New bound to the probability of 76Ge ββ decay to the 0 1 + 76Se level

Measurements were carried out at the underground low-background laboratory of the Baksan Neutrino Observatory using a detection system involving four ultrapure germanium detectors made from enriched ⁷⁶Ge. The sensitivity of the experiment to the detection of a ⁷⁶Ge double beta decay to the excited levels of the ⁷⁶Se nucleus was determined. As a result of 228-day measurements, the new bound to the time of ⁷⁶Ge half-decay to the ⁷⁶Se 0 ₁ ⁺ excited level is found to be T _1/2(2ν2β)≥6.2×10²¹ years (90% confidence level).     

Investigation of double-beta decay at the Institute of Theoretical and Experimental Physics (ITEP, Moscow)

Investigation of neutrinoless double-beta (2β0ν) decay is presently being considered as one of the most important problems in particle physics and cosmology Interest in the problem was quickened by the observation of neutrino oscillations. The results of oscillation experiments determine the mass differences between different neutrino flavors, and the observation of neutrinoless decay may fix the absolute scale and the hierarchy of the neutrino masses. Investigation of 2β0ν decay is the most efficient method for solving the problem of whether the neutrino is a Dirae or a Majorana particle, Physicists from the Institute of Theoretical and Experimental Physics (ITEP, Moscow) have been participating actively in solving this problem. They initiated and pioneered the application of semiconductor detectors manufactured from enriched germanium to searches for the double-beta decay of ⁷⁶Ge. Investigations with ⁷⁶Ge provided the most important results. At present, ITEP physicists are taking active part in four very large projects, GERDA. Majorana, EXO, and NEMO, which are capable of recording 2β0ν decay at a Majorana neutrino mass of 〈m _ν〉 ≈ 10^?2 eV.     

Majorons: A simultaneous solution to the large and small scale dark matter problems

It is shown that the existence of majorons, which enable a heavy neutrino, 500 eV ? m_νH ? 25 keV to decay into a light neutrino m_νL ? 8 eV and a majoron, with lifetime 10⁴ yr ? τ_νH ? 10⁸ yr can solve both the large and small scale dark matter problems. For a primordial “Zeldovich” spectrum of fluctuations the limits are $\text{m}{}_{\mathrm{<mtext>v</mtext><mtext>H</mtext>}}\text{?}\text{?}\text{550}\text{eV and}\text{τ}{}_{\mathrm{<mtext>v</mtext><mtext>H</mtext>}}$ > 10⁷ to 10⁸ yr (the ranges m_νH ? eV and τ_νH ? 10⁸ yr are allowed by the model but galaxy formation becomes problematic). The large scale dark matter problem is how to achieve the critical density as implied by inflation, the small scale problems deal with the halos of galaxies and galaxy formation and perturbation growth. The heavy neutrino could provide the solution to the small scale problem by initiating perturbation growth before decoupling. The decay products will be fast and thus not bound to the initial clumps, thus solving the large scale problem. The low mass relic neutrinos that were not decay products would remain bound in the gravitational potentials which grew from the initial perturbations. The resulting universe would be radiation dominated, which is consistent with present observations if H₀ ? 40 km/s/Mpc. An alternative solution can occur when m_νH ≈ 10 eV: the universe can again become matter dominated in the present epoch. This solution still allows H⁰ ～ 50 km/s/Mpc. The majoron model parameters which best fit the dark matter considerations are presented.     

Double-beta decay of 48Ca in the TGV experiment

The low-background, high-sensitivity Ge multidetector spectrometer TGV is used to study the double-beta decay of ⁴⁸Ca. Additional suppression of the recorded background is achieved with neutron shielding and a method for distinguishing β particles from γ rays by detector-pulse rise time. The estimates T _1/2 ^γγ2ν = (4.2 ± 2.4) × 10¹⁹ yr and T _1/2 ^γγ0ν > 1.5 × 10²¹ yr (at a 90% C.L.) for the double-beta decay of ⁴⁸Ca are obtained.     

New phase of the 116Cd 2β-decay experiment with 116CdWO4 scintillators

A new step of the ¹¹⁶Cd 2β-decay experiment is in progress at the Solotvina Underground Laboratory. The upgraded setup consists of four enriched ¹¹⁶CdWO₄ crystal scintillators of total mass 339 g. As an active shield, 15 CdWO₄ crystals (20.6 kg) are used. The background rate (in the energy interval 2.7–2.9 MeV) is 0.06 count/(yr kg keV), one order of magnitude lower than in the previous apparatus. Combined with results of preceding measurements, the half-life limit for the neutrinoless 2β decay of ¹¹⁶Cd to the ground state of ¹¹⁶Sn is determined as T _1/2(0ν)≥5.1×10²² yr with 90% C.L. The limits on T _1/2 for transitions to the excited 2 ₁ ⁺ and 0 ₁ ⁺ levels of ¹¹⁶Sn are 8.6×10²¹ and 4.1×10²¹ yr, respectively (at a 90% C.L.). For 0ν2β decay accompanied by the emission of one and two Majorons, the constraints on the half-life are T _1/2(0νM1)≥1.4×10²¹ yr and T _1/2 (0νM2)≥4.1×10²⁰ yr (at a 90% C.L.). The corresponding constraints on the neutrino mass and the neutrino-Majoron coupling constant are 〈m _v〉 ≤ 3.1 eV and 〈g _M〉 ≤ 1.9 × 10^?4, respectively.     

Germanium detector array — GERDA

GERDA will be a new experiment at the Laboratori Nazionali del Gran Sasso (LNGS) to study neutrinoless double beta decay of ⁷⁶Ge at background levels <10⁻³ cts/(keV kg y) at , two orders of magnitude lower than in the previous experiments. Bare Ge-diodes, enriched to 86% in ⁷⁶Ge, are operated in liquid argon complemented by a water shield to reduce the external backgrounds. Intrinsic backgrounds will be suppressed by the pulse shape analysis and segmented electrodes. In GERDAs first phase, the detector array will consist of the existing and refurbished detectors of the previous Heidelberg-Moscow and IGEX experiments. After one year of measurement, the setup should allow us to scrutinize the claimed observation of 0νββ decay in ⁷⁶Ge. In its second phase, GERDA will use an additional set of new enriched ⁷⁶Ge crystals, as segmented or point contact detectors. After 100 kg y the sensitivity will be ; this corresponds to an effective Majorana mass range from 0.1 eV to 0.2 eV.     

Neutrino masses,nuclear matrix elements,and the 0<Emphasis Type="Italic">νββ</Emphasis> decay of <Superscript>76</Superscript>Ge

Neutrino data, obtained from SNO, SK, CHOOZ, KamLAND, and WMAP, are used to establish the upper limit of 〈m_ν〉 relevant for the 0νββ. The decay of ⁷⁶Ge is discussed within different light-neutrino mass spectra and with different nuclear matrix elements.     

Neutron interactions with germanium isotopes and amorphous and crystalline GeO2

Coherent neutron scattering lengths and total cross sections have been measured on elemental and oxide samples of ordinary Ge and of isotopically enriched substances. From the experimental results the following values were obtained:

the coherent scattering lengths (in fm) of the bound atoms Ge(8.185±0.020);⁷⁰Ge(10.0±0.1);⁷²Ge(8.51±0.10);⁷³Ge(5.02±0.04);⁷⁴Ge(7.58±0.10) and⁷⁶Ge(8.2 ±1.5);

the absorption cross sections at 0.0253 eV (in barn) for Ge(2.20±0.04);⁷⁰Ge(2.9±0.2);⁷²Ge(0.8±0.2);⁷³Ge(14.4±0.4) and⁷⁴Ge(0.4±0.2);

the free cross sections for epithermal neutrons and the zero energy scattering cross sections.

On the basis of this data, the isotopic- and spin-incoherent cross sections and thes-wave resonance contributions to the coherent scattering lengths have been determined and discussed. Transmission measurements at 0.57 meV on amorphous and crystalline GeO₂ yielded for the amorphous sample an inelastic cross section eight times larger than for the crystalline samples. This effect corresponds to a clearly higher density of low energy states in the amorphous than in the crystalline substances.     

AMoRE: Collaboration for searches for the neutrinoless double-beta decay of the isotope of 100Mo with the aid of 40Ca100MoO4 as a cryogenic scintillation detector

The AMoRE (Advanced Mo based Rare process Experiment) Collaboration is planning to employ ⁴⁰Ca¹⁰⁰MoO₄ single crystals as a cryogenic Scintillation detector for studying the neutrinoless double-beta decay of the isotope ¹⁰⁰Mo. A simultaneous readout of phonon and scintillation signals is performed in order to suppress the intrinsic background. The planned sensitivity of the experiment that would employ 100 kg of ⁴⁰Ca¹⁰⁰MoO₄ over five years of data accumulation would be T _1/2 ^0ν = 3 × 10²⁶ yr, which corresponds to values of the effective Majorana neutrino mass in the range of 〈m _ν 〉 ～ 0.02–0.06 eV.     

A simple modification of the maximal mixing scenario for three light neutrinos

We suggest a simple modification of the maximal mixing scenario (withS ₃ permutation symmetry) for three light neutrinos. Our neutrino mass matrix has smaller permutation symmetryS ₂(ν _μ ?ν _e ), and is consistent with all neutrino experiments except the³⁷Cl experiment. The resulting mass eigenvalues for three neutrinos arem ₁≈(2.55?1.27)×10^?3eV,m _2,3≈(0.71?1.43)eV for Δm _LSND ² =0.5?2.0eV². Then these light neutrinos can account for ～(2.4?4.8)% (6.2?12.4%) of the dark matter forh=0.8 (0.5). Our model predicts theν _μ →ν _τ oscillation probability in the range sensitive to the future experiments such as CHORUS and NOMAD.     

Direct search for the neutrino mass in the beta decay of tritium: Status of the “Troitsk ν-mass” experiment

The results of the “Troitsk ν-mass” experiment on the search for the neutrino rest mass in tritium beta decay are presented. The investigation of the time dependence of the anomalous, bumplike structure at the end of the beta spectrum, reported earlier, gives an indication of the periodic shift of its position with respect to the endpoint with a period of 0.5 yr. An upper limit on the electron-antineutrino rest mass (m _ν<2.5eV/c ²) is derived after taking the bump into account.     

Excited states of154Nd studied through the decay of154Pr

Excited states in the neutron-rich doubly-odd nucleus⁷⁸As have been identified for the first time by proton-γ and γ-γ coincidence measurements via the⁷⁶Ge(α, pn) reaction at 32, 36, and 40 MeV beam energy. Four levels have been found to decay with lifetimes in the nanosecond region. The 5⁽⁺⁾ to (10⁺) states are ascribed to the (πg _9/2?νg _9/2) intruder two-quasiparticle configuration with some collective components in the 9⁽⁺⁾ and (10⁺) states.     

New limit on the half-life of 78Kr with respect to the 2K(2ν)-capture decay mode

The features of data accumulated for 1817 h in an experimental search for the 2K(2ν)-capture mode of ⁷⁸Kr decay are discussed. A new limit on the half-life for this decay is found: T _1/2≥2.3×10²⁰ yr (at a 90% C.L.).     

Optical and magneto-optical spectroscopy of thin ferromagnetic InMnAs layers

Spectral dependences of the refractive n(hν) and absorption k(hν) indices (hν= 1.2–4.4 eV) and the magneto-optical constant δ(hν) (hν = 0.5–4.4 eV) of the transverse Kerr effect of the InMnAs layers produced by laser deposition have been studied. The spectra of the diagonal ?(hν) and off-diagonal ?′hν) components of the permittivity tensor of the layers have been found. A comparison of the spectral dependences δ(hν), ?′(hν) and ?′₂ × (hν)² of the InMnAs and MnAs layers have been performed. Features in the spectra of the InMnAs layers have been attributed to a competition between the contributions of the In_{1 ? x} Mn _x As matrix and MnAs inclusions.     

Experimental consequences of νe−νμ mixing in neutrino beams

The experimental consequences of neutrino mixing and decay are analyzed. Existing neutrino beam experiments are consistent with a finite but small mixing angle unless |m_νμ²?m_νe²| ? (3.0 eV)². A finite ν_μ lifetime in the range τ/m_νμc² ? 7 × 10³ sec/MeV is shown to be consistent with experimental data.     

Scattering of slow neutrons by arsenic and selenium isotopes

Coherent neutron scattering lengths and free cross sections were measured for arsenic, for ordinary selenium and its isolated isotopes. By means of the Cristiansen filter technique the following scattering lengths for the bound atoms were obtained (in fm):b(As) =6.58(1) [b ₊=6.04(5) andb _?=7.47(8)],b(Se)=7.970(9),b(⁷⁶Se)=12.2(1),b(⁷⁷Se) =08.25(8),b(⁷⁸Se)=8.24(9),b(⁸⁰Se)=7.48(3) andb(⁸²Se)=6.34(8). Transmission measurements with neutrons of 1.26 eV and 5.19 eV resulted in an energy independent free scattering cross section for arsenic ofσ _{s, t}=5.40(3)b (in the eV-region). For ordinary selenium energy dependent free cross sections ofσ _{s, t}(1.26 eV)=7.9(1)b andσ _{s, t} (5.19 eV)=7.55(3)b were found. The results were compared with the resonance parameters of the nuclei and with different sets of potential scattering radii. Thus it could be concluded that there is no evidence for a bound state of the neutron-nucleus compound⁷⁵As+n but a clear evidence for strong bound levels of⁷⁶Se+n and⁷⁷Se+n.     

Optical and magneto-optical properties of room-temperature ferromagnetic In(Ga)MnAs layers, deposited by pulse laser ablation

Spectral dependences of refractive and absorption indices n(hν), k(hν) (hν=1.2-4.4 eV) and the transversal Kerr effect δ(hν) (hν=0.5-4.4 eV) in In(Ga)MnAs layers fabricated by laser deposition have been investigated. Spectra of the diagonal and off-diagonal components of the dielectric permittivity tensor of these layers have been calculated. Comparison of the spectral dependences δ(hν), ε′(hν) and ε′₂×(hν)² of the In(Ga)MnAs layers with similar spectra for MnAs has been carried out. Particular features in the spectra of the In(Ga)MnAs layers have been explained by a competition of contributions of the In_1−x(Ga_1−x)Mn_xAs host and MnAs inclusions.     

Search for double beta decay of 106Cd

A search for the β⁺β⁺, β⁺/EC, and EC/EC decays of ¹⁰⁶Cd was performed at the Modane Underground Laboratory (France) located at a depth of 4800 m w.e. using a TGV-2 multidetector germanium spectrometer. A preliminary evaluation is performed of the experimental data accumulated during the measurements (12 900 h) of ～13.6 g of ¹⁰⁶Cd (with an enrichment of 75%) and the spectrometer background without samples and with samples of natural Cd. New limits (at a 90% confidence level) of half-lives are obtained: T _1/2 ? 1.7 × 10²⁰ yr and T _1/2 ? 1.6 × 10²⁰ yr for the 0νEC/EC resonant decay of ¹⁰⁶Cd to the 2741 keV and 2718 keV excited states of the daughter nucleus ¹⁰⁶Pd and T _1/2 ? 4.2 × 10²⁰ yr for the 2νEC/EC decay to the ground state of ¹⁰⁶Pd (0⁺ → 0⁺, g.s.). The limits for other branches of the double beta decay of ¹⁰⁶Cd with transitions to the ground and excited states of ¹⁰⁶Pd are improved.     

High precision study of muon catalyzed fusion in D2 and HD gas

Muon catalyzed dd fusion in D₂ and HD gases in the temperature range from 28 to 350 K was investigated in a series of experiments based on a time-projection ionization chamber operating with pure hydrogen. All main observables in this reaction chain were measured with high absolute precision including the resonant and non-resonant ddμ formation rates, the rate for hyperfine transitions in dμ atoms, the branching ratio of the two charge symmetric fusion channels ³He + n and t + p and the muon sticking probability. The report presents the final analysis of the data together with a comprehensive comparison with calculations based on recent μCF theories. The energy of the loosely bound ddμ state with quantum numbers J = 1, ν = 1, which is central to the mechanism of resonant molecule formation, is extracted with precision ?₁₁(fit) = ?1.9651(7) eV. in impressive agreement with the latest theoretical results ?₁₁(theory) = ?1.9646 eV.     

Q values of the Ge and Mo double-beta decays

Penning trap measurements using mixed beams of ⁷⁶Ge–⁷⁶Se and ¹⁰⁰Mo–¹⁰⁰Ru have been utilized to determine the double-beta decay Q-values of ⁷⁶Ge and ¹⁰⁰Mo with uncertainties less than 200 eV. The value for ⁷⁶Ge, 2039.04(16) keV is in agreement with the published SMILETRAP value, 2039.006(50) keV. The new value for ¹⁰⁰Mo, 3034.40(17) keV is 30 times more precise than the previous literature value, sufficient for the ongoing neutrinoless double-beta decay searches in ¹⁰⁰Mo. Moreover, the precise Q-value is used to calculate the phase-space integrals and the experimental nuclear matrix element of double-beta decay.