Heidelberg-Moscow Double Beta Research Articles

Massive neutrinos and dark energy

Recently, the Heidelberg-Moscow double beta decay experiment has claimed a detection for a neutrino mass with high significance. Here we consider the impact of this measurement on the determination of the dark energy equation of state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and other cosmological datasets we constrain the equation of state to − 1.67 w 1.05 at 95% c.l., ruling out a cosmological constant at more than 95% c.l.. Interestingly enough, coupled neutrino-dark energy models may be consistent with such equation of state. While future data are certainly needed for a confirmation of the controversial Heildelberg-Moscow claim, our result shows that future laboratory searches for neutrino masses may play a crucial role in the determination of the dark energy properties.

The impact of neutrino masses on the determination of dark energy properties

Recently, the Heidelberg-Moscow double beta decay experiment has claimed a detection for a neutrino mass with high significance. Here we consider the impact of this measurement on the determination of the dark energy equation of state. By combining the Heidelberg-Moscow result with the WMAP 3-years data and other cosmological datasets we constrain the equation of state to −1.67 < w < −1.05 at 95% c.l. Interestingly enough, coupled neutrino-dark energy models may be consistent with such equation of state. While future data are certainly needed for a confirmation of the controversial Heildelberg-Moscow claim, our result shows that future laboratory searches for neutrino masses may play a crucial role in the determination of the dark energy properties.

Can the Majorana Neutrino CP-Violating Phases be Restricted?

We reanalyze the constraints in neutrino masses and MNS lepton mixing parameters using the new data from the terrestrial (KamLAND) and astrophysical (WMAP) observations together with the Heidelberg–Moscow double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. We discuss the possibility of getting the bound for the Majorana CP-violating phase.

Search for cold and hot dark matter with the Heidelberg-Moscow experiment, HDMS, GENIUS and GENIUS-TF

The recent result [1] from the Heidelberg-Moscow double beta experiment allows neutrinos still to play an important role as hot dark matter in the Universe. HDMS has started in 2001 its search for cold dark matter (WIMPS), with a HPGe crystal of enriched 73 Ge [2]. Concerning hot dark matter, GENIUS will improve the present accuracy for the (effective) neutrino mass. At the same time GENIUS will extend the range of sensitivity in an unprecedented way to cover a wide range of the parameter space of SUSY parameters for neutralinos as cold dark matter. A GENIUS Test Facility in the Gran Sasso has been approved in 2001 and will come into operation by end of 2002. Finally some comments are given to some criticism of the result presented in [1,6].

CONSTRAINTS FROM NEUTRINOLESS DOUBLE BETA DECAY

We examine the constraints from the recent HEIDELBERG–MOSCOW double beta decay experiment. It leads us to the almost degenerate or inverse hierarchy neutrino mass scenario. In this scenario, we obtain possible upper bounds for the Majorana CP violating phase in the lepton sector by incorporating the data from the neutrino oscillation, the single beta decay experiments, and from the astrophysical observation. We also predict the neutrino mass that may be measurable in the future beta decay experiments.

Neutrinoless double beta decay in the supersymmetric seesaw model

Inspired by the recent HEIDELBERG-MOSCOW double beta decay experiment, we discuss the neutrinoless double beta decay in the supersymmetric seesaw model. Our numerical analysis indicates that we can naturally explain the data of the observed neutrinoless double beta decay, as well as that of the solar and atmospheric neutrino experiments with at least one Majorana-like sneutrino of middle energy scale in the model.

EVIDENCE FOR NEUTRINOLESS DOUBLE BETA DECAY

The data of the Heidelberg–Moscow double beta decay experiment for the measuring period August 1990–May 2000 (54.9813 kg y or 723.44 molyears), published recently, are analyzed using the potential of the Bayesian method for low counting rates. First evidence for neutrinoless double beta decay is observed giving first evidence for lepton number violation. The evidence for this decay mode is 97% (2.2σ) with the Bayesian method, and 99.8% c.l. (3.1σ) with the method recommended by the Particle Data Group. The half-life of the process is found with the Bayesian method to be [Formula: see text] (95% c.l.) with a best value of 1.5 × 1025 y . The deduced value of the effective neutrino mass is, with the nuclear matrix elements from Ref. 1, &lt;m&gt; = (0.11–0.56) eV (95% c.l.), with a best value of 0.39 eV. Uncertainties in the nuclear matrix elements may widen the range given for the effective neutrino mass by at most a factor 2. Our observation which at the same time means evidence that the neutrino is a Majorana particle, will be of fundamental importance for neutrino physics.

Search for new physics with neutrinoless doubel beta decay

Neutrinoless double decay (0νββ) is one of the most sensitive approaches to test particle physics beyond the standard model. During the last years, besides the most restrictive limit on the effective Majorana neutrino mass, the analysis of new contributions by the Heidelberg group led to bounds on left-right-symmetric models, leptoquarks and R-parity violating models competitive to recent accelerator limits, which are of special interest in view of the HERA anomaly at large Q 2 and χ. These new results deduced from the Heidelberg-Moscow double beta decay experiment are reviewed. Also an outlook on the future of double beta decay, the GENIUS proposal, is given.

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

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 〈 m ν 〉 ≤ 0.65 eV (90% C.L.) or 〈 m ν 〉 ≤ 0.50 eV (68% C. L.). For a superheavy neutrino, as it occurs, e. g., in seesaw models, we extract a limit of 〈 m H 〉 ≥ 5.1×10 7 GeV. These numbers are of importance in the context of presently discussed indications of physics beyond the Standard Model.

Status of the Heidelberg-Moscow ββ experiment with 76Ge

The status of the HEIDELBERG-MOSCOW double beta decay experiment using 16.9 kg of 86% enriched 76Ge is presented. From this material 12 kg are available in form of five grown crystals. Three detectors with a total mass of 6.02 kg are in regular operation in the GRAN SASSO underground laboratory. With a total 76Ge exposure of 91.63 mol·y we derive the following half life limits for the neutrinoless double beta (0τββ) decay: T 1 2 (0 + → 0 +) > 1.9·10 24 y and T 1 2 (0 + → 2 +) > 8.2·10 23 y with 90% C.L. In the transition to the ground state a stagnation of the half life limit in time is visible. By this limit a Majorana mass of the neutrinos larger than 1.1 eV is excluded. The background at 2 MeV is B = 0.3 counts/kg·y·keV for the total array. From the data taken with the second enriched detector a half life of T 1 2 = (1.42 ± 0.03 stat ± 0.13 syst )·10 21 y for the two neutrino double beta (2τββ) decay of 76Ge is extracted. This result represents with an 76Ge exposure of 19.3 mol·y the first high statistics measurement of this rare nuclear decay mode. From the same set of data a half life of 1.7·10 22 y is excluded for the neutrinoless decay with majoron emission (0τχββ), leading to an upper limit for the neutrino-majoron coupling of <g τχ < < 1.8·10 −4 with 90% C.L.

The HEIDELBERG-MOSCOW experiment: Searching for dark matter

First results on a dark matter search done by the HEIDELBERG-MOSCOW double beta decay experiment are presented. The experiment is running in the GRAN SASSO Underground Laboratory. A 2.9 kg ultra-low background HP-detector of enriched (86%) 76Ge, built to measure double beta decay, has been used to search for WIMPs. The measuring time is 60 days, corresponding to a statistical significance of 165 kg·d. Because of the extremely low background (0.067±0.002 counts/kg·dkeV) in the region 10–100 keV we obtain improved limits for the heavy WIMP cross sections. Perspectives of the experiment are discussed.

The Heidelberg-Moscow double beta decay experiment with enriched 76Ge: First results

Double beta decay probes beyond standard model physics. Status and perspectives of the HEIDELBERG-MOSCOW double beta decay experiment which is undertaken in the GRAN SASSO laboratory, are presented. Of the 16.9 kg of enriched (86%) 76Ge in hands of the cooperation, 9.6 kg have been converted into detectors (or crystals). At present 6 kg of detectors are in operation for data taking. The significance of the experiment at present is 1133 kg. d. Present limits for Ovββ decay to the g.s. and first excited state of 76Se, respectively, are: T 1 2 0v (0 + → 0 +) > 1.93 (3.21) × 10 24 y, and T 1 2 0v (0 + → 2 +) > 8.0 × 10 23 y (1.5 . 10 24 y) with 90% (68%) c.l. These values are the most stringent directly measured 0vββ half life limits known up to now. They correspond to an effective neutrino mass limit of <m v > < 1.1 (0.9) eV. For the neutrinoless decay with majoron emission a half life of 3.89 × 10 22 y can be excluded leading to an upper limit for the neutrino-majoron coupling of < g rx > < 1.10. 10 4 (90% c.l.). The background around 2 MeV is b=0.4 counts/kg y KeV for the total array, and 0.23 counts/kg y keV for the 2.9 kg detector. The experiment opens new perspectives for the investigation of exotic processes like electron decay, solar axions and dark matter. The new ββ-technology has found also application in high resolution balloon and satellite gamma-ray astronomy. Concerning the matrix elements for ββ decay a major step beyond the frequently used QRPA model has been made by applying the Operator Expansion Method (OEM).

The Heidelberg-Moscow double beta decay experiment with enriched 76Ge: First results

Abstract Status and perspectives of the HEIDELBERG-MOSCOW double beta decay experiment which is undertaken in the GRAN SASSO laboratory, are presented. Of the 16.9 kg of enriched (86%) 76Ge in hands of the cooperation, 6.5 kg have been converted into detectors. A 1 kg enriched detector was installed in July 1990, a 2.9 kg enriched detector, the largest HP Ge detector ever produced, with efficiency of 118% has been installed by september 1991. Present limits for 0νββ decay to the g.s. and first excited state of 76Se, respectively, are: T 1 2 0ν (0 + → 0 + ) > 1.1 (2.0) × 10 24 y, and T 1 2 0ν (0 + → 0 + ) > 2.2 (3.6) × 10 23 y with 90% (68%) c.1. These values are the most stringent directly measured 0νββ half life limits known up to now. They correspond to an effective neutrino mass limit of

The Heidelberg-Moscow double beta decay experiment with enriched 76Ge. First results

The status of the Heidelberg-Moscow ββ-experiment using isotopically enriched 76Ge is reported. The results of 14.8 mol yr (or 1.29 kg yr) of operation are presented. From these data a new half life time for the ββ0v-decay of 76Ge to the ground state of 76Se of T 1 2 1.4 (2.5) X 10 24 yr with 90% (68%) CL can be deduced. For a possible neutrinoless decay to the first excited state a half life of 4.3(8.2)X10 23 yr can be excluded with 90% (68%) CL.