The gallium anomaly revisited Kostensalo, J.; Suhonen, J.; Giunti, C. ...
Physics letters. B,
08/2019, Letnik:
795
Journal Article
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The gallium anomaly, i.e. the missing electron-neutrino flux from 37Ar and 51Cr electron-capture decays as measured by the GALLEX and SAGE solar-neutrino detectors, has been among us already for ...about two decades. We present here a new estimate of the significance of this anomaly based on cross-section calculations using nuclear shell-model wave functions obtained by exploiting recently developed two-nucleon interactions. The gallium anomaly of the GALLEX and SAGE experiments is found to be smaller than that obtained in previous evaluations, decreasing the significance from 3.0σ to 2.3σ. This result is compatible with the recent indication in favor of short-baseline ν¯e disappearance due to small active-sterile neutrino mixing obtained from the combined analysis of the data of the NEOS and DANSS reactor experiments.
The electron spectral shapes corresponding to the low-Qβ−-decay transitions Sm151(5/2g.s.−)→Eu151(5/2g.s.+), Sm151(5/2g.s.−)→Eu151(7/21+), Tm171(1/2g.s.+)→Yb171(1/2g.s.−), ...Tm171(1/2g.s.+)→Yb171(3/21−), Pb210(0g.s.+)→Bi210(1g.s.−), and Pb210(0g.s.+)→Bi210(01−) have been computed using beta-decay theory with several refinements for these first-forbidden nonunique (ff-nu) β− transitions. These ff-nu β− transitions have non-trivial electron spectral shapes with transition nuclear matrix elements (NMEs) computed by using the microscopic Interacting Boson-Fermion Model (IBFM-2) for the decays of 151Sm and 171Tm, and the nuclear shell model (NSM) for the decay of 210Pb. Within the respective Q windows, the computed ff-nu electron spectral shapes deviate maximally at sub-percent level from the universal allowed shape, except for the transition Pb210(0g.s.+)→Bi210(1g.s.−), where the maximal deviation is some 2.7%. This confirms that the so-called ξ approximation is fairly good for most of these low-Qβ− transitions and thus the allowed shape is a rather good first approximation. Our computed spectral shapes could be of interest for experiments aiming to measure the cosmic neutrino background (CνB), like the PTOLEMY experiment. We have also derived CνB cross sections for the ground-state transitions of the considered nuclei at the β endpoint. Our findings indicate that more work on the atomic mismatch correction is needed in the future in order to extract reliable and precise CνB cross sections for any nuclear target.
Large-scale shell-model calculations were carried out for the half-lives and branching ratios of the 2νββ decay of 76Ge to the ground state and the lowest three excited states 21+, 02+ and 22+ in ...76Se. In total, the wave functions of more than 10,000 intermediate 1+ states in 76As were calculated in a three-step procedure allowing an efficient use of the available computer resources. In the first step, 250 lowest states, below some 5 MeV of excitation energy, were calculated without truncations within a full major shell 0f5/2−1p−0g9/2 for both protons and neutrons. The wave functions of the rest of the states, up to some 30 MeV, were computed in two more steps by introducing two consecutive stages of truncation. The computed magnitudes of the 2νββ nuclear matrix elements (including the value of the axial-vector coupling gA), |M2ν|gA2, converged to the values 0.168gA2, 1.2×10−3gA2, 0.121gA2, and 3.1×10−3gA2 for the 0g.s.+, 21+, 02+, and 22+ states, respectively. Using up-to-date phase-space integrals, the corresponding branching ratios were derived to be 99.926%, 4.4×10−5%, 0.074% and 2.5×10−7%. The experimental half-life (1.926±0.094)×1021 yr of the ground-state transition was used to derive the value gA=0.80±0.01 for the axial-vector coupling, which is consistent with other shell-model calculations suggesting a quenched value of gA. Using this value of gA, predictions for the transition half-lives were derived.
We perform the first consistent calculation of elastic-scattering and inelastic-scattering structure functions for spin-dependent WIMP-nucleus scattering off 183W in a microscopic nuclear-theory ...framework. The nuclear structure calculations are performed in the microscopic interacting boson-fermion model (IBFM-2). Our results show that while 183W is very insensitive to spin-dependent elastic scattering, the structure function for inelastic scattering is quite sizable at small momentum transfers. Moreover, to our knowledge 183W provides the first studied case where inelastic scattering can compete with elastic scattering as the primary detection signal.
Neutrinoless double-electron capture Blaum, K.; Eliseev, S.; Danevich, F. A. ...
Reviews of modern physics,
12/2020, Letnik:
92, Številka:
4
Journal Article
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Double-beta processes play a key role in the exploration of neutrino and weak interaction properties, and in the searches for effects beyond the standard model. During the last half century many ...attempts were undertaken to search for double-beta decay with emission of two electrons, especially for its neutrinoless mode 0 ν 2 β − , the latter having still not been observed. Double-electron capture (2EC) was not yet in focus because of its in general lower transition probability. However, the rate of neutrinoless double-electron capture 0 ν 2 EC can experience a resonance enhancement by many orders of magnitude when the initial and final states are energetically degenerate. In the resonant case, the sensitivity of the 0 ν 2 EC process can approach the sensitivity of the 0 ν 2 β − decay in the search for the Majorana mass of neutrinos, right-handed currents, and other new physics. An overview of the main experimental and theoretical results obtained during the last decade in this field is presented. The experimental part outlines search results of 2EC processes and measurements of the decay energies for possible resonant 0 ν 2 EC transitions. An unprecedented precision in the determination of decay energies with Penning traps has allowed one to refine the values of the degeneracy parameter for all previously known near-resonant decays and has reduced the rather large uncertainties in the estimate of the 0 ν 2 EC half-lives. The theoretical part contains an updated analysis of the electron shell effects and an overview of the nuclear-structure models, in which the nuclear matrix elements of the 0 ν 2 EC decays are calculated. One can conclude that the decay probability of 0 ν 2 EC can experience a significant enhancement in several nuclides.
In this work we report on the effects of short-range correlations upon the matrix elements of neutrinoless double beta decay (0νββ). We focus on the calculation of the matrix elements of the ...neutrino-mass mode of 0νββ decays of 48Ca and 76Ge. The nuclear-structure components of the calculation, that is the participant nuclear wave functions, have been calculated in the shell-model scheme for 48Ca and in the proton–neutron quasiparticle random-phase approximation (pnQRPA) scheme for 76Ge. We compare the traditional approach of using the Jastrow correlation function with the more complete scheme of the unitary correlation operator method (UCOM). Our results indicate that the Jastrow method vastly exaggerates the effects of short-range correlations on the 0νββ nuclear matrix elements.
Urbanization acts as a filter on bird species behavioral traits so that only few species can tolerate urban constraints. We analyzed how behavioral traits (nesting, feeding, and migratory habits) of ...breeding bird species affect their frequency of occurrence in the urban centers of 38 European towns. We used binary logistic regression analysis to predict the bird species traits belonging to each trait group. A total of 108 species (21% of the European breeding bird species) were found to breed in the European town centers. According to our broad-scale analyses the bird species most frequently breeding in town centers nest in buildings and/or buildings have diverse diets, in trees (40%) and are resident omnivores, or relied on seeds or fruits as their sources of food. However, almost all bird species also fed on arthropods (92%) during the breeding season. Only a few urban bird species bred on the ground. Four out of the studied 108 species were non-native and five species were predators. Our broad-scale results from Europe indicate that bird species with different behavioral traits can respond differently to urbanization. Bird species that nest in cavities/buildings have diverse diets, that benefit a resident way-of-life, may have an advantage in living and settling in European town centers. Our results from Europe may provide insights related to the development of bird assemblages in the urban core areas of the New World.
In this work we use the recently measured neutron occupancies in the 76Ge and 76Se nuclei as a guideline to define the neutron quasiparticle states in the 1p0f0g shell. We define the proton ...quasiparticles by inspecting the odd-mass nuclei adjacent to 76Ge and 76Se. We insert the resulting quasiparticles in a proton–neutron quasiparticle random-phase approximation (pnQRPA) calculation of the nuclear matrix element of the neutrinoless double beta (0νββ) decay of 76Ge. A realistic model space and effective microscopic two-nucleon interactions are used. We include the nucleon–nucleon short-range correlations and other relevant corrections at the nucleon level. It is found that the resulting 0νββ matrix element is smaller than in the previous pnQRPA calculations, and closer to the recently reported shell-model results.
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