Double beta decay

Double beta decay is a rare nuclear process changing the nuclear charge by two units leaving atomic number unchanged. The detection of the neutrino accompanied mode (A,Z)→(A,Z + 2) + 2e^? + &;2v^? ₂ with half-lives around 10²⁰ years is among the rarest decays ever observed. Of outmost importance for particle physics and especially neutrino physics, is the neutrinoless mode (A,Z)→(A,Z + 2) + 2e^?. This process is violating lepton number by two units and requires massive Majorana neutrinos, i.e. neutrino and antineutrino are identical. The current experimental status is reviewed and an outlook towards future activities is given.     

Double beta decay experiments

The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the 〈m _ν〉 at the level of (0.01–0.1) eV are considered.     

New limits on the double beta decay half-lives of 94Zr, 96Zr, 116Cd and 124Sn

Searches have been made for the double beta decays of ^{94, 96}Zr, ¹¹⁶Cd, and ¹²⁴Sn to excited states in their daughter nuclei. No evidence of any of these decays was found, and lower limits on the half-lives against such decays have been established to be 10¹⁸–10¹⁹ yr. In addition, the single beta decay half-life of ⁹⁶Zr has been established to be ⩾1.4×10¹⁸ yr.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

Double beta decay of 100Mo

Two-neutrino double beta decay of ¹⁰⁰Mo with half-life T _1/2=[7.2±0.9(stat)± 1.8(syst)]×10¹⁸ yr was detected using a liquid argon ionization chamber. With a C.L. of 68% (90%), the bounds on neutrinoless decay and decay with majoron emission were found to be 8.4(4.9)×10²¹ and 4.1(3.2)×10²⁰ yr, respectively. An analysis of all available results provides the average “world” value T _1/2=(8.0±0.7)×10¹⁸ yr for the two-neutrino decay of ¹⁰⁰Mo, and the corresponding nuclear matrix element is M _GT=0.118±0.005.     

Double beta decay and all that

This review illustrates the present state of knowledge and directions of interest in infrared spectroscopy through the discussion of a number of examples of recent work. After a brief introduction the survey falls into three parts. The first is concerned with problems of assignment and interpretation of the spectra of polyatomic molecules, and the calculation of force constants. The second deals with the study of some chemical systems by infrared methods, and in the final section mention is made of a number of specialized topics such as matrix-isolation techniques.     

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.     

Double beta decay andSU(4) symmetry

The amplitude for ββ decay with 2ν emission is shown to be related to (p,n) and (n,p) reactions on the initial and final states, respectively. The suppression of both ββ and (n,p) reaction is connected, and its origin is discussed by referring to theSU(4) symmetry. From present data on the first ones, we estimate the forward (n, p) strength of relevance for the ββ problem. The interest of the experimental determination of this strength is emphasized. Assuming a perturbative breaking of theSU(4) symmetry, results are given for⁷⁶Ge,⁸²Se,¹²⁸Te and¹³⁰Te.     

Double beta decay: A problem of particle, nuclear and atomic physics

A brief review of recent progress in the field of double beta decay is presented. Different aspects from particle, nuclear and atomic physics of both two-neutrino (2νββ) and neutrinoless (0νββ) modes of the double β decay are discussed. It is argued that the R-parity violating supersymmetry (SUSY) contributes to the 0νββ-decay predominantly via charged pion-exchange between decaying nucleons. Further, a problem of reliable determination of the 0νββ-decay nuclear matrix elements (NMEs) is addressed. It is manifested that the uncertainty associated with the calculation of the 0νββ-decay NMEs can be diminished by suitably chosen nuclear probes. A new possibility for the study of lepton number non-conservation is proposed, namely oscillations plus deexcitations of neutral atoms. A phenomenological analysis of this process leads to a resonant enhancement of the neutrinoless double electron capture, that has a Breit-Wigner form.     

Neutrinoless double beta decay

The physics potential of neutrinoless double beta decay is discussed. Furthermore, experimental considerations as well as the current status of experiments are presented. Finally, an outlook towards the future, work on nuclear matrix elements and alternative processes is given.     

Determination of the direction to a source of antineutrinos via inverse beta decay in Double Chooz

To determine the direction to a source of neutrinos (and antineutrinos) is an important problem for the physics of supernovae and of the Earth. The direction to a source of antineutrinos can be estimated through the reaction of inverse beta decay. We show that the reactor neutrino experiment Double Chooz has unique capabilities to study antineutrino signal from point-like sources. Contemporary experimental data on antineutrino directionality is given. A rigorous mathematical approach for neutrino direction studies has been developed. Exact expressions for the precision of the simple mean estimator of neutrinos’ direction for normal and exponential distributions for a finite sample and for the limiting case of many events have been obtained.     

Constraining neutrinoless double beta decay

A class of discrete flavor-symmetry-based models predicts constrained neutrino mass matrix schemes that lead to specific neutrino mass sum-rules (MSR). We show how these theories may constrain the absolute scale of neutrino mass, leading in most of the cases to a lower bound on the neutrinoless double beta decay effective amplitude.     

Neutrino-less double beta decay experiments

The observation of neutrinoless double beta decay would unambiguosly demonstrate that neutrinos are Majorana particles and would provide unique information about the ordering and absolute scale of neutrino masses. This very rare decay is actively searched for in a number of candidate isotopes. It violates lepton-number and is predicted by many extensions of the standard model. The most recent experimental results are reviewed. The technological advances and the most compelling requirements for the new generation of experiments are discussed.     

Bremsstrahlung spectrum in beta decay

The spectrum of the bremsstrahlung due to the complete slowing down in aluminium of beta particles belonging to the continuous spectrum, was calculated for an arrangement, in which the beta emitter is completely enclosed in an absorber. The Bethe-Heitler cross-section, corrected by an empirical factor, was used. A table is given which makes it possible to calculate bremsstrahlung spectra of beta emitters with their maximal energy between 0·6 MeV and 2·0 MeV; the necessary additional calculations are quite simple. The error in the calculation is practically determined by the uncertainty in the determination of the cross-section and is equal to about 10%.

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Gamow-Teller beta decay of 105Sn

The β-decay of ¹⁰⁵Sn was re-investigated at the ISOL facility of GSI Darmstadt by using a total absorption spectrometer. The experimental results include the half-life and β-delayed proton branching ratio of 32.7(5)s and 1.1(4) ^. 10^-4, respectively, and the contribution of electron capture to the ¹⁰⁵Sn decay of 0.420(35). The Gamow-Teller strength distribution peaking at 3.6MeV was measured, yielding a summed Gamow-Teller strength of 3.0(4). The latter data are discussed in comparison with shell-model predictions based on an empirical interaction.     

The beta decay of139I

With the⁹⁶Ru(⁵⁸Ni,2pn) reaction we produced¹⁵¹Yb₈₁ and studied its decay after online mass separation by γ-spectroscopic techniques. The decay populates the four positive parity single proton levels in the N=82 daughter nucleus¹⁵¹Tm and establishes I^π=1/2⁺ for the so far unknown¹⁵¹Tm low spin isomer. Using BCS theory proton single particle energies for¹⁵¹Tm were extracted from the observed excitation energies.