

The International Germanium Experiment (IGEX) has analyzed 117 mole yr of 76Ge data from its isotopically enriched (86% 76Ge) germanium detectors. Applying pulse-shape discrimination (PSD) to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of 76Ge is:

Particle dark matter and solar axion searches with a small germanium detector at the Canfranc Underground Laboratory

T_{1/2}(0\nu)> 1.57 \times 10^{25}

Experimental Search for Solar Axions via Coherent Primakoff Conversion in a Germanium Spectrometer

yr (90% C.L.). This corresponds to an upper bound in the Majorana neutrino mass parameter,

Further reduction of radioactive backgrounds in ultrasensitive germanium spectrometers

, between 0.33 eV and 1.35 eV, depending on the choice of theoretical nuclear matrix elements used in the analysis.

New constraints on WIMPS from the Canfranc IGEX dark matter search

Abstract A small, natural abundance, germanium detector (COSME) has been operating recently at the Canfranc Underground Laboratory (Spanish Pyrenees) in improved conditions of shielding and overburden with respect to a previous operation of the same detector (Nucl. Instrum. Meth. A 321 (1992) 410; Phys. Rev. D 51 (1995) 1458). An exposure of 72.7 kg day in these conditions has at present a background improvement of about one order of magnitude compared to the former operation of the detector. These new data have been applied to a direct search for weakly interacting massive particles (WIMPs) and solar axions. New WIMP exclusion plots improving the current bounds for low masses are reported. The paper also presents a limit on the axion–photon coupling obtained from the analysis of the data looking for a Primakoff axion-to-photon conversion and Bragg scattering inside the crystal.

Recent results of the IGEX 76Ge double-beta decay experiment

Results are reported of an experimental search for the unique, rapidly varying temporal pattern of solar axions coherently converting into photons via the Primakoff effect in a single crystal germanium detector when axions are incident at a Bragg angle with a crystalline plane. The analysis of 1.94thinspthinspkgthinspyr of data from the 1thinspthinspkg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound by an axion-photon coupling of g{sub a{gamma}{gamma}}{lt}2.7{times}10{sup {minus}9} GeV{sup {minus}1} , independent of axion mass up to {approximately}1 keV . {copyright} {ital 1998} {ital The American Physical Society }

Pulse shape discrimination in the IGEX experiment

Two previous independent reports of 2v ββ decay by the ITEP-YPI Collaboration, T122v = (9±1) × 1020 yr (1σ), and the PNL-USC Collaboration, T122v = (1.12−0.26+0.48) × 1021 yr (2σ), are confirmed. A 0.25 kg Ge(Li) detector, isotopically enriched to 85% in 76Ge, was operated in the PNL-USC ultralow-background facility in the Homestake gold mine. Following a single correction to the data, a spectrum resembling that observed in the earlier PNL-USC experiment, with about the same intensity per 76Ge atom per year, was observed. The measured half-life is T122v = (9.2−0.4+0.7) × 1020 yr (2σ).

Achieving ultralow background in a germanium spectrometer

The radioactive background in two 1.1-kg Ge detectors was significantly reduced by material selection and careful control of fabrication of both the germanium crystals. The isotopes 57,58Co and 65Zn, formed cosmogenically in the crystals, were reduced by minimizing the time between the final between the final zone refinement, crystal growth, installation in the cryostat, and placement underground. An attempt was made to reduce the background from the decay of 68Ge in the detectors by deep mining the ore, rushing it through the refinement, crystal growing, and detector fabrication processes, and storing the germanium underground at all times it was not “in process”. Cosmogenically formed 54Mn, 59Fe, and 56,57,58,60Co in the cryostat were minimized by electroforming the cryostat parts. The ubiquitous background from primordial 40K in electronic components was virtually eliminated by selecting low-background components and by hiding the first-stage preamplifier behind 2.5 cm of 450-yr-old lead in one unit and special low-background lead in the other. Details of the procedures used are discussed.

The Majorana Project

Abstract The IGEX Collaboration enriched 76 Ge double-beta decay detectors are currently operating in the Canfranc Underground Laboratory with an overburden of 2450 m.w.e. A recent upgrade has made it possible to use them in a search for WIMPs. A new exclusion plot, σ (m), has been derived for WIMP-nucleon spin-independent interaction. To obtain this result, 30 days of data from one IGEX detector, which has an energy threshold E thr ∼4 keV, have been considered. These data improve the exclusion limits derived from other ionization (non-thermal) germanium detector experiments in the ∼50 GeV DAMA region, and show that with a moderate improvement of the background below 10 keV, the DAMA region may be tested with an additional 1 kg-year of exposure.