A. Demehin

Searching for dark matter with the enriched Ge detectors of the Heidelberg-Moscow ββ experiment

Abstract For the first time a search for dark matter with isotopically enriched material is done, by using the Ge detectors of the Heidelberg-Moscow experiment. A measuring time of 165.6 kg·d is used to set limits on the spin-independent cross section of weakly interacting massive particles (WIMPs). A background level of 0.102±0.005 events/(kg·d·keV) was achieved (average value between 11 keV and 30 keV). It was possible to extend the exclusion range for Dirac neutrino masses up to 4.7 TeV.

Sub-eV limit for the neutrino mass from 76Ge double beta decay by the HEIDELBERG-MOSCOW experiment

Abstract The HEIDELBERG-MOSCOW double beta decay experiment using HP germanium semiconductor detectors enriched in 76Ge is the first ββ experiment to penetrate into the sub-eV range. After a measuring time of 10.2 kg·a (117.0 mol·a) the half-life limit for 76Ge 0νββ decay is T 1 2 ≥ 5.6×10 24 a (90% C. L.) or T 1 2 ≥9.4×10 24 a (68% C.L.) which corresponds to an upper limit for the effective Majorana neutrino mass 〈mν〉 ≤ 0.65 eV (90% C.L.) or 〈mν〉 ≤ 0.50 eV (68% C. L.). For a superheavy neutrino, as it occurs, e. g., in seesaw models, we extract a limit of 〈mH〉 ≥ 5.1×107 GeV. These numbers are of importance in the context of presently discussed indications of physics beyond the Standard Model.

Background recognition in Ge detectors by pulse shape analysis

Abstract A method of event identification that distinguishes single and multiple-site events by determining the number of interactions in a high purity germanium detector is reported. The selectivity of the method has been experimentally verified.

Measurement of the ββ2ν decay of 76Ge

Abstract From the data taken with one of the enriched detectors of the Heidelberg-Moscow ββ experiment a half-life of T 1 2 2v = (1.42 ± 0.03 ( stat ) ± 0.13 ( syst )) × 10 12 yr for the two-neutrino double-beta ( ββ 2 ν ) decay of 76 Ge is derived. The 76 Ge exposure is 19.3 mol yr. This result represents the first high statistics measurement and probably the first undoubtable evidence of this extremely rare nuclear decay mode. The measured decay rate is in good agreement with the theoretical predictions.

Bounds on new Majoron models from the Heidelberg-Moscow experiment.

In recent years several new Majoron models were invented to avoid the shortcomings of the ordinary models while leading to observable decay rates in double {beta} experiments. We give the first experimental half-life bounds on double {beta} decays with new Majoron emission and derive bounds on the effective neutrino-Majoron couplings from the data of the {sup 76}Ge Heidelberg-Moscow experiment. While stringent half-life limits for all decay modes and the coupling constants of the ordinary models were obtained, small matrix elements and phase space integrals result in much weaker limits on the effective coupling constants of the new Majoron models. {copyright} {ital 1996 The American Physical Society.}

New experimental limits for electron decay and charge conservation

Abstract New experimental limits for the decay e− → γ + νe are reported. The lower limit for the half-life of this decay mode is T e 1 2 > 1.63 × 10 25 yr (68% CL). The data were collected for 3199 h by using one of the enriched germanium detectors of the Heidelberg-Moscow ββ Collaboration. This detector has an active volume of 591 cm3. This value is up to now the most stringent laboratory limit for this decay mode. Also charge nonconservation in nuclei is shortly discussed in the GaGe system using the data of gallium solar neutrino experiments.

New half life limits for the? ? 2v+0v decay of76Ge to the excited states of76Se from the Heidelberg-Moscow ?? experiment

Half life limits for theββ2v+0v decay of76Ge to excited states of76Se are deduced from the background spectrum of a passive shielding of zone refined germanium (139.5 kg). A special low-activity HPGe-detector (102 ccm) was mounted inside this shielding to search for the transition photons emitted in the decay of the excited states. The resulting limits for the (0+→21+ and the (0+→01+) transition are 6.3·1020 y (68%cl).

Recent double beta decay results

The status and recent results of second generation [beta][beta]-experiments using isotopically enriched source materials are described. These experiments are at present the most sensitive tools to distinguish Dirac from Majorana neutrinos. The at present most advanced experimental techniques, namely the use of high-resolution calorimetric detectors and of time projection chambers are compared. New limits on the Majorana neutrino mass as well as for the Majoron-neutrino coupling are presented.