Neutrinoless Double Beta Decay

In this Technical Design Report (TDR) we describe the NEXT-100 detector that will search for neutrinoless double beta decay (β β 0ν) in 136 Xe. The document formalizes the ANGEL design presented in our Conceptual Design Report (CDR). The baseline detector is designed to hold a maximum of about 150 kg of xenon at 15 bar, or 100 kg at 10 bar. This option builds in the capability to increase the total isotope mass by 50% while keeping the operating pressure at a manageable level. The ANGEL design calls for an asymmetric TPC, with photomultipliers behind a transparent cathode and position-sensitive light pixels behind the anode. We have chosen the low background R11410-10 PMTs for energy and timing and Hamamatsu MPPCs (S10362-11-050P model) as tracking pixels. Each individual PMT will be isolated from the gas by an individual, pressure resistant enclosure and will be coupled to the sensitive volume through a sapphire window coated with terphenyl-butadiene (TPB) . MPPCs will be arranged in Dice Boards (DB) holding 64 sensors each in an array of 8×8 sensors. The light tube will also be coated with TPB.

The last decade has witnessed both quantitative and qualitative progresses in Shell Model studies, which have resulted in remarkable gains in our understanding of the structure of the nucleus. Indeed, it is now possible to diagonalize matrices in determinantal spaces of dimensionality up to 10^9 using the Lanczos tridiagonal construction, whose formal and numerical aspects we will analyze. Besides, many new approximation methods have been developed in order to overcome the dimensionality limitations. Furthermore, new effective nucleon-nucleon interactions have been constructed that contain both two and three-body contributions. The former are derived from realistic potentials (i.e., consistent with two nucleon data). The latter incorporate the pure monopole terms necessary to correct the bad saturation and shell-formation properties of the realistic two-body forces. This combination appears to solve a number of hitherto puzzling problems. In the present review we will concentrate on those results which illustrate the global features of the approach: the universality of the effective interaction and the capacity of the Shell Model to describe simultaneously all the manifestations of the nuclear dynamics either of single particle or collective nature. We will also treat in some detail the problems associated with rotational motion, the origin of quenching of the Gamow Teller transitions, the double beta-decays, the effect of isospin non conserving nuclear forces, and the specificities of the very neutron rich nuclei. Many other calculations--that appear to have ``merely'' spectroscopic interest--are touched upon briefly, although we are fully aware that much of the credibility of the Shell Model rests on them.

The discovery of neutrino mass marks a turning point in elementary particle physics, with important implications for nuclear and astroparticle physics. Here I give a brief update, where I summarize the current status of three-neutrino oscillation parameters from current solar, atmospheric, reactor and accelerator neutrino data, discuss the case for sterile neutrinos and LSND, and also the importance of tritium and double beta decay experiments probing the absolute scale of neutrino mass. In this opininated look at the present of neutrino physics, I keep an eye in the future, and a perspective of the past, taking the oportunity to highlight Joe Schechter's pioneering contribution, which I have had the fortune to share, as his PhD student back in the early eighties.

The NEMO-3 experiment is located in the Modane Underground Laboratory (LSM) and has been taking data since 2003 with seven isotopes. It is searching for the double beta decay process with two (2νββ) or zero (0νββ) neutrinos emitted in the final state. Precision measurements of the half-life of the isotopes due to 2νββ decay have been performed and new results for T 2ν

The International Germanium Experiment (IGEX) has analyzed 117 mole yr of 76 Ge data from its isotopically enriched (86% 76 Ge) germanium detectors. Applying pulse-shape discrimination (PSD) to the more recent data, the lower bound on the half-life for neutrinoless double-beta decay of 76 Ge is: T yr (90% C.L.). This corresponds to an upper bound in the Majorana neutrino mass parameter, ( ) 25 2 / 1 10 57 . 1 0 × > ν ν m , between 0.33 eV and 1.35 eV, depending on the choice of theoretical nuclear matrix elements used in the analysis.

A detailed study of the muonic analogue of neutrinoless double beta decay, (µ − , µ +) conversion, has been carried out for the A=44 nuclear system. We studied several lepton number violating (LNV) mechanisms potentially triggering this process: exchange by light and heavy Majorana neutrinos as well as exchange by supersymmetric particles participating in R-parity violating interactions. The nuclear structure has been taken into account within the renormalized Quasiparticle Random Phase Approximation method. To our knowledge, this is the first realistic treatment of nuclear structure aspects of the (µ − , µ +) conversion. We estimated the rate of this process utilizing the existing experimental constraints on the parameters of the underlying LNV

The scintillation yields of CaF crystals with different doping concentration of Europium have been measured at low 2 temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first ''scintillating bolometer'' where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from a-particles in the energy region of interest for searches on double beta decay of 48 Ca can be achieved. q 1998 Elsevier Science B.V.

We review neutrino oscillation physics, including the determination of mass splittings and mixings from current solar, atmospheric, reactor and accelerator neutrino data. A brief discussion is given of cosmological and astrophysical implications. Non-oscillation phenomena such as neutrinoless double beta decay would, if discovered, probe the absolute scale of neutrino mass and also reveal their Majorana nature. Non-oscillation descriptions in terms of spin-flavor precession (SFP) and non-standard neutrino interactions (NSI) currently provide an excellent fit of the solar data. However they are at odds with the first results from the KamLAND experiment which imply that, despite their theoretical interest, non-standard mechanisms can only play a sub-leading role in the solar neutrino anomaly. Accepting the LMA-MSW solution, one can use the current solar neutrino data to place important restrictions on non-standard neutrino properties, such as neutrino magnetic moments. Both solar and atmospheric neutrino data can also be used to place constraints on neutrino instability as well as the more exotic possibility of $CPT$ and Lorentz Violation. Weillustrate the potential of future data from experiments such as KamLAND, Borexino and the upcoming neutrino factories in constraining non-standard neutrino properties.

The Colorado State University professor of physics studies the fundamental matter particles known as neutrinos, and an exceedingly rare instance of radioactive decay in which neutrinos-otherwise present in such decays-are nowhere to be found. [39] Determining features of the elusive particle known as a neutrino-through the observation of an extremely rare nuclear process called neutrinoless double-beta decay (The inclusion of short-range interactions in models of neutrinoless double-beta decay could impact the interpretation of experimental searches for the elusive decay. [34] The occasional decay of neutrons into dark matter particles could solve a long-standing discrepancy in neutron decay experiments. [33] The U.S. Department of Energy has approved funding and start of construction for the SuperCDMS SNOLAB experiment, which will begin operations in the early 2020s to hunt for hypothetical dark matter particles called weakly interacting massive particles, or WIMPs. [32] Thanks to low-noise superconducting quantum amplifiers invented at the University of California, Berkeley, physicists are now embarking on the most sensitive search yet for axions, one of today's top candidates for dark matter. [31]

This pedagogical overview will cover the current status of neutrino physics from an experimentalist's point of view, focusing primarily on oscillation studies. The evidence for neutrino oscillations will be presented, along with the prospects for further refinement of observations in each of the indicated regions of two-flavor oscillation parameter space. The next steps in oscillation physics will then be covered (under the assumption of three-flavor mixing): the quest for θ 13 , mass hierarchy and, eventually, leptonic CP violation. Prospects for non-oscillation aspects of neutrino physics, such as kinematic tests for absolute neutrino mass and double beta decay searches, will also be discussed briefly.

A new technique to enable the detection of a hypothetical process called neutrinoless double beta decay has been developed by an international team of physicists. [39] Determining features of the elusive particle known as a neutrino-through the observation of an extremely rare nuclear process called neutrinoless double-beta decay (The inclusion of short-range interactions in models of neutrinoless double-beta decay could impact the interpretation of experimental searches for the elusive decay. [34] The occasional decay of neutrons into dark matter particles could solve a long-standing discrepancy in neutron decay experiments. [33] The U.S. Department of Energy has approved funding and start of construction for the SuperCDMS SNOLAB experiment, which will begin operations in the early 2020s to hunt for hypothetical dark matter particles called weakly interacting massive particles, or WIMPs. [32] Thanks to low-noise superconducting quantum amplifiers invented at the University of California, Berkeley, physicists are now embarking on the most sensitive search yet for axions, one of today's top candidates for dark matter. [31]

We have used a newly presented self-consistent version of the BCSq RQRPA method for a nucleus-by-nucleus study of the double beta decay in the medium-heavy region. The results have been compared to the previously used approaches, namely the QRPA and the RQRPA approximations. We have shown that inclusion of the quasiparticle correlations at the BCS level reduces ground state correlations in the particle-particle channel of the proton-neutron interaction, resulting in the systematic reduction of the double beta decay matrix elements. q

We point out a novel possibility for neutrinos where all neutrino flavors can be part Dirac and part Majorana. Our primary motivation for this model comes from an attempt to use supersymmetric see-saw models to tie inflation, baryon asymmetry of the Universe and dark matter to the neutrino sector. The idea however could stand on its own, with or without supersymmetry. We present a realization of this possibility within an $S_3$ family symmetry for neutrino masses, where we obtain tri-bi-maximal mixing for neutrinos to the leading order. The model predicts that for the case of inverted hierarchy, the lower limit on the neutrino mass measured in neutrinoless double beta decay experiments is about a factor of two larger than the usual case.

I summarize the status of neutrino oscillations that follow from current data, including the status of the small parameters ratio of solar-over-atmospheric splitting and $\sin^2\theta_{13}$ characterizing the strength of CP violation in neutrino oscillations. I briefly discuss the impact of oscillation data on the prospects for probing the absolute scale of neutrino mass in neutrinoless double beta decay. I also comment on the theoretical origin of neutrino mass, mentioning recent attemps to explain current data from first principles.

EXO-200 is an experiment designed to search for double beta decay of 136Xe with a single-phase, liquid xenon detector. It uses an active mass of 110 kg of xenon enriched to 80.6% in the isotope 136 in an ultra-low background time projection chamber capable of simultaneous detection of ionization and scintillation. This paper describes the EXO-200 detector with particular attention

I discuss the theoretical background and the status of neutrino oscillation parameters from the current worlds' global data sample and latest flux calculations. I give their allowed ranges, best fit values and discuss the small parameters α ≡ ∆m 2 sol /∆m 2 atm and sin 2 θ13, which characterize CP violation in neutrino oscillations. I mention the significance of ββ0ν (neutrinoless double beta decay) and current expectations in view of oscillation results.

I summarize the present status of global analyses of neutrino oscillations, including the most recent KamLAND and K2K data, as well as the latest solar and atmospheric neutrino fluxes. I give the allowed ranges of the threeflavour oscillation parameters from the current worlds' global neutrino data sample, their best fit values and discuss the small parameters α ≡ ∆m 2 sol /∆m 2 atm and sin 2 θ13, which characterize the strength of CP violation in neutrino oscillations. I briefly discuss neutrinoless double beta decay and the LSND neutrino oscillation hint, as well as the robustness of the neutrino oscillation results in the presence of non-standard physics.

The operational characteristics of a Micromegas operating in pure xenon at the pressure range of 1 to 10 bar are investigated. The maximum charge gain achieved in each pressure is approximately constant, around 4 x 10 2 , for xenon pressures up to 5 bar and decreasing slowly above this pressure down to values somewhat above 10 2 at 10 bar.

We discuss constraints on a scenario of almost degenerate three-flavor neutrinos imposed by the solar and the atmospheric neutrino anomalies, hot dark matter, and neutrinoless double β decays. It is found that in the Majorana version of the model the region with relatively large θ 13 is favored and a constraint on the CP violating phases is obtained.

In this review we present the main features of the current status of neutrino physics. After a review of the theory of neutrino mixing and oscillations, we discuss the current status of solar and atmospheric neutrino oscillation experiments. We show that the current data can be nicely accommodated in the framework of three-neutrino mixing. We discuss also the problem of

The pseudo-spin symmetry is reviewed. A mapping that produces the separation of the total angular momentum into pseudoorbital and pseudo-spin degrees of freedom is discussed, together with the analytic transformations that take us from the normal parity space to the eigenstates of a pseudo-oscillator with one quanta less. The manyparticle version of the unitary transformation to the pseudo-SU(3) space is established. As an example, these symmetries are used to describe the double beta decay phenomenon in heavy deformed nuclei.

The discovery of neutrino mass establishes the need for physics beyond the Standard Model. I summarize the status of two- and three-neutrino oscillation parameters from current solar, atmospheric, reactor and accelerator data. Future neutrinoless double beta decay experiments will probe the nature of neutrinos, as well as the absolute scale of neutrino mass, also tested by tritium beta decay spectra and cosmological observations. Sterile neutrinos do not provide a good way to account for the LSND hint, which needs further confirmation. Finally I sketch the main theoretical ideas for generating neutrino mass.

Neutrinoless double beta decay data together with information on the absolute neutrino masses obtained from the future KATRIN experiment and/or astrophysical measurements give a chance to find CP violation in the lepton sector with Majorana neutrinos. We derive and discuss necessary conditions which make discovery of such CP violation possible for the future neutrino oscillation and mass measurements data. PACS numbers: 14.60.Pq, 26.65.+t, 95.85.Ry

... 2 , M. Nomachi 13 , RGH Robertson 4 , T. Shima 1 , M. Slunecka 7 , G. Shirkov 12 , A. Sissakian 12 , A ... detectors. MOON [7–9], Super-NEMO [16] and others [17] are spectroscopic experiments with ββ sources = detectors. Calorimetric ...

β-decay properties of neutron-rich Ca isotopes have been obtained. Half-life values were determined for the first time for 54 Ca (86 ± 7 ms), 55 Ca (22 ± 2 ms), and 56 Ca (11 ± 2 ms). The half-life of 230 ± 60 ms deduced for 53 Ca is significantly longer than reported previously, where the decay chain 53 K → 53 Ca → 53 Sc was considered. A delayed γ ray with energy 247 keV was identified following β decay of 54 Ca, and is proposed to depopulate the 1 + 1 level in 54 Sc. The β-decay properties compare favorably with the results of shell model calculations completed in the full pf-space with the GXPF1 interaction. The half-lives of the neutron-rich Ca isotopes are also compared with gross β-decay theory. The systematic trend of the neutron-rich Ca half-lives is consistent with the presence of a subshell gap at N = 32.

We apply the self-consistent renormalized protonneutron QRPA (RQRPA) method to calculate the two-neutrino double beta (2νββ) decay matrix elements associated with the ground-state and excited-state transitions of the 82 Se → 82 Kr decay. The RQRPA method is an extension of the pnQRPA method and promotes the Pauli exclusion principle violated by the pnQRPA ground state and yields more stable nuclear matrix elements with increasing strength of the proton-neutron interaction. In the present work the RQRPA wave functions are also used to evaluate 2νββ-decay rates to excited final states. The resulting theoretical half lives are compared with the new stringent experimental limits obtained by using a HPGe detector and external sources of enriched selenium.

A brief sketch is given of the present observational status and future prospects of the physics of neutrino mass, including a survey of the various theoretical schemes of neutrino mass generation. Emphasis is given to those which are motivated by present experimental hints from solar and atmospheric neutrinos, as well as from cosmological data related to the dark matter question. The conceptual importance of neutrino-less double beta decay as a distinctive signature of the Majorana character of neutrinos is stressed. Barring accidental cancellations this process gives the strongest laboratory constraint on neutrino mass.

We propose a novel detection concept for neutrinoless double-beta decay searches. This concept is based on a Time Projection Chamber (TPC) filled with high-pressure gaseous xenon, and with separated-function capabilities for calorimetry and tracking. Thanks to its excellent energy resolution, together with its powerful background rejection provided by the distinct double-beta decay topological signature, the design discussed in this Letter Of Intent promises to be competitive and possibly out-perform existing proposals for next-generation neutrinoless double-beta decay experiments. We discuss the detection principles, design specifications, physics potential and R&D plans to construct a detector with 100 kg fiducial mass in the double-beta decay emitting isotope Xe(136), to be installed in the Canfranc Underground Laboratory.

Using decays of a clean source of 12 N produced at the IGISOL facility, we have measured the breakup of the 12 C (12.71 MeV) state into three particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.

Theoretical results for two neutrinos in the nuclei 96Ru, 102Pd, 106Cd and 108Cd are presented. The study employs the Hartree-Fock-Bogoliubov model to obtain the wave functions of the parent and daughter nuclei, in conjunction with the summation method to estimate the double-beta decay nuclear matrix elements. The reliability of the intrinsic wave functions of 96, 102Ru, 96Mo, 102, 106, 108Pd and 106, 108Cd nuclei is tested by comparing the theoretically calculated spectroscopic properties with the available experimental data. The calculated half-lives T 1/2 2ν of 96Ru, 102Pd, 106Cd and 108Cd nuclei for 2ν β+β+, 2ν β+ EC and 2ν ECEC modes are presented. The effect of deformation on the nuclear transition matrix element M 2ν is also studied.

We consider tri-bimaximal lepton mixing within low-scale seesaw schemes where light neutrino masses arise from TeV scale physics, potentially accessible at the Large Hadron Collider (LHC). Two examples are considered, based on the A4 flavor symmetry realized within the inverse or the linear seesaw mechanisms. Both are highly predictive so that in both the light neutrino sector effectively depends only on three mass parameters and one Majorana phase, with no CP violation in neutrino oscillations. We find that the linear seesaw leads to a lower bound for neutrinoless double beta decay while the inverse seesaw does not. The models also lead to potentially sizeable decay rates for lepton flavor violating processes, tightly related by the assumed flavor symmetry.

In this review we present the main features of the current status of neutrino physics. After a review of the theory of neutrino mixing and oscillations, we discuss the current status of solar and atmospheric neutrino oscillation experiments. We show that the current data can be nicely accommodated in the framework of three-neutrino mixing. We discuss also the problem of the determination of the absolute neutrino mass scale through Tritium beta-decay experiments and astrophysical observations, and the exploration of the Majorana nature of massive neutrinos through neutrinoless double-beta decay experiments. Finally, future prospects are briefly discussed.

The angular correlation of the electrons emitted in the neutrinoless double beta decay (0ν2β) is presented using a general Lorentz invariant effective Lagrangian for the leptonic and hadronic charged weak currents. We show that the coefficient K in the angular correlation dΓ/d cos θ ∝ (1 − K cos θ) is essentially independent of the nuclear matrix element models and present its numerical values for the five nuclei of interest ( 76 Ge, 82 Se, 100 Mo, 130 Te, and 136 Xe), assuming that the 0ν2β-decays in these nuclei are induced solely by a light Majorana neutrino, νM . This coefficient varies between K = 0.81 (for the 76 Ge nucleus) and K = 0.88 (for the 82 Se and 100 Mo nuclei), calculated taking into account the effects from the nucleon recoil, the S and P -waves for the outgoing electrons and the electron mass. Deviation of K from its values derived here would indicate the presence of New Physics (NP) in addition to a light Majorana neutrino, and we work out the angular coefficients in several νM + NP scenarios for the 76 Ge nucleus. As an illustration of the correlations among the 0ν2β observables (half-life T 1/2 , the coefficient K, and the effective Majorana neutrino mass | m |) and the parameters of the underlying NP model, we analyze the left-right symmetric models, taking into account current phenomenological bounds on the right-handed WR-boson mass and the left-right mixing parameter ζ. 1

The NSF has chosen the site for the Deep Underground Science and Engineering Laboratory (DUSEL) to be in Lead, South Dakota. In fact, the state of South Dakota has already stepped up to the plate and contributed its own funding for the proposed lab, see http://www.sanfordlaboratoryathomestake.org/index.html. The final decision by NSF for funding the Initial Suite of Experiments for DUSEL will be made early in 2009. At that time the NSF Science Board must make a decision. Of order 200 experimentalists have already expressed an interest in performing experiments at DUSEL. In order to assess the interest of the theoretical community, the Center for Cosmology and Astro-Particle Physics (CCAPP) at The Ohio State University (OSU) organized a 3-day DUSEL Theory Workshop in Columbus, Ohio from April 4 - 6, 2008. The workshop focused on the scientific case for six proposed experiments for DUSEL: long baseline neutrino oscillations, proton decay, dark matter, astrophysical neutrinos, neutrino...

The discovery of neutrino mass establishes the need for physics beyond the Standard Model. I summarize the status of two-and three-neutrino oscillation parameters from current solar, atmospheric, reactor and accelerator data. Future neutrinoless double beta decay experiments will probe the nature of neutrinos, as well as the absolute scale of neutrino mass, also tested by tritium beta decay spectra and cosmological observations. Sterile neutrinos do not provide a good way to account for the LSND hint, which needs further confirmation. Finally I sketch the main theoretical ideas for generating neutrino mass.

I discuss the implications of the latest data on solar and atmospheric neutrinos which strongly indicate the need for physics beyond the Standard Model. I review the theoretical options for reconciling these data in terms of three-neutrino oscillations. Even though not implied by the data, bi-maximal models of neutrino mixing emerge as an attractive possibility. Supersymmetry with broken R-parity provides a predictive way to incorporate it, opening the possibility of testing neutrino anomalies at high-energy collider experiments such as the LHC or at the upcoming long-baseline or neutrino factory experiments. Reconciling, in addition, the hint provided by the LSND experiment requires a fourth, light sterile neutrino. The simplest theoretical scenarios are the most symmetric ones, in which two of the four neutrinos are maximally-mixed and lie at the LSND scale, while the others are at the solar mass scale. The lightness of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and the generation of ∆m 2 ⊙ & ∆m 2 atm all follow naturally from the assumed lepton-number symmetry and its breaking. These two basic schemes can be distinguished at neutral-current-sensitive solar & atmospheric neutrino experiments such as the Sudbury Neutrino Observatory. However, underground experiments have not yet proven neutrino masses, since there is a variety of alternative mechanisms. For example, flavour changing interactions can play an important rôle in the explanation of solar and of contained atmospheric data and could be tested through effects such as µ → e + γ, µ − e conversion in nuclei, unaccompanied by neutrino-less double beta decay. Conversely, the room is still open for heavy unstable neutrinos. A short-lived ν µ might play a rôle in the explanation of the atmospheric data. Finally, in the presence of a sterile neutrino ν s , a long-lived ν τ in the MeV range could delay the time at which the matter and radiation contributions to the energy density of the Universe become equal, reducing the density fluctuations on the smaller scales, and rescuing the standard cold dark matter scenario for structure formation. In this case the light ν e , ν µ and ν s would account for the solar & atmospheric data.

EXO-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of scintillation light in an ultra-lowbackground liquid xenon (LXe) detector. We describe initial measurements of dark noise, gain and response to xenon scintillation light of LAAPDs at temperatures from room temperature to 169 K-the temperature of liquid xenon. We also describe the individual characterization of more than 800 LAAPDs for selective installation in the EXO-200 detector.

NEXT is a new experiment to search for neutrinoless double beta decay using a 100 kg radio-pure high-pressure gaseous xenon TPC. The detector requires excellent energy resolution, which can be achieved in a Xe TPC with electroluminescence readout. Hamamatsu R8520-06SEL photomultipliers are good candidates for the scintillation readout. The performance of this photomultiplier, used as VUV photosensor in a gas proportional scintillation counter, was investigated. Initial results for the detection of primary and secondary scintillation produced as a result of the interaction of 5.9 keV X-rays in gaseous xenon, at room temperature and at pressures up to 3 bar, are presented. An energy resolution of 8.0% was obtained for secondary scintillation produced by 5.9 keV X-rays. No significant variation of the primary scintillation was observed for different pressures (1, 2 and 3 bar) and for electric fields up to 0.8 V cm-1 torr-1 in the drift region, demonstrating negligible recombination luminescence. A primary scintillation yield of 81 \pm 7 photons was obtained for 5.9 keV X-rays, corresponding to a mean energy of 72 \pm 6 eV to produce a primary scintillation photon in xenon.

We have reinvestigated the β decay of the three isomers of 116 Ag at the Holifield Radioactive Ion Beam Facility (HRIBF). Through the use of half-life information, we have been able to construct individual decay schemes for each isomer and correct what was a puzzling inconsistency with the published data, namely the β feeding of 2 + states by a 5 + isomer. Our results indicate that the feeding of these levels arises from a 3 + isomer in 116 Ag. A total of 271 γ -ray transitions (159 new) were assigned to 148 levels (94 new) from the β decay of 116 Ag m1,m2,gs . Significant deviations are observed from IBM-2 calculations for the decay of the 0 + and 2 + members of the previously assigned three-phonon quintuplet. Candidate states for the quadrupole-octupole quintuplet states and πg 9/2 -πp 1/2 , πg 9/2 -πp 3/2 , νh 11/2 -νs 1/2 , νh 11/2 -νd 3/2 , and νh 11/2 -νd 5/2 broken-pair states are assigned.

The decays of the very neutron rich Sn isotopes [135][136][137] Sn were studied at CERN/ISOLDE using isotopic and isobaric selectivity achieved by the use of a resonance ionization laser ion source and mass spectroscopy, respectively. Neutron decay rates, ␥-ray singles, and ␥-␥ coincidence data were collected as a function of time.

A new phase of a 116 Cd double β decay experiment is in progress in the Solotvina Underground Laboratory. Four enriched 116 CdWO 4 scintillators with total mass of 339 g are used in a set up, whose active shield is made of 15 natural CdWO 4 crystals (20.6 kg). The background rate in the energy interval 2.5-3.2 MeV is 0.03 counts/yr·kg·keV. The half-life for 2ν2β decay of 116 Cd is

The NEMO-2 tracking detector located in the Fréjus Underground Laboratory was designed as a prototype of the detector NEMO-3 to study 0ν and 2ν doublebeta decay (ββ) physics. After ten months of nearly continuous running with an enriched cadmium source (0.92 mol·y of 116 Cd) a ββ2ν half-life of T 1/2 = (3.75 ± 0.35(stat) ± 0.21(syst)) · 10 19 y was measured. Limits with 90% CL on the 116 Cd half-lives of 5.0 · 10 21 y for ββ0ν decay and of 1.2 · 10 21 y for ββ0νχ 0 decay with a Majoron (χ 0 ) were obtained. Theoretical predictions for 0ν and 2ν decays of 116 Cd are also presented.