Relation between the 2νββ2\nu\beta\beta and 0νββ0\nu\beta\beta nuclear matrix elements

A formal relation between the GT part of the nuclear matrix elements M^0\nu}_{GT} of $0\nu\beta\beta$ decay and the closure matrix elements $M^{2\nu}_{cl}$ of $2\nu\beta\beta$ decay is established. This relation is based on the integral representation of these quantities in terms of their dependence on the distance $r$ between the two nucleons undergoing transformation. We also discuss the difficulties in determining the correct values of the closure $2\nu\beta\beta$ decay matrix elements.Comment: Talk at the MEDEX'11 workshop, Prague, June 201

Search for neutrinoless double beta decay with NEMO 3 experiment

NEMO 3 experiment is designed to search for neutrinoless double beta decay. It is located in the Modane Underground Laboratory (LSM) and has been taking data since February 2003. The half- lives of two neutrino beta decay have been measured for seven isotopes. No evidence of neutrinoless double beta decay has been found. The limits on both the half-lives of the neutrinoless double beta decay and the corresponding Majorana effective masses are derivedComment: 3 pages, 2 figures, 2 tables, PANIC08 Conference proceeding

Results from the NEMO 3 experiment

The aim of the NEMO 3 experiment is the search for neutrinoless double beta decay and precise measurement of two-neutrino double beta decay of several isotopes. The experiment has been taking data since 2003. Since no evidence for neutrinoless double beta decay of Mo100 and Se82 has been found, a 90% C.L. lower limit on the half-life of this process and corresponding upper limit on the effective Majorana neutrino mass are derived. The data are also interpreted in terms of alternative models, such as weak right-handed currents or Majoron emission. In addition, NEMO 3 has performed precision measurements of the two-neutrino double beta decay for seven different isotopes. The most recent experimental results of NEMO 3 are presented in this paper.Comment: 5 pages, 2 tables, talk at the 10th ICATPP Conference (Como, Italy, 8 - 12 October 2007

Relation between the 0νββ and 2νββ nuclear matrix elements reexamined

We show that the dominant Gamow-Teller part, M^(0ν)_(GT), of the nuclear matrix element governing the neutrinoless ββ decay is related to the matrix element M^(2ν)_(cl) governing the allowed two-neutrino ββ decay. That relation is revealed when these matrix elements are expressed as functions of the relative distance r between the pair of neutrons that are transformed into a pair of protons in the ββ decay. Analyzing this relation allows us to understand the contrasting behavior of these matrix elements when A and Z is changed; while M^(0ν)_(GT) changes slowly and smoothly, M^(2ν) has pronounced shell effects. We also discuss the possibility of phenomenological determination of the M^(2ν)_(cl) and from them of the M^(0ν)_(GT)values from the experimental study of the β^± strength functions

Neutrinoless double beta decay within Self-consistent Renormalized Quasiparticle Random Phase Approximation and inclusion of induced nucleon currents

The first, to our knowledge, calculation of neutrinoless double beta decay ($0\nu\beta\beta$-decay) matrix elements within the self-consistent renormalised Quasiparticle Random Phase Approximation (SRQRPA) is presented. The contribution from the momentum-dependent induced nucleon currents to $0\nu\beta\beta$-decay amplitude is taken into account. A detailed nuclear structure study includes the discussion of the sensitivity of the obtained SRQRPA results for $0\nu\beta\beta$-decay of $^{76}$Ge to the parameters of nuclear Hamiltonian, two-nucleon short-range correlations and the truncation of the model space. A comparision with the standard and renormalized QRPA is presented. We have found a considerable reduction of the SRQRPA nuclear matrix elements, resulting in less stringent limits for the effective neutrino mass.Comment: 13 pages, 3 figures, 1 tabl

Uncertainty in the 0νββ decay nuclear matrix elements

The nuclear matrix elements M0nu of the neutrinoless double-beta decay (0nubetabeta) are evaluated for 76Ge,100Mo,130Te, and 136Xe within the renormalized quasiparticle random phase approximation (RQRPA) and the simple QRPA. Three sets of single particle level schemes are used, ranging in size from 9 to 23 orbits. When the strength of the particle-particle interaction is adjusted so that the 2nubetabeta decay rate is correctly reproduced, the resulting M0nu values become essentially independent of the size of the basis, and of the form of different realistic nucleon-nucleon potentials. Thus, one of the main reasons for variability of the calculated M0nu within these methods is eliminated

Pion dominance in RPV SUSY induced neutrinoless double beta decay

At the quark level there are basically two types of contributions of R-parity violating SUSY (RPV SUSY) to neutrinoless double beta decay: the short-range contribution involving only heavy virtual superpartners and the long-range one with the virtual squark and neutrino. Hadronization of the effective operators, corresponding to these two types of contributions, may in general involve virtual pions in addition to the close on-mass-shell nucleons. It is known that the short-range contribution is dominated by the pion exchange. In the present paper we show that this is also true for the long-range RPV SUSY contribution and, therefore, the RPV SUSY contributes to the neutrinoless double beta decay dominantly via charged pion exchange between the decaying nucleons.Comment: 7 pages, 1 figure. Minor corrections, several comments and references adde

Erratum: Assessment of uncertainties in QRPA 0νββ0\nu\beta\beta-decay nuclear matrix elements [Nucl. Phys. A 766, 107 (2006)]

This is an erratum to our previously published paper.Comment: Accepted for publication in Nucl. Phys. A, see also nucl-th/050306

A deformed QRPA formalism for single and two-neutrino double beta decay

We use a deformed QRPA formalism to describe simultaneously the energy distributions of the single beta Gamow-Teller strength and the two-neutrino double beta decay matrix elements. Calculations are performed in a series of double beta decay partners with A = 48, 76, 82, 96, 100, 116, 128, 130, 136 and 150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock mean fields. The formalism includes a quasiparticle deformed basis and residual spin-isospin forces in the particle-hole and particle-particle channels. We discuss the sensitivity of the parent and daughter Gamow-Teller strength distributions in single beta decay, as well as the sensitivity of the double beta decay matrix elements to the deformed mean field and to the residual interactions. Nuclear deformation is found to be a mechanism of suppression of the two-neutrino double beta decay. The double beta decay matrix elements are found to have maximum values for about equal deformations of parent and daughter nuclei. They decrease rapidly when differences in deformations increase. We remark the importance of a proper simultaneous description of both double beta decay and single Gamow-Teller strength distributions. Finally, we conclude that for further progress in the field it would be useful to improve and complete the experimental information on the studied Gamow-Teller strengths and nuclear deformations.Comment: 33 pages, 19 figures. To be published in Phys. Rev.