Ratios Of Nuclear Matrix Elements Research Articles

Favored neutrino mass mechanisms of the 0νββ-decay unified by an interpolating formula

The neutrino mass mechanisms of the neutrinoless double beta decay (0νββ-decay) generated within the left-right symmetric models are discussed by taking advantage of an interpolating formula for nuclear matrix element depending on the neutrino mass. Its application is justified by a weak dependence of mean square neutrino momentum, which is a properly scaled ratio of nuclear matrix elements for the light and heavy neutrino mass mechanisms, on decaying isotope. Due to this fact there is a single unified lepton number violating parameter including dependendence on all neutrino masses in the decay rate and the light and heavy neutrino mass mechanisms can be hardly distinguished by observing the 0νββ-decay on different isotopes. Further, a see-saw type neutrino mixing, which relates neutrino mixing in light and heavy neutrino sectors, is proposed. By considering the current limit on the 0νββ-decay half-life of 136Xe the regions of dominance of exchange of light and heavy neutrinos are identified.

Short-Range Correlations and the EMC Effect in Effective Field Theory.

We show that the empirical linear relation between the magnitude of the EMC effect in deep inelastic scattering on nuclei and the short-range correlation scaling factor a_{2} extracted from high-energy quasielastic scattering at x≥1 is a natural consequence of scale separation and derive the relationship using effective field theory. While the scaling factor a_{2} is a ratio of nuclear matrix elements that individually depend on the calculational scheme, we show that the ratio is independent of this choice. We perform Green's function MonteCarlo calculations with both chiral and Argonne-Urbana potentials to verify this and determine the scaling factors for light nuclei. The resulting values for ^{3}He and ^{4}He are in good agreement with experimental values. We also present results for ^{9}Be and ^{12}C extracted from variational MonteCarlo calculations.

New physics effects on neutrinoless double beta decay from right-handed current

We study the impact of new physics contributions to neutrinoless double beta decay arising from right-handed current in comparison with the standard mechanism. If the light neutrinos obtain their masses from Type-II seesaw within left-right symmetric model, where the Type-I contribution is suppressed to negligible extent, the right-handed PMNS matrix is the same as its left-handed counterpart, making it highly predictable and testable at next-generation experiments. It is very attractive, especially with recent cosmological constraint favoring the normal hierarchy under which the neutrinoless double beta decay is too small to be observed unless new physics appears as indicated by the recent diboson excess observed at ATLAS. The relative contributions from left- and right-handed currents can be reconstructed with the ratio between lifetimes of two different isotopes as well as the ratio of nuclear matrix elements. In this way, the theoretical uncertainties in the calculation of nuclear matrix elements can be essentially avoided. We also discuss the interplay of neutrinoless double beta decay measurements with cosmology, beta decay, and neutrino oscillation.

Sensitivity of muon capture to the ratios of nuclear matrix elements

It is shown that the observables in ordinary muon capture depend very sensitively on the ratios of nuclear matrix elements. This is demonstrated for the case of extracting ${g}_{P}{/g}_{A}$ from $\ensuremath{\gamma}\ensuremath{\nu}$-correlation experiments on ${}^{28}\mathrm{Si}$ and from the ratio of capture rates from hyperfine states in ${}^{11}\mathrm{B}$ and ${}^{23}\mathrm{Na}.$

Nuclear matrix elements from L/K electron capture ratios in 59Ni decay

Using a recent theoretical method, the ratio of nuclear matrix elements R = ( vF 0 220−√ 3 2 AF 0 221/ vF 0 211) was determined to be either 20.50 +0.35 −0.55 or 25.22 +0.28 −0.17 in the second-forbidden nonunique decay of 8 × 10 4 y 59Ni. These values of R were obtained from a value of L 3/K = 0.008 ± 0.002 found by subtracting the theoretical ratio (L 1 + L 2) K = 0.113 (based on Q PEC = 1070 ± 8 keV) from the total ratio L/K = 0.121 ± 0.002, which was measured with a reactor-produced, doubly-mass-separated 59Ni source introduced as gaseous nickel-ocene, (C 5H 5) 2, into a wall-less, anticoincidence, multiwire proportional counter. The 854–1008 eV L and the 8.33 keV K peaks were measured simultaneously.

The penetration effect in electric dipole internal conversion

Nuclear-structure-dependent contributions to the internal-conversion process are considered in conjunction with highly retarded electric dipole transitions. Formulas for a theory of anomalous internal conversion for electric transitions are given. These formulas are applied to explain the strong E1 anomalies for L conversion found experimentally by Asaro, Stephens, Hollander and Perlman. Two different types of anomalous matrix elements occur, one associated with the nuclear charge, the other with the nuclear current. It is found that the contribution associated with charge is negligible. In the current terms we distinguish two parts, the convection current and spin current, which are associated with different selection rules and generally both are important. From the empirical data of the L I and L II anomaly the sign of the ratio of nuclear matrix elements which gives the dominant contribution to the anomalous conversion amplitude is deduced. The anomalous nuclear matrix elements are evaluated for the single-particle model. Effects of pair correlation are discussed. The agreement with experiments is satisfactory.

Beta-decay of RaE; Evidence for the conserved vector current theory

Phenomenological limits for two independent ratios of nuclear matrix elements for Bi/sup 210/ were obtained and compared with experimental values of the energy-dependent shape correction factor and the electron polarization. Data are presented in graphical form. (L.N.N.)