Hans Volker Klapdor-Kleingrothaus

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

The evidence for the observation of 0ν beta beta decay: The identification of 0ν beta beta events from the full spectra.

T_{1/2}^{0\nu} = (0.8\hbox{--}18.3)\times 10^{25}~{\rm y}

Second-generation microscopic predictions of beta-decay half-lives of neutron-rich nuclei

(95% c.l.) with a best value of 1.5 × 1025y. The deduced value of the effective neutrino mass is, with the nuclear matrix elements from Ref. 1, = (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 evide...

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

In this brief review, a description of the observed evidence for neutrinoless double beta3–5 in the 76Ge experiment in Gran Sasso (Heidelberg–Moscow experiment) which has been operated with 11 kg enriched 76Ge detectors in the period 1990–2003, is provided. Two different methods of pulse shape analysis have been used to select potential 0νββ events from the γ background of the measured spectrum — a selection by a neuronal net approach,3,4,16 and a selection by a new method comparing measured pulses with a library of pulse shapes of point-like events calculated from simulation of the electric field distribution in the detectors (see Refs. 6–8 and 37). The latter method also allows spatial localization of measured events. Both methods lead to selections of events at Qββ with almost no γ-background. The observed line at Qββ is identified as a 0νββ signal. It has a confidence level of more than 6σ.

IMPLICATIONS OF OBSERVED NEUTRINOLESS DOUBLE BETA DECAY

Abstract Beta-decay half-lives for neutron-rich nuclei with 6 ≤ Z ≤ 108 between the line of β-stability and the neutron drip line have been calculated in a second-generation microscopic calculation using the proton-neutron quasiparticle random-phase approximation (QRPA) with a Gamow-Teller residual interaction. The accuracy of the predictions is considerably improved over that of earlier approaches based on the gross theory and the Tamm-Dancoff approximation (TDA).

Microscopic calculations of weak interaction rates of nuclei in stellar environment for A = 18 to 100

New results after 0.69 kg yr of measurement with an enriched

Two-neutrino double beta decay with operator expansion method

{}^{76}\mathrm{Ge}

ββ decay of 76Ge with renormalized effective interaction derived from Paris, Bonn and Reid potentials

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.

PROPOSAL FOR A NEW GE-SEMICONDUCTOR DARK MATTER DETECTOR

Recently a positive indication of the neutrinoless double beta decay has been announced. We study the implications of this result taking into consideration earlier results on atmospheric neutrinos and solar neutrinos. We also include in our discussions the recent results from SNO and K2K. We point out that on the confidence level given for the double beta signal, the neutrino mass matrices are now highly constrained. All models predicting Dirac masses are ruled out and leptogenesis becomes a natural choice. Only the degenerate and the inverted hierarchical solutions are allowed for the three-generation Majorana neutrinos. In both cases we find that the radiative corrections destabilize the solutions and the LOW, VO and Just So solutions of the solar neutrinos are ruled out. For the four-generation case only the inverted hierarchical scenario is allowed.

Measurement and QRPA calculation of the β-delayed neutron emission of 21,22N and 23,24O☆

Abstract: We report here the microscopic calculation of weak interaction rates in stellar matter for 709 nuclei with A = 18 to 100 using a generalized form of proton-neutron quasiparticle RPA model with separable Gamow-Teller forces. This is the first ever extensive microscopic calculation of weak rates calculated over a wide temperature-density grid which includes 107≤ T(K) ≤ 30 × 109 and 10 ≤ρ Ye (gcm−3) ≤ 1011, and over a larger mass range. Particle emission processes from excited states, previously ignored, are taken into account, and are found to significantly affect some β decay rates. The calculated capture and decay rates take into consideration the latest experimental energy levels and ft value compilations. Our calculation of electron capture and β-decay rates, in the fp-shell, show considerable differences with a recently reported shell model diagonalization approach calculation.