Search

In the mixed spin-scalar coupling approach the data from HDMS (Heidelberg Dark Matter Search) experiments performed in the years 1996, 1997, 2001–2003 both with natural Ge and with enriched 73Ge were simultaneously analyzed. This analysis together with a new procedure for background identification and subtraction from the measured 73Ge spectrum allowed us to obtain a significant (about one order of magnitude) improvement for the limits on the WIMP-neutron spin-dependent coupling. As a result, the HDMS experiment is now giving the most sensitive limits on the WIMP-neutron spin coupling for WIMP masses larger than 60–65 GeV/c 2.

A lower limit of > 1.22 × 10 26 yr (68% c.l.) has been determined for the mean life time of electron decay via the branch e − → γ + ν e . The limit was deduced from the spectra measured in the period 1995–2003 with the full set-up of 5 enriched 76Ge detectors of the Heidelberg–Moscow ββ experiment in the Gran Sasso underground laboratory. One of the detectors, and the setup 1 consisting of four detectors show an indication of a signal on a 1.4σ C.L. The best limit given by a single detector is 1.93 × 10 26 yr . The result is the by far sharpest limit obtained with Ge detectors. When comparing it with other limits, e.g. that from Borexino [H.O. Back, et al., Phys. Lett. B 525 (2002) 29] it may be essential to note that the present limit has been deduced from the raw data without any treatment of the background, and also, that the energy resolution in the present experiment is much larger than in the other most sensitive experiments. Combined with the best laboratory limit on the photon mass the present result gives the following restriction for charge nonconservation: ϵ e ν γ 0.86 × 10 −98 (68% c.l.) or 1.14 × 10 −97 (90% c.l.).

In this brief review, a description of the observed evidence for neutrinoless double beta3–5 in the 76 Ge experiment in Gran Sasso (Heidelberg–Moscow experiment) which has been operated with 11 kg enriched 76 Ge 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.

For the first time the expected pulse shapes to be observed for neutrinoless double beta events in a big 76 Ge detector have been calculated starting from their Monte Carlo calculated time history and spatial energy distribution. It is shown that with the spatial resolution of a large size Ge detector for the majority of 0νββ events it is not possible to differentiate between the contributions of different particle physics parameters entering into the 0νββ decay process — in the mass mechanism the effective neutrino mass and the right-handed weak current parameters λ, η. It is shown that on the other hand it is possible in a 76 Ge double beta decay experiment to reject a background of larger sizes (high multiplicity) gamma events by selecting low size (low multiplicity) events. First comparison of the theoretical ββ pulses to events from the line observed at3,4Qββ shows very good agreement. It is shown further that a rather good radial position determination of ββ events in the detector is possible. By the same type of calculation it is shown that use of the pulse shapes of the 1592 keV double escape line of the 2614 keV γ-transition from 228 Th for calibrating a neuronal net for search of events of neutrinoless double beta decay should be helpful.

The identification of signals of neutrinoless double beta decay is a question of extreme interest. Starting from the Monte Carlo calculated time history and spatial energy distribution of neutrinoless double beta events, for the first time the expected pulse shapes to be observed in a big 76 Ge detector have been calculated ‘ microscopically ’, by using the Poisson Superfish code for determination of the field distribution in the detector. It is shown, that for the majority of 0 ν β β events it is not possible to differentiate between the contributions of different particle physics parameters entering into the 0 ν β β decay process—in the mass mechanism the effective neutrino mass and the right-handed weak current parameters 〈 λ 〉 , 〈 η 〉 . It is shown, that on the other hand it is possible in a 76 Ge double beta decay experiment to reject a background of larger sizes (high multiplicity) gamma events by selecting low size (low multiplicity) events. First application of the theoretical ββ pulses to events from the line observed at Q β β [H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, et al., Phys. Lett. B 586 (2004) 198; H.V. Klapdor-Kleingrothaus, A. Dietz, I.V. Krivosheina, et al., Nucl. Instrum. Methods A 522 (2004) 371] shows very good agreement. It is shown further, and confirmed by measurements with a collimated source, that a rather good radial position determination of ββ events in the detector is possible. By the same type of calculation it is shown that use of the pulse shapes of the 1592 keV double escape line of the 2614 keV γ -transition from 228 Th for calibrating a neuronal net for search of events of neutrinoless double beta decay can be helpful.

In this review for the first time a theoretical description of the tracks of events of nuclear double beta decay in a large Ge detector is presented. It is obvious that in principle the shapes and sizes of these tracks — and the corresponding time structure of pulses — depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, and nuclear matrix elements. The knowledge of this dependence is of importance, since the key to probe the existence of 0νββ decay beyond observation of a signal at the Q value of the process, Qββ, is the discrimination of ββ events from background γ events (or other events), in almost any double beta decay experiment (see Refs. 2 and 3). In this review Monte-Carlo simulations of tracks of neutrino-accompanied (2νββ) and neutrinoless double beta decay (0νββ) events, and of various kinds of background processes such as multiple and other γ interactions are reported for a large Ge detector. The time history of the evolution of the individual events is followed and the sizes of the events (volumes in the detector inside which the energy of the event is released) are investigated. Effects of the angular correlations of the two electrons in ββ decay, which again depend on the above nuclear and (for 0νββ decay) particle physics parameters, are taken into account and have been calculated for this purpose for the first time on basis of the experimental half-life of 76 Ge and of realistic nuclear matrix elements. It is shown for ββ decay of 76 Ge , that 0νββ events are to a large extent separable from Compton scattering of γ events of the same energy, while double escape peaks of γ-lines show very similar behavior as 0νββ events, and in that sense can be useful for corresponding "calibration" of pulse shapes of the detector. The possibility to distinguish 0νββ events from γ events is found to be essentially independent of the particle physics parameters of the 0νββ process. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters 〈mν〉, 〈λ〉, 〈η〉. It is suggested, that the strategy in future 0νββ research should be, to combine confirmation of the HEIDELBERG-MOSCOW result with determination of the mechanism of the dominating decay, instead of repeating earlier experiments or ideas. The future experiment thus should not use 76 Ge or 136 Xe , but instead 124 Xe .

The sizes of tracks of events of neutrinoless double beta decay in a germanium detector depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, etc., and nuclear matrix elements. The knowledge of this dependence is of importance, since the key to probe the existence of 0 ν β β decay beyond observation of a signal at the Q value of the process, Q β β , is the discrimination of ββ events from background γ events (or other events), in almost any double beta decay experiment (see [H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, et al., Phys. Lett. B 586 (2004) 198; H.V. Klapdor-Kleingrothaus, A. Dietz, I.V. Krivosheina, et al., Nucl. Instrum. Methods A 522 (2004) 371]). In this Letter for the first time Monte Carlo simulations of neutrino-accompanied ( 2 ν β β ) and neutrinoless double beta decay ( 0 ν β β ) events, and of various kinds of background processes such as multiple and other γ interactions are reported for a Ge detector. The time history of the evolution of the individual events is followed and a systematic study has been performed of the sizes of the events (volumes in the detector inside which the energy of the event is released which determine the observed signals). Effects of the angular correlations of the two electrons in ββ decay, which again depend on the above nuclear and (for 0 ν β β decay) particle physics parameters, are taken into account and have been calculated for this purpose for 76Ge for the first time on basis of the experimental half-life and of realistic nuclear matrix elements. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters 〈 m ν 〉 , 〈 λ 〉 , 〈 η 〉 .

After the installation of the first four naked high purity Germanium detectors in liquid nitrogen in the GRAN SASSO Underground Laboratory in the GENIUS-Test-Facility (GENIUS-TF-I) on May 5, 2003, an improved setup GENIUS-TF-II with now six detectors (15 kg), has been installed on October 14, 2004. This is the only setup existing worldwide until now (April 2005) which applies this novel technique aiming at extreme background reduction in search for rare decays underground. The GENIUS-TF experiment, aims to search for the annual modulation of the Dark Matter signal. The HDMS (Heidelberg Dark Matter Search experiment) is the only experiment worldwide, operating an enriched 73Ge detector and is looking for spin-dependent WIMP-neutron interactions. Results for the measurement Febr. 2001–July 2003 are presented. They improve the best existing present limits for low WIMP masses.

The HEIDELBERG-MOSCOW experiment operating 11 kg of enriched 76Ge in the GRAN SASSO Underground Laboratory, is one of the long-running underground experiments. It is the most sensitive double beta decay experiment since more than ten years. The measurement, and the analysis of the data taken from 2 August 1990-20 May 2003, which has been performed in the second half of 2003, is presented here. The duty cycle of the experiment was ∼80%, the collected statistics is 71.7kgy. The background achieved in the energy region of the Q value for double beta decay is O.11events/kgykeV. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to a 4.2 σ level. Fundamental consequences of this first evidence for neutrinoless double beta decay is that total lepton number is not conserved, and further, that the neutrino is a Majorana particle, and further that only a degenerate neutrino mass model is allowed. The effective neutrino mass deduced is (0.2-0.6)eV.

The HDMS (Heidelberg dark matter search) setup at LNGS, operates the first enriched 73Ge detector worldwide, and looks for spin-dependent WIMP-nucleon coupling at the Gran Sasso Underground Laboratory. The data collected from February 2001 to July 2003 (423.18 d, corresponding to 85.48 kg d) are presented. The results improve the best present existing limits on the WIMP-neutron spin-dependent cross section (obtained from 129Xe) for low WIMP masses.

Nuclear weak interaction rates for fp- and fpg-shell nuclei in stellar matter and the associated energy losses are calculated using a modified form of proton–neutron quasiparticle random phase approximation model with separable Gamow–Teller forces. The stellar weak rates are calculated over a wide range of densities (10 ⩽ ρYe (g cm−3) ⩽ 1011) and temperatures (107 ⩽ T (K) ⩽ 30 × 109). We also calculate the probability of particle emission processes in stellar environment. We present an extensive compilation of weak interaction rates in stellar matter calculated over a wide temperature–density grid and over a large mass range. The calculated capture and decay rates take into consideration the latest compilations of experimental energy levels and ft values. This paper is a follow up of our calculations introduced earlier [Eur. Phys. J. A 5 (1999) 337]. We have calculated stellar weak interaction rates for a total of 650 nuclei in the mass range A = 40–100. These also include many important neutron-rich nuclei which play an important role in the evolution process of stellar collapse.

GENIUS-TF (Nucl. Instr. and Meth. A 511 (2003) 341; Nucl. Instr. and Meth. A 481 (2002) 149.) is a test-facility for the GENIUS project (GENIUS-Proposal, 20 November 1997; Z. Phys. A 359 (1997) 351; CERN Courier, November 1997, 16; J. Phys. G 24 (1998) 483; Z. Phys. A 359 (1997) 361; in: H.V. Klapdor-Kleingrothaus, H. Pas. (Eds.), First International Conference on Particle Physics Beyond the Standard Model, Castle Ringberg, Germany, 8–14 June 1997, IOP Bristol (1998) 485 and in Int. J. Mod. Phys. A 13 (1998) 3953; in: H.V. Klapdor-Kleingrothaus, I.V. Krivosheina (Eds.), Proceedings of the Second International Conference on Particle Physics Beyond the Standard Model BEYOND’ 99, Castle Ringberg, Germany 6–12 June 1999, IOP Bristol (2000) 915), a proposed large scale underground observatory for rare events which is based on operation of naked germanium detectors in liquid nitrogen for an extreme background reduction. Operation of naked Ge crystals in liquid nitrogen has been applied routinely already for more than 20 years by the CANBERRA Company for technical functions tests (CANBERRA Company, private communication, 5 March 2004.), but it never had found entrance into basic research. Only in 1997 first tests of application of this method for nuclear spectroscopy have been performed, successfully, in Heidelberg (Klapdor-Kleingrothaus et al., 1997, 1998; J. Hellmig and H.V. Klapdor-Kleingrothaus, 1997). On May 5, 2003 the first four naked high-purity germanium detectors (total mass 10.52 kg ) were installed in liquid nitrogen in the GENIUS Test Facility at the Gran Sasso underground laboratory. Since then the experiment has been running continuously, testing for the first time the novel technique in an underground laboratory and for a long-lasting period. In this work, we present the first analysis of the GENIUS-TF background after the completion of the external shielding, which took place in December 2003. We focus especially on the background coming from 222 Rn daughters. This is found to be at present by a factor of 200 higher than expected from simulation. It is still compatible with the scientific goal of GENIUS-TF, namely to search for cold dark matter by the modulation signal, but on the present level would cause serious problems for a full GENIUS—like experiment using liquid nitrogen.

Data acquisition in a long-running underground experiment has its specific experimental challenges, concerning data acquisition, stability of the experiment and background reduction. These problems are addressed here for the HEIDELBERG–MOSCOW experiment, which collected data in the period August 1990–May 2003. The measurement and the analysis of the data are presented. The duty cycle of the experiment was ∼80%, and the collected statistics is 71.7 kg year. The background achieved in the energy region of the Q value for double beta decay is 0.11 events / kg year keV . The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to a 4σ level.

Based on the Monte-Carlo package G eant 4 a new simulation of the complete background spectrum of the HEIDELBERG-MOSCOW experiment which operates five enriched 76 Ge detectors in a low background environment in the Gran Sasso underground laboratory was performed. The resulting background model is used to evaluate the signal of the two neutrino accompanied double beta decay with a statistical significance of 41.57 kg year resulting in a half-life of T1/22ν=(1.74±0.01(stat)−0.16+0.18(syst))×1021 years. Using G eant 4 a simulation of elastic and inelastic neutron reactions has been performed for the first time and is used to estimate the contribution of the neutron flux in the Gran Sasso underground laboratory to the experimental spectrum. The composition of the background in the energy range from 2000 to 2100 keV around the Q value for neutrinoless double beta decay is discussed in some detail.

Observation of the neutrinoless double beta decay ($\0n$) has established that there is lepton number violation in nature and the neutrino masses are Majorana in nature. It also gives the absolute mass of the neutrinos and discriminates between different models of neutrino masses. The allowed amount of lepton number violation puts severe constraints on some possible new physics beyond the standard model. The recent results from WMAP are consistent with the consequences of the neutrinoless double beta decay. They improve some of these constraints very marginally, which we shall summarise here. We mention the new physics which are not affected by WMAP and could make both these limits from the neutrinoless double beta decay and WMAP consistent., Comment: 15 pages latex with 1 figure

The first four naked high purity Germanium detectors were installed successfully in liquid nitrogen in the GENIUS-Test-Facility (GENIUS-TF) in the GRAN SASSO Underground Laboratory on May 5, 2003. This is the first time ever that this novel technique aiming at extreme background reduction in search for rare decays is going to be tested underground. First operational parameters are presented.

In this work we present the results obtained measuring the 214Bi spectrum from a 226Ra source with a high purity germanium detector. Our attention was mostly focused on the energy region around the Q-value of 76Ge neutrinoless double-beta decay (2039.006 keV). The results of this measurement are strongly related to the first indication for the neutrinoless double beta decay of 76Ge, given by a recent analysis \cite{Evidence,KK02-PN,KK02-Found,KK-BigArt02} of the data collected during ten years of measurements from the HEIDELBERG-MOSCOW experiment.

The background in the region of the Q-value for neutrinoless double beta decay of 76Ge has been investigated by different methods: Simulation with GEANT 4 of the HEIDELBERG-MOSCOW experiment, analysis of other Ge double beta experiments.Statistical features of the analysis at very low count rates are discussed.

The double-beta decay matrix elements and half-lives for 106Cd are computed with the second quasi random phase approximation (SQRPA) method and using two single-particle (s.p.) bases. For the neutrino-emitting decay modes the two-positron emission (\(\beta^+\beta^+\)), the positron emission/electron capture (\(\beta^+\)/EC) and the double electron capture (EC/EC) processes are treated. It was found that the nuclear matrix elements (NME) display a strong dependence on the strength of the particle-particle interaction and an important contribution to the decay amplitude is coming from the 1+ ground state of the intermediate nucleus 106Ag. Their values depend weakly on the s.p. basis used. For both bases the deviations from the Ikeda sum rule are only within 2-3%. We got half-lives for the \(\beta^+\)/EC of the order of \(\sim 10^{21} \) y which is not far from the actual experimental limits. For the neutrinoless \(\beta^+\beta^+\) and \(\beta^+\)/EC decay modes the NME relevant both for the mass mechanism and the right-handed (RH) currents were calculated. They are found to be slightly larger than those obtained in our previous calculations (M. Hirsch, K. Muto, T. Oda, H.V. Klapdor-Kleingrothaus, Z. Phys. A 334, 151 (1994)). Using the value of the neutrino mass parameter extracted from the recently reported first experimental evidence of the neutrinoless decay mode (i.e. 0.39 eV) (H.V. Klapdor-Kleingrothaus, A. Dietz, H.I. Harney, I.V. Krivosheina, hep-ph/0201231; Mod. Phys. Lett. A 16, 2409 (2001); H.V. Klapdor-Kleingrothaus, A. Dietz, I.V. Krivosheina, Part. Nucl. Lett. 110, 57 (2002); Found. Phys. 32, 1181 (2002)), we got half-lives of \(\sim 10^{28}\) y and 1027 y, for the \(0\nu\beta^+\beta^+\) and \(0\nu\beta^+\)/EC processes, respectively. An experimental investigation of these decays could be useful for testing the importance of the right-handed current mechanism to the occurrence of neutrinoless \(\beta\beta\) decay.

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].

In this paper we will present the first results of applying a digital processing technology in low-level gamma spectroscopy with HPGE detectors. An experimental gamma spectrometer using Flash ADC module is built and tested. The test system is now under development and shows major advantages over the traditional analog technologies. It will be installed for the GENIUS-TF and GENIUS projects in Gran-Sasso in early 2003.

The new project GENIUS will cover a wide range of the parameter space of predictions of SUSY for neutralinos as cold dark matter. Further it has the potential to be a real-time detector for low-energy (pp and 7Be) solar neutrinos. A GENIUS Test Facility has been funded and will come into operation by early 2003.

Double beta decay is indispensable to solve the question of the neutrino mass matrix together with $\nu$ oscillation experiments. Recent analysis of the most sensitive experiment since nine years - the HEIDELBERG-MOSCOW experiment in Gran-Sasso - yields a first indication for the neutrinoless decay mode. This result is the first evidence for lepton number violation and proves the neutrino to be a Majorana particle. We give the present status of the analysis in this report. It excludes several of the neutrino mass scenarios allowed from present neutrino oscillation experiments - only degenerate scenarios and those with inverse mass hierarchy survive. This result allows neutrinos to still play an important role as dark matter in the Universe. To improve the accuracy of the present result, considerably enlarged experiments are required, such as GENIUS. A GENIUS Test Facility has been funded and will come into operation by early 2003.

Double-beta decay is indispensable to solve the question of the neutrino mass matrix together with ν oscillation experiments. Recent analysis of the most sensitive experiment in the last eight years—the Heidelberg-Moscow experiment in Gran Sasso—yields evidence for the neutrinoless decay mode at a 97% C.L. This result is the first indication for lepton number violation and for the neutrino to be a Majorana particle. We give the present status of the analysis in these proceedings. It excludes several of the neutrino mass scenarios allowed from present neutrino oscillation experiments—essentially only degenerate and partially degenerate mass scenarios survive. To improve the present result, considerably enlarged experiments are required, such as GENIUS. A GENIUS Test Facility has just been funded and will come into operation by the end of 2002.

Dark matter is at present one of the most exciting field of particle physics and cosmology. We review the status of undergound experiments looking for cold and hot dark matter.

Detection of the recoil energy deposited by a weakly interacting massive particle (WIMP) scattering off a nucleus or of the neutrinoless double beta decay signature in a `naked' (natural or enriched) Ge crystal immersed in liquid nitrogen provides a new, yet simple implementation of a well know technology to the fields of direct dark matter and double beta decay searches. We show that an array with a total mass of 40 kg of natural Ge and 11 kg of enriched 76 Ge detectors operated in liquid nitrogen in a compact setup could yield important physics results by directly looking for a WIMP signature and testing the Majorana neutrino mass down to 0.1 eV. The method could be easily extended to much larger masses and, by increasing the amount of liquid nitrogen surrounding the detectors, to much lower backgrounds.

The present experimental status in the search for neutrinoless double beta decay is reviewed, with emphasis on the first indication for neutrinoless double beta decay found in the Heidelberg-Moscow experiment, giving first evidence for lepton number violation and a Majorana nature of the neutrinos. Future perspectives of the field are briefly outlined.

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 these 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., Comment: 16 pages, 2 postscript figures

A systematic study of the two-neutrino and neutrinoless double-beta decay matrix elements (ME) for the nuclei with A =76, 82, 96, 100, 116, 128, 130 and 136 is done. The calculations are performed with four different quasi random phase approximation (QRPA)-based methods, i.e. the proton–neutron QRPA (pnQRPA), the renormalized proton–neutron QRPA (pnRQRPA), the full-RQRPA and the second-QRPA (SQRPA). First we checked the conservation of the Ikeda sum rule (ISR) and found that it is fulfilled with a good accuracy for the SQRPA, while for the pnRQRPA and full-RQRPA the deviations are up to 17%. Then, we studied the dependence of the ME on the single-particle (s.p.) basis. For that we performed the calculations using the same set of parameters and two different s.p. basis. For the two-neutrino decay mode the ME manifest generally the largest sensitivity to the choice of the basis when they are calculated with the pnQRPA, while the smallest sensitivity is got with the SQRPA. For all the methods the largest differences between the results were found for 128,130 Te and 136 Xe. For the neutrinoless decay mode the ME display generally a stronger dependence on the basis than for the two-neutrino decay mode, when they are calculated with the pnQRPA, RQRPA and full-RQRPA, while for SQRPA differences in the results are within 30%. A better stability against the change of the s.p. basis used and a good fulfillment of the ISR allow to reduce the uncertainties in the values of the neutrinoless ME predicted by the QRPA-based methods to about 50% from their magnitude. Further, we fixed the values of g pp from the two-neutrino calculations and according to recent experimental data, and then we used them to compute the ME for the neutrinoless decay mode. Taking the most recent experimental limits for the neutrinoless half-lives, we deduce new upper limits for the neutrino mass parameter. Finally, there are estimated, for each nucleus, scales for the neutrinoless double-beta decay half-lives that the experiments should reach for exploring neutrino masses around 0.1 eV. This might guide the experimentalists in planning their setups.

A method that discriminates between single- and multiple-site interactions in germanium detectors was developed. For this purpose the output of customary charge-sensitive preamplifiers was differentiated with 10–20 ns sampled with 250 MHz and analyzed off-line. Multiple-site interactions were measured in the 1621 keV photo peak and single-site events in the 1592 keV double escape line of 208 Tl. One single parameter describing the broadness of the charge pulse maximum is sufficient to achieve 80% detection efficiencies for both the interaction types, over a wide energy range. As examples, employment of the method in the Heidelberg–Moscow experiment resulted in the consistent half-life of two neutrino double beta decay and the reduction of the background by a factor of three in searches for the neutrinoless double beta decay. Identification of single Compton scattered events improved the minimal detectable activity of a 25% efficiency detector by a factor of two.

We study the experimental constraints on theories, where the equivalence principle is violated by dilaton-exchange contributions to the usual graviton-exchange gravity. We point out that in this case it is not possible to have any CPT violation and hence there is no constraint from the CPT violating measurements in the $K-$system. The most stringent bound is obtained from the $K_L - K_S$ mass difference. In contrast, neither neutrino oscillation experiments nor neutrinoless double beta decay imply significant constraints., 7 pages

The potential of the GENIUS (GErmanium in liquid NItrogen Underground Setup) experiment, proposed as the successor of the Heidelberg-Moscow experiment, for the search for neutrinoless double-beta decay, the direct search for neutralino Cold Dark Matter, and for other physics beyond the Standard Model will be presented. The current status of the Heidelberg-Moscow experiment will be reviewed.

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., 6 pages (latex) including 3 postscript figures and 2 tables

We present a new Germanium Dark Matter Experiment. It consists of two HPGe-Detectors which are run in a unique configuration. The anticoincidence between the two detectors will further reduce the background that we achieve now in the Heidelberg-Moscow-Experiment and will allow to improve WIMP cross section limits to a level comparable to planned cryogenic experiments. This should also allow to test recently claimed positive evidence for dark matter by the DAMA experiment. We show first detector performances from the test period in the Heidelberg Low Level Laboratory and give a preliminary estimation for the background reduction efficiency. The HDMS experiment in being built up now in the Gran Sasso Underground Laboratory and will start taking data by the end of this year. For a substantial improvement of the WIMP-nucleon cross section limits, future dark matter experiments will have to be either massive direction-sensitive detectors or massive ton-scale detectors with almost zero background. A proposal for a high mass (1 ton) Ge experiment with a much further reduced background is the Heidelberg GENIUS experiment. GENIUS will be able to give a WIMP limit of the order 0.02 counts/day/kg and additionally to look for the annual modulation WIMP-signature by using raw data without subtraction.

Nuclear recoil measurements with high-purity Germanium detectors are very promising to directly detect dark matter candidates. The main background sources in such experiments are natural radioactivity and microphonic noise. Digital pulse shape analysis is an encouraging approach to reduce the background originating from the latter. To study the pulse shapes of nuclear recoil events we performed a neutron scattering experiment, which covered the ionization energy range from 20 to 80 keV. We have measured ionization efficiencies as well and found an excellent agreement with the theory of Lindhard. In a further experiment we measured pulse shapes of a radioactive gamma-source and found no difference to nuclear recoil pulse shapes. Pulse shapes originating from microphonics of a HPGe-detector are presented for the first time. A microphonic noise suppression method, crucial for dark matter direct detection experiments, can therefore be calibrated with pulse shapes from gamma-sources., Comment: 11 pages (latex) including 6 postscript figures and 2 tables

The Heidelberg-Dark-Matter-Search (HDMS) experiment consists of two HPGe-detectors which operate in a unique configuration. The anticoincidence between the detectors will act as an effective background reduction method allowing to reach a sensitivity comparable to those of planned cryogenic experiments. The experiment is situated in the Gran Sasso Underground Laboratory and starts to take data now. New upper limits on WIMP-nucleon cross sections are obtained after 0.53 kg yr of measurement with one of the enriched 76Ge detectors of the Heidelberg–Moscow experiment. An energy threshold of 8.8 keV and a background level of 0.05 events/kg yr keV in the energy region between 8.8 and 100 keV was reached. The derived limits are at present the most stringent ones for spin independent interaction obtained by using only raw data without background subtraction.

Nuclear double beta decay provides an extraordinarily broad potential to search for beyond Standard Model physics, probing already now the TeV scale, on which new physics should manifest itself. These possibilities are reviewed here. First, the results of present generation experiments are presented. The most sensitive one of them — the Heidelberg–Moscow experiment in the Gran Sasso — probes the electron mass now in the sub eV region and will reach a limit of ~ 0.1 eV in a few years. Basing to a large extent on the theoretical work of the Heidelberg Double Beta Group in the last two years, results are obtained also for SUSY models (R-parity breaking, sneutrino mass), leptoquarks (leptoquark–Higgs coupling), compositeness, right-handed W boson mass and others. These results are comfortably competitive to corresponding results from high-energy accelerators like TEVATRON, HERA, etc. Second, future perspectives of ββ research are discussed. A new Heidelberg experimental proposal (GENIUS) is presented which would allow one to increase the sensitivity for Majorana neutrino masses from the present level of at best 0.1 eV down to 0.01 or even 0.001 eV. Its physical potential would be a breakthrough into the multi-TeV range for many beyond standard models. Its sensitivity for neutrino oscillation parameters would be higher than that for all present terrestrial neutrino oscillation experiments and of those planned for the future. It could probe directly the atmospheric neutrino problem and even the large angle solution of the solar neutrino problem. It would further, already in a first step, using only 100 kg of natural Ge detectors, cover almost the full MSSM parameter space for prediction of neutralinos as cold dark matter, making the experiment competitive to LHC in the search for supersymmetry.

We present a review of existing and planned dark matter direct detection experiments. The emphasis is on principle limitations for this detection technique and resulting consequences for future projects. We argue that the near future experiments, CDMS and HDMS, will give such stringent limits on WIMP–nucleon elastic cross sections that the next round of experiments will have to be either massive direction–sensitive detectors or massive ton–scale detectors with almost zero background. Candidate experiments with these requirements are shortly introduced like the newly announced GENIUS proposal. We also shortly discuss the implications of WIMP search results for accelerator experiments and vice versa.

It has recently been shown that in the framework of weak-scale softly broken supersymmetry the existence of a Majorana neutrino inevitably implies a finite (B-L)-violating ``Majorana'' mass ${m}_{M}$ for scalar neutrinos, with the effect of splitting the complex sneutrino field into two real fields separated in mass by $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{1}^{2}\ensuremath{-}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{2}^{2}=2|\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{m}{}_{M}^{2}|$. The existence of a finite Majorana sneutrino mass leads to new processes potentially observable at future colliders. Taking into account existing low-energy constraints, to find positive signals for electron sneutrinos will be very difficult, although not impossible. For muon and tau sneutrinos a dedicated search for Majorana masses has much better prospects.

Der Doppelbetazerfall bietet gegenwartig eine der vielversprechendsten Moglichkeiten, Physik jenseits des Standardmodells der Elementarteilchenphysik und jenseits der direkten Moglichkeiten gegenwartiger und zukunftiger Hochenergiebeschleuniger zu sondieren.

This communication describes the lessons we have to draw after the observation of neutrinoless ββ decay on a 6σ level by the enriched 76Ge experiment in Gran Sasso, for present and future experiments (a) to fulfill the task to confirm the present result (b) to deliver additional information on the main contributions of effective neutrino mass and right-handed weak currents etc. to the 0νββ amplitude. It is pointed out that presently running and planned experiments are not sensitive enough to check the present evidence on a reasonable time scale. More important, the only way to get information on the individual contributions of m, η, λ etc to the 0νββ amplitude is to go to completely different types of experiments, e.g. mixed-mode β+EC decay experiments, such as 124Xe decay, on a 1027 y sensitivity level.

The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated the large potential of double beta decay to search for new physics beyond the Standard Model. To increase by a major step the present sensitivity for double beta decay and dark matter search much bigger source strengths and much lower backgrounds are needed than used in experiments under operation at present or under construction. We present here a study of a project proposed recently, which would operate one ton of 'naked' enriched GErmanium-detectors in liquid NItrogen as shielding in an Underground Setup (GENIUS). It improves the sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe neutrino masses even down to 10^-3 eV. The first version would allow to test the atmospheric neutrino problem, the second at least part of the solar neutrino problem. Both versions would allow in addition significant contributions to testing several classes of GUT models. These are especially tests of R-parity breaking supersymmetry models, leptoquark masses and mechanism and right-handed W-boson masses comparable to LHC. The second issue of the experiment is the search for dark matter in the universe. The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment - with the same purity requirements but using only 100 kg of 76Ge or even of natural Ge - making the experiment competitive to LHC in the search for supersymmetry. The layout of the proposed experiment is discussed and the shielding and purity requirements are studied using GEANT Monte Carlo simulations. As a demonstration of the feasibility of the experiment first results of operating a 'naked' Ge detector in liquid nitrogen are presented., Comment: 22 pages, 12 figures, see also http://pluto.mpi-hd.mpg.de/~betalit/genius.html

The physics potential of GENIUS, a recently proposed double beta decay and dark matter experiment is discussed. The experiment will allow to probe neutrino masses down to 10−(2–3) eV. GENIUS will test the structure of the neutrino mass matrix, and therefore implicitly neutrino oscillation parameters comparable or superior in sensitivity to the best proposed dedicated terrestrial neutrino oscillation experiments. If the 10-3 eV level is reached, GENIUS will even allow to test the large angle MSW solution of the solar neutrino problem. Even in its first stage GENIUS will confirm or rule out degenerate or inverted neutrino mass scenarios, which have been widely discussed in the literature as a possible solution to current hints on finite neutrino masses and also test the νe ↔ νμ hypothesis of the atmospheric neutrino problem. GENIUS would contribute to the search for R-parity violating SUSY and right-handed W-bosons on a scale similar or superior to LHC. In addition, GENIUS would largely improve the current 0νββ decay searches for R-parity conserving SUSY and leptoquarks.