H. Strecker

Latest results from the HEIDELBERG-MOSCOW double beta decay experiment

Abstract:New results for the double beta decay of 76Ge are presented. They are extracted from data obtained with the HEIDELBERG-MOSCOW experiment, which operates five enriched 76Ge detectors in an extreme low-level environment in the Gran Sasso underground laboratory. The two-neutrino-accompanied double beta decay is evaluated for the first time for all five detectors with a statistical significance of 47.7 kg y resulting in a half-life of T1/22ν = [1.55±0.01(stat)+0.19-0.15(syst)]×1021 y. The lower limit on the half-life of the 0νββ decay obtained with pulse shape analysis is T1/20ν > 1.9×1025(3.1×1025) y with 90% C.L. (68% C.L.) (with 35.5 kg y). This results in an upper limit of the effective Majorana-neutrino mass of 0.35 eV (0.27 eV) using the matrix elements of A. Staudt et al.s work (Europhys. Lett. 13, 31 (1990)). This is the most stringent limit at present from double beta decay. No evidence for a majoron-emitting decay mode is observed.

LIMITS ON THE MAJORANA NEUTRINO MASS IN THE 0.1 EV RANGE

The Heidelberg-Moscow experiment gives the most stringent limit on the Majorana neutrino mass. After 24 kg yr of data with pulse shape measurements, we set a lower limit on the half-life of the neutrinoless double beta decay in 76Ge of T_1/2 > 5.7 * 10^{25} yr at 90% C.L., thus excluding an effective Majorana neutrino mass greater than 0.2 eV. This allows to set strong constraints on degenerate neutrino mass models.

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.

The Heidelberg-Moscow experiment: improved sensitivity for 76Ge neutrinoless double beta decay

Abstract The Heidelberg-Moscow experiment operates five enriched 76Ge detectors with 10.96 kg active mass in the Gran Sasso underground laboratory. After 28.7 kg y of measurement with a counting rate between 2000 keV and 2080 keV of 0.20 ± 0.01 cts/kg y keV we receive a lower limit on the neutrinoless double beta decay of 76Ge of T 1 2 (0 + → 0 + ) > 1.1 × 10 25 y (90% C.L.). This restricts the Majorana neutrino mass to 0.46 eV. Recently we achieved a reduction in the background counting rate by a factor of 3–5 within the energy region of the neutrinoless double beta decay by recording the differentiated preamplifier pulse shapes and doing an off-line analysis to distinguish between pointlike and multiple scattered interactions.

New limits on dark-matter WIMPs from the Heidelberg-Moscow experiment

New results after 0.69 kg yr of measurement with an enriched

GENIUS-TF: A Test facility for the GENIUS project

{}^{76}\mathrm{Ge}

First results from the Heidelberg Dark Matter Search Experiment

detector of the Heidelberg-Moscow experiment with an active mass of 2.758 kg are presented. An energy threshold of 9 keV and a background level of 0.042 cts/(kg d keV) in the energy region between 15 keV and 40 keV was reached. The derived limits on the weakly interacting massive particles--nucleon cross section are the most stringent limits on spin-independent interactions obtained to date by using essentially raw data without background subtraction.

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

Abstract GENIUS is a proposal for a large scale detector of rare events. As a first step of the experiment, a small test version, the Genius Test-Facility will be built at the Laboratori Nazionali del Gran Sasso. With about 40 kg of natural Ge detectors operated in liquid nitrogen, GENIUS-TF could exclude (or directly confirm) the DAMA annual modulation seasonal modulation signature within about 2 yr of measurement using both, signal and signature of the claimed WIMP Dark Matter. The construction of the experiment has already been started, and four 2.5 kg germanium detectors with an extreme low threshold of 500 eV have been produced.

Investigation of the ββ decay of 116Cd into excited states of 116Sn

The Heidelberg Dark Matter Search Experiment (HDMS) is a new ionization Germanium experiment in a special design. Two concentric Ge crystals are housed by one cryostat system, the outer detector acting as an effective shield against multiple scattered photons for the inner crystal, which is the actual dark matter target. We present first results after successfully running the prototype detector for a period of about 15 months in the Gran Sasso Underground Laboratory. We analyze the results in terms of limits on WIMP-nucleon cross sections and present the status of the full scale experiment, which will be installed in Gran Sasso in the course of this year.

First results from the HDMS experiment in the final setup

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.