Effects of quantum space time foam in the neutrino sector

We discuss violations of CPT and quantum mechanics due to interactions of neutrinos with space-time quantum foam. Neutrinoless double beta decay and oscillations of neutrinos from astrophysical sources (supernovae, active galactic nuclei) are analysed. It is found that the propagation distance is the crucial quantity entering any bounds on EHNS parameters. Thus, while the bounds from neutrinoless double beta decay are not significant, the data of the supernova 1987a imply a bound being several orders of magnitude more stringent than the ones known from the literature. Even more stringent limits may be obtained from the investigation of neutrino oscillations from active galactic nuclei sources, which have an impressive potential for the search of quantum foam interactions in the neutrino sector. Received: 5 June 2000 / Accepted: 12 July 2000     

The neutrinoless double-beta decay: A test for new physics

The neutrinoless double-beta decay is not allowed in the Standard Model (SM) but it is allowed in most Grand Unified Theories (GUTs). The neutrino must be a Majorana particle (identical with its antiparticle) and must have a mass to allow the neutrinoless double-beta decay. Apart of one claim that the neutrinoless double-beta decay in ⁷⁶Ge is measured, one has only upper limits for this transition probability. But even the upper limits allow to give upper limits for the electron Majorana neutrino mass and upper limits for parameters of GUTs and the minimal R-parity violating supersymmetric model. One further can give lower limits for the vector boson mediating mainly the right-handed weak interaction and the heavy mainly right-handed Majorana neutrino in left-right symmetric GUTs. For that, one has to assume that the specific mechanism is the leading one for the neutrinoless double-beta decay and one has to be able to calculate reliably the corresponding nuclear matrix elements. In the present contribution, one discusses the accuracy of the present status of calculating the nuclear matrix elements and the corresponding limits of GUTs and supersymmetric parameters.     

Two-neutrino double β decay of96Zr to excited 2+ state of96Mo

The two-neutrino double beta decay of⁹⁶Zr isotope for 0⁺ → 2⁺ transition has been studied in the PHFB model. In our earlier work, the reliability of the intrinsic wave functions of⁹⁶Zr and⁹⁶Mo isotopes has been established by obtaining an overall agreement between a number of theoretically calculated spectroscopic properties as well as half-lives of 2vββ decay for 0⁺ → 0⁺ transition and the available experimental data. In the present work, the half-life of 2vββ decay for 0⁺ ar 2⁺ transition T ₁ ^2/2v (0⁺ →²⁺) has been calculated using the same set of intrinsic wave functions.     

Beta decay of 101Sn

The β decay of the very neutron-deficient isotope ¹⁰¹Sn was studied at the GSI on-line mass separator using silicon detectors for recording charged particles and germanium detectors for γ-ray spectroscopy. Based on the β-delayed proton data the production cross-section of ¹⁰¹Sn in the ⁵⁰Cr + ⁵⁸Ni fusion-evaporation reaction was determined to be about 60nb. The half-life of ¹⁰¹Sn was measured to be 1.9(3)s. For the first time β-delayed γ-rays of ¹⁰¹Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065keV transitions in ¹⁰¹In. The results for the ¹⁰¹Sn decay as well as those from previous work on the ¹⁰³Sn decay are discussed by comparing them to predictions obtained from shell model calculations employing a new interaction in the ⁸⁸Sr to ¹³²Sn model space.     

Ion detection from beta decay and two-body decay experiments with laser-cooled atoms

Localized and cold samples of atoms produced with laser cooling and trapping techniques are a powerful tool for nuclear β-decay experiments. Recently we have concentrated on measurements of the momentum of the daughter ion produced, which leads to a variety of new observables. Angular distributions of the recoils with respect to the nuclear spin in β ⁺ decay are sensitive to non-standard model interactions. Measurements of the momentum of monoenergetic recoils from either electron capture or isomer γ decay would make it possible to search for particles with masses of 10s of keV.      

Phase shift analysis and extraction of structure functions for Coulomb distortion on (e, e'p) reactions at high electron energies

New results for the double beta decay of ⁷⁶ Ge are presented. They are extracted from data obtained with the HEIDELBERG-MOSCOW experiment, which operates five enriched ⁷⁶ Ge 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 T _1/2 ^2ν = [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 T _1/2 ^0ν > 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. Received: 22 August 2001 / Accepted: 18 October 2001     

Is the weak interaction constant really constant?

A comparison is made of the probability of the process of two neutrino double-beta decay for ⁸²Se and ⁹⁶Zr in direct (counter) and geochemical experiments. The experimental data for ¹³⁰Te are also analyzed. It is shown that the probability is systematically lower in geochemical experiments, which characterize the probability of decay a few billions years ago. In addition geochemical measurements on young minerals give lower values of T (¹³⁰Te) as compared to measurements on old minerals. It is proposed that this could be due to a change in the weak interaction constant with time. The possibilities of new precise measurements to be performed with the aid of counters and geochemical experiments are discussed. A new geochemical experiment with ¹⁰⁰Mo is proposed. Received: 24 February 2000 / Accepted: 4 March 2000     

Cerenkov emission as a positive tag of double beta decays in bolometric experiments

Active background reduction in high resolution calorimeters is a promising approach to achieve ultimate sensitivity in neutrinoless double beta decay experiments. We propose Cerenkov emission from beta rays in bolometric crystals as a viable alternative to scintillation. This novel approach could broaden the range of materials of interest for calorimetric searches of the double beta decay. We discuss the optical properties of TeO₂ crystals, as a show case.     

Control of bulk and surface radioactivity in bolometric searches for double-beta decay

The problem of background reduction in bolometers used to search for ββ(0ν) is reviewed with particular emphasis on bulk and surface radioactive contamination of the detectors.     

Neutron- and muon-induced background in underground physics experiments

Background induced by neutrons in deep underground laboratories is a critical issue for all experiments looking for rare events, such as dark matter interactions or neutrinoless ββ decay. Neutrons can be produced either by natural radioactivity, via spontaneous fission or (α, n) reactions, or by interactions initiated by high-energy cosmic rays. In all underground experiments, Monte Carlo simulations of neutron background play a crucial role for the evaluation of the total background rate and for the optimization of rejection strategies. The Monte Carlo methods that are commonly employed to evaluate neutron-induced background and to optimize the experimental setup, are reviewed and discussed. Focus is given to the issue of reliability of Monte Carlo background estimates. We dedicate this work to the memory of our friend and colleague Nicola Ferrari, who prematurely passed away in July 2006.     

Neutrino mass and unification

I discuss the implications of the observed masses and mixings of neutrinos for unification beyond the standard model and point out the important role that ongoing searches for the remaining mixing angle θ₁₃, neutrinoless double beta decay as well as possible searches for a Z^′ at LHC can play in this discussion.     

On the unusual properties of the 282 keV state in <Superscript>135</Superscript>Sb

Recently the first excited state in ¹³⁵Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d _5/2 proton coupled to the ¹³⁴Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d _5/2 and g _7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T _1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/2₁ ⁺→7/2₁ ⁺)≤3.0×10^-4 μ ² _N and B(E2;5/2₁ ⁺→7/2₁ ⁺)≤54e ² fm ⁴. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in ²¹¹Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.     

A simulation toolkit for electroluminescence assessment in rare event experiments

A good understanding of electroluminescence is a prerequisite when optimising double-phase noble gas detectors for Dark Matter searches and high-pressure xenon TPCs for neutrinoless double beta decay detection.A simulation toolkit for calculating the emission of light through electron impact on neon, argon, krypton and xenon has been developed using the Magboltz and Garfield programs. Calculated excitation and electroluminescence efficiencies, electroluminescence yield and associated statistical fluctuations are presented as a function of electric field. Good agreement with experiment and with Monte Carlo simulations has been obtained.     

New limits on the ββ decay of 130Te to excited states of 130Xe

Experimental limits on half-lives of the (0ν + 2ν)ββ decay of ¹³⁰Te to excited states of ¹³⁰Xe are obtained using low-background HPGe detectors. At the 90% CL, these limits are equal to 1.6 ^. 10²¹ y, 2.7 ^. 10²¹ y and 2.3 ^. 10²¹ y for transitions to the 2⁺ ₁, 2⁺ ₂ and 0⁺ ₁ levels, respectively. Received: 16 March 2001 / Accepted: 18 June 2001     

The investigation of the 2<Emphasis Type="Italic">νββ</Emphasis> decay by Pyatov method within quasiparticle random phase approximation formalism

The violated commutation condition between the total shell model Hamiltonian and Gamow-Teller operator (GT) has been restored by Pyatov method (PM). The considered nuclear model Hamiltonian in PM includes the separable GT residual interaction in ph and pp channels and is differentiated from the traditional schematic model by h ₀(restoration term). The influence of the h ₀ effective interaction on the 2νββ decay of ⁴⁸Ca, ⁷⁶Ge, ⁸²Se, ⁹⁶Zr, ¹⁰⁰Mo, ¹¹⁶Cd, ^128,130Te and ¹³⁶Xe is investigated. All the calculations have been done within the framework of standard QRPA. The results obtained by PM are compared with those of other approaches and experimental data. The influence of the restoration term on the stability of the 2νββ decay nuclear matrix elements is analysed.      

New BCS and renormalized QRPA formalism with application to double beta decay

A new analysis of the renormalized proton–neutron quasiparticle random phase approximation based on simultaneous recalculation of the one-body density matrix and the pairing tensor has been used to study the double beta decay. We demonstrated that inclusion of the quasiparticle correlations at the BCS level reduces ground state correlations in the particle–particle channel of the proton–neutron interaction. We also simplified the RQRPA equations significantly obtaining a low-dimensioned set of linear equations for the quasiparticle densities. The formalism was applied to the double beta decay of ⁷⁶Ge. Received: 4 January 1999 / Revised version: 29 March 1999     

Probing the mechanism of neutrinoless double beta decay with SuperNEMO

The SuperNEMO experiment is being designed to search for neutrinoless double beta decay. Its experimental technique of tracking and calorimetry provides the means to discriminate different underlying mechanisms for neutrinoless double beta decay by measuring the angular and energy distributions of electrons. The results of a study by the SuperNEMO Collaboration and F. Deppisch (in preparation) [7] for identifying light Majorana neutrino exchange and right-handed currents are presented.     

Neutrinoless Double Beta Decay: Status of Evidence

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.     

Decay of 1.643 h <Superscript>95</Superscript>Ru and its daughter's level structure

The decay of ⁹⁵Ru has been investigated by means of γ-ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo( α, n) ⁹⁵Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of ⁹⁵Tc is discussed in the framework of the projected shell model.     

Penning trap assisted decay spectroscopy of neutron-rich 115Ru

Exotic, neutron-rich ¹¹¹Mo and ¹¹⁵Ru nuclei, produced in proton-induced fission of ²³⁸U target, were separated with the IGISOL mass separator. The separator was coupled to the JYFLTRAP Penning trap to select the ions of a single, desired element out of the isobaric IGISOL beam. Monoisotopic samples of ¹¹⁵Ru and ¹¹¹Mo ions were observed with a microchannel plate detector after the trap or were implanted on a catcher foil for gamma- and beta-ray coincidence spectroscopy. In spite of short data taking time new gamma transitions were identified in the beta decay of very neutron-rich ¹¹⁵Ru.