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.     

THE RIGHT-HANDED CURRENTS OF NEUTRINOLESS DOUBLE β DECAY IN 48Ca

Right-handed Currents in 0νββ decay with lepton-number nonconservation is discussed by using two nucleons mechanism and the effective operator approach of nuclear matrix elements in this paper. The relation between the mixing parameter η of right-handed currents and the Majorana neutrino mass m_ν is calculated from the experimental decay lifetime of 0νββ decay in ⁴⁰Ca. Our results show that i) m_ν≤(18~23)eV, if |η|=0;ii) |η|≤(1.6~2)×10^－5, if m_ν=0     

The Decay of 120Ba

¹²⁰Ba was produced by 68MeV ¹⁶O beam bombarding a 2mg/cm² thick ¹⁰⁶Cd target and fluorated in a halium-jet ion source.The decay of on-line mass separated activity ¹²⁰Ba has been studied by γ-X,γ-γ γ-β coincidence measurements.Its halflife was measured to be 24±2s.The total decay energy was extracted to be Q_EC=5.0±0.3MeV.A simple decay scheme has been proposed.     

A highly efficient HPGE gamma-ray spectrometer for investigating ββ decay to excited states

A new low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm³ is developed to investigate rare nuclear processes such as resonance neutrinoless double electron capture and two-neutrino double beta decay to excited states of daughter nuclei. The spectrometer is installed at the Modane underground laboratory (France) at a depth of 4800 m w.e. The spectrometer background is measured and the spectrometer sensitivity is determined for measuring sources of double beta decay.     

A large Hilbert space QRPA and RQRPA calculation of neutrinoless double beta decay

A large Hilbert space is used for the calculation of the nuclear matrix elements governing the light neutrino mass mediated mode of neutrinoless double beta decay (Ovββ-decay) of⁷⁶ Ge,¹⁰⁰ Mo,¹¹⁶ Cd,¹²⁸ Te, and¹³⁶ Xe within the proton-neutron quasiparticle random phase approximation (pn-QRPA) and the renormalized QRPA with proton-neutron pairing (full-RQRPA) methods. We have found that the nuclear matrix elements obtained with the standard pn-QRPA for several nuclear transitions are extremely sensitive to the renormalization of the particle-particle component of the residual interaction of the nuclear hamiltonian. Therefore the standard pn-QRPA does not guarantee the necessary accuracy to allow us to extract a reliable limit on the effective neutrino mass. This behavior already known from the calculation of the two-neutrino double beta decay matrix elements, manifests itself in the neutrinoless double-beta decay but only if a large model space is used. The full-RQRPA, which takes into account proton-neutron pairing and considers the Pauli principle in an approximate way, offers a stable solution in the physically acceptable region of the particle-particle strength. In this way more accurate values on the effective neutrino mass have been deduced from the experimental lower limits of the half-lifes of neutrinoless double beta decay.     

Nuclear moments for the neutrinoless double beta decay

A derivation of the neutrinoless double beta decay rate, specially adapted for nuclear structure calculations, is presented. It is shown that the Fourier-Bessel expansion of the hadronic currents, jointly with angular momentum recoupling, leads to very simple final expressions for the nuclear form factors. This greatly facilitates the theoretical estimate of the half-life. Our approach does not require the closure approximation, which, however, can be implemented if desired. The method is exemplified for ββ decay ⁴⁸Ca → ⁴⁸Ti, both within the QRPA and a shell-model like model.     

New limits on double beta decay of 76Ge

New results are presented from an experiment on double beta decay of ⁷⁶Ge carried out with two Ge Li detectors in the Mont Blanc tunnel. No evidence has been found for neutrinoless double beta decay, and the obtained lower limit of the half lifetime (1.2 × 10²³ yr) is discussed in terms of the mass of Majorana neutrinos and of the possible presence of right-handed currents.     

Pinning down the mechanism of neutrinoless double beta decay with measurements in different nuclei

A measurement of neutrinoless double beta decay in one isotope does not allow us to determine the underlying physics mechanism. We discuss the discrimination of mechanisms for neutrinoless double beta decay by comparing ratios of half-life measurements for different isotopes. Six prominent examples for specific new physics contributions to neutrinoless double beta decay are analyzed. We find that the change in corresponding ratios of half lives varies from 60% for supersymmetric models up to a factor of 5-20 for extra-dimensional and left-right-symmetric mechanisms.     

Absolute Measurement of Important Branching Fractions of the Ds Meson

Absolute measurement of branching fractions of purely leptonic decay, semi-leptonic decay and φπ⁺ decay of the D_s meson at a c.m. energy of 4.03 GeV were completed from the BES experiment at the BEPC electron-positron collider. The method by using combined confidence level for pion and kaon separation, the D_s single and double tagging technology, and the maximum likelihood functions in the estimate of the D_s branching fractions are described in details. Discussion and comments on these physics results are made. Prospect for improved measurement of D_s physics in future is also given.     

First Experimental Determination of Half-Life for New Nuclide 65Se

By using experimental data obtained from the measurement of beta-delayed proton decay of ⁶⁵Se produced in ⁴⁰Ca(²⁸Si,3n)reaction,the absolute detection efficiency of particle telescope for rotating radioactive source was imitatively calcu-lated.The half-life of ⁶⁵Se was thus accurately determined to be 9.6_-4.1^+5.3 ms.The β-delayed proton energy of ⁶⁵Se was 3.70±0.08MeV.The partial decay scheme of ⁶⁵Se β-delayed proton decay was revised and proposed.     

Calculation of double beta decay rates and the neutrino mass

Predictions for 2v and 0v double beta decay rates are given for all nuclei with A ⩾ 70, for which double beta decay is energetically allowed. These predictions are based on detailed nuclear structure studies of the beta strength distribution and replace earlier estimates basing mostly on phase space considerations. New and more stringent limits on the Majorana neutrino mass are deduced from existing double beta decay experiments. Since the collective effects arising from spin-isospin as well as quadrupole-quadrupole forces are found to lead to a strong reduction of the nuclear matrix elements for two-neutrino double beta decay, but to have only minor influence on the matrix elements M^0v for the neutrinoless decay mode, the smaller limits for m_v result mainly from the fact that the widely used scaling procedure underestimates the 0_v matrix elements. It is further discussed to what extent interference between different neutrinos affects the obtained mass limits.     

Neutrinoless Double Beta Decay-A New Formalism

A new method-the operator expansion method is used in neutrinoless double beta decay processes. Both the neutrino mass and mixing of right-handed leptonic current are included. It is shown that for nuclear neutrinoless double beta decay in 2n mechanism, there appear some new terms besides the terms given by the conventional treatment based on closure approximation. The ββ with a Majoron emission is also discussed.     

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.     

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.     

Decays of Dsj*(2317) and Dsj(2460) Mesons in the Quark Model

We study the decay widths of the narrow resonances D_sj^*(2317) and D_sj(2460) in the chiral quark model, together with the well-known D^* and D_s^* mesons. All the parameters in our calculation are taken from Godfrey and Isgur's quark model except the π⁰－η mixing angle which is fixed by the D_s^* decay widths. The calculated electromagnetic decay widths agree with those from other groups and the experimental data available quite well. However, the pionic decay widths of D_sj(2317) and D_sj(2460) are too small to fit the experimental data. We suspect that the simple chiral quark pion axial-vector interaction Hamiltonian is not suitable for hadron strong decays of D_sj(2317) and D_sj(2460).     

Neutrinoless double beta decay and a new limit on the lepton number violation

We have calculated the neutrinoless double beta decay rate of ⁷⁶Ge. We take into account for the first time a relativistic correction to the nuclear current including weak magnetism. Its effect is to cancel a considerable part of the decay amplitude and we obtain less stringent upper limits on the neutrino Majorana mass and the right-handed weak leptonic current compared with previous calculations.     

Radial excitation states of η and η' in the chiral quark model

A chiral quark model is applied to calculate the spectra of pseudoscalar mesons η and η'. By analyzing the obtained spectra, we find that the mesons η'(2¹S₀), η(4¹S₀), η'(3¹S₀) and η'(4¹S₀) are the possible candidates of η(1760), X(1835), X(2120) and X(2370). The strong decay widths of these pseudoscalars to all the possible two-body decay channels are calculated within the framework of the ³P₀ model. Although the total width of η'(2¹S₀) is compatible with the BES Collaboration's experimental value for η(1760), the partial decay width to ωω is too small, which is not consistent with the BES result. If X(1835) is interpreted as η(4¹S₀), the total decay width is compatible with the experimental data, and the main decay modes will be mπ a₀(980) and m π a₀(1450), which needs to be checked experimentally. The assignment of X(2120) and X(2370) to η'(3¹S₀) and η'(4¹S₀) is disfavored in the present calculation because of the incompatibility of the decay widths.     

On neutrinoless double beta decay in the minimal left–right symmetric model

We analyze the general phenomenology of neutrinoless double beta decay in the minimal left–right symmetric model. We study under which conditions a New Physics dominated neutrinoless double beta decay signal can be expected in the future experiments. We show that the correlation among the different contributions to the process, which arises from the neutrino mass generation mechanism, can play a crucial role. We have found that, if no fine tuned cancelation is involved in the light–active neutrino contribution, a New Physics signal can be expected mainly from the $W_R$ – $W_R$ channel. An interesting exception is the $W_L$ – $W_R$ channel which can give a dominant contribution to the process if the right-handed neutrino spectrum is hierarchical with $M_1\lesssim $  MeV and $M_2,M_3\gtrsim $  GeV. We also discuss if a New Physics signal in neutrinoless double beta decay experiments is compatible with the existence of a successful Dark Matter candidate in the left–right symmetric models. It turns out that, although it is not a generic feature of the theory, it is still possible to accommodate such a signal with a KeV sterile neutrino as dark matter.     

Branching ratio of rare decay B0(Bs)→γνν

The three-body decay B⁰(B_s)→γνν can occur via penguin and box diagrams in the Standard Model (SM). These channels are useful to determine the decay constant f_B (f_Bs) and B (B_s) meson wave function. Using the B meson wave function determined in hadronic B (B_s) decays, we calculate and get the branching ratio of order 10^－9 and 10^－8 for B⁰ and B_s decay, respectively. They agree with previous calculations.     

Measurements of events simulating 2β-decay using a nuclear photoemulsion with molybdenum filling

The possibility of neutrinoless double beta decay is studied in the photoemulsion experiment with Mo-100 isotope. The results of measurements of positron-nucleus collisions for the purpose of estimating the background events simulating 2β-decay in the nuclear photoemulsion region adjoining molybdenum conglomerates are presented.