F. Petry

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.}

Investigation ofβ + β + andβ +/EC decay of106Cd

A low background scintillation detector with a CdWO4 crystal of 1.046 kg was used to search forβ+β+ andβ+/EC processes in106Cd. For the neutrinoless mode the limits T1/2(0νβ+β+)≥2.2·1019 y and T1/2(0νβ+/EC)≥5.5·1019 y were obtained with 90% C.L. For the possible two neutrino decay limits of T1/2(2νβ+β+)≥9.2·1017 y and T1/2(2νβ+/EC)≥2.6·1017 y have been determined with 99% C.L.

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.

Aspects of Dark Matter Direct Detection

The purpose of this article is to give a short introduction into the main aspects of a fast evolving field of research, namely the direct detection of possible dark matter particles [1, 2, 3], the so called WIMPs (Weakly Interacting Massive Particles).

Background identification by digital pulse shape analysis

Our work concerning digital pulse shape analysis consisted of two steps. A setup of two customary HP-germanium detectors was used to collect samples of pulses with different energies and well defined specifications. Those libraries were the basis for the development of a new approach to distinguish between pointlike and multiple scattered events. The new method was tested first in the low—level laboratory in Heidelberg. Than it was applied to one detector of the HEIDELBERG—MOSCOW ββ experiment. It was found that by identifying the multiple scattered events the background in the 0 vββ region can be reduced by a factor of five.