Angular Distributions of Emitted Electrons in the Two-Neutrino ββ Decay

The two-neutrino double-beta decay (2νββ-decay) process is attracting more and more attention of the physics community due to its potential to explain nuclear structure aspects of involved atomic nuclei and to constrain new (beyond the Standard model) physics scenarios. Topics of interest are energy and angular distributions of the emitted electrons, which might allow the deduction of valuable information about fundamental properties and interactions of neutrinos once a new generation of the double-beta decay experiments will be realized. These tasks require an improved theoretical description of the 2νββ-decay differential decay rates, which is presented. The dependence of the denominators in nuclear matrix elements on lepton energies is taken into account via the Taylor expansion. Both the Fermi and Gamow-Teller matrix elements are considered. For nuclei of experimental interest, relevant phase-space factors are calculated by using exact Dirac wave functions with finite nuclear size and electron screening. The uncertainty of the angular correlation factor on nuclear structure parameters is discussed. It is emphasized that the effective axial-vector coupling constant gAeff can be determined more reliably by accurately measuring the angular correlation factor.

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Two neutrino double-beta decay and effective axial-vector coupling constant

EPJ Web of Conferences ◽

10.1051/epjconf/201819402002 ◽

2018 ◽

Vol 194 ◽

pp. 02002

Author(s):

Fedor Šimkovic ◽

Rastislav Dvornický ◽

Dušan Štefánik

Keyword(s):

Beta Decay ◽

Axial Vector ◽

Double Beta Decay ◽

Matrix Elements ◽

Coupling Constant ◽

Vector Coupling ◽

Majorana Particle ◽

Vector Coupling Constant ◽

Novel Approach ◽

Axial Vector Coupling

The theoretical and experimental study of the two-neutrino double-beta decay (2νββ-decay) is of crucial importance for reliable calculation of matrix elements governing the neutrinoless double-beta decay (0νββ-decay). That will allow to determine masses of neutrinos once the 0νββ-decay, which occurs if the neutrino is a massive Majorana particle and the total lepton number is not onserved, will be observed. Experiments studying the 2νββ-decay are currently approaching a qualitatively new level, where high-precision measurements are performed not only for half-lives but for all other observables of the process. In this context an improved formula for the 2νββ-decay is presented. Further, a novel approach for determining the effective axial-vector coupling constant is proposed.

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THE ELECTRON ASYMMETRY IN THE BETA DECAY OF POLARIZED NEUTRONS

Canadian Journal of Physics ◽

10.1139/p61-002 ◽

1961 ◽

Vol 39 (1) ◽

pp. 13-21 ◽

Cited By ~ 18

Author(s):

M. A. Clark ◽

J. M. Robson

Keyword(s):

Angular Correlation ◽

Beta Decay ◽

Axial Vector ◽

Coupling Constants ◽

Neutron Spin ◽

Neutron Decay ◽

Vector Coupling ◽

Polarized Neutrons ◽

Spin Direction

The coefficient of the angular correlation between the electron direction and the neutron spin direction in the beta decay of the neutron has been measured using a beam of polarized neutrons. The coefficient of this correlation is −0.09 ± 0.05. This implies that CA/CV, the ratio of the axial vector to vector coupling constants in neutron decay, is equal to −1.20 ± 0.12.

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Neutrinoless double beta decay and neutrino mass

International Journal of Modern Physics E ◽

10.1142/s0218301316300071 ◽

2016 ◽

Vol 25 (11) ◽

pp. 1630007 ◽

Cited By ~ 111

Author(s):

J. D. Vergados ◽

H. Ejiri ◽

F. Šimkovic

Keyword(s):

Beta Decay ◽

Neutrino Mass ◽

Particle Physics ◽

Nuclear Physics ◽

Axial Vector ◽

Neutrinoless Double Beta Decay ◽

Mass Scale ◽

Double Beta Decay ◽

Experimental Point ◽

Vector Coupling

The observation of neutrinoless double beta decay (DBD) will have important consequences. First it will signal that lepton number is not conserved and the neutrinos are Majorana particles. Second, it represents our best hope for determining the absolute neutrino mass scale at the level of a few tens of meV. To achieve the last goal, however, certain hurdles have to be overcome involving particle, nuclear and experimental physics. Particle physics is important since it provides the mechanisms for neutrinoless DBD. In this review, we emphasize the light neutrino mass mechanism. Nuclear physics is important for extracting the useful information from the data. One must accurately evaluate the relevant nuclear matrix elements (NMEs), a formidable task. To this end, we review the recently developed sophisticated nuclear structure approaches, employing different methods and techniques of calculation. We also examine the question of quenching of the axial vector coupling constant, which may have important consequences on the size of the NMEs. From an experimental point of view it is challenging, since the life times are extremely long and one has to fight against formidable backgrounds. One needs large isotopically enriched sources and detectors with good energy resolution and very low background.

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Search for neutrinoless double beta decay

Modern Physics Letters A ◽

10.1142/s0217732316300172 ◽

2016 ◽

Vol 31 (18) ◽

pp. 1630017 ◽

Cited By ~ 14

Author(s):

Igor Ostrovskiy ◽

Kevin O’Sullivan

Keyword(s):

Beta Decay ◽

New Technologies ◽

Axial Vector ◽

Neutrinoless Double Beta Decay ◽

Double Beta Decay ◽

Coupling Constant ◽

Vector Coupling ◽

Axial Vector Coupling ◽

Discovery Potential ◽

Potential Synergy

We review current experimental efforts to search for neutrinoless double beta decay [Formula: see text]. A description of the selected leading experiments is given and the strongest recent results are compared in terms of achieved background indexes (BI) and limits on effective Majorana mass. A combined limit is also shown. The second part of the review covers next generation experiments, highlighting the challenges and new technologies that may be necessary to achieve a justifiable discovery potential. A potential synergy with direct dark matter searches, which could be an especially prudent strategy in case the axial vector coupling constant is quenched in [Formula: see text] decay, is emphasized.

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