Neutrinoless double-electron capture Blaum, K.; Eliseev, S.; Danevich, F. A. ...
Reviews of modern physics,
12/2020, Letnik:
92, Številka:
4
Journal Article
Recenzirano
Odprti dostop
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.
Two-neutrino double
β
decay can create an irremovable background even in high energy resolution detectors searching for neutrinoless double
β
decay due to random coincidence of 2
ν
2
β
events in the ...case of poor time resolution. Some possibilities for suppressing this background in cryogenic scintillating bolometers are discussed. It is shown that the present bolometric detector technologies enable one to control this form of background at the level required to explore the inverted hierarchy of the neutrino mass pattern, including the case of bolometers searching for the neutrinoless double
β
decay of
100
Mo, which is characterized by a relatively short two-neutrino double
β
decay half-life.
We report the development of a CaMoO4 crystal low temperature detector for the AMoRE neutrinoless double beta decay ( 0 ν β β ) search experiment. The prototype detector cell was composed of a 216 g ...CaMoO4 crystal and a metallic magnetic calorimeter. An overground measurement demonstrated FWHM resolution of 6–11 keV for full absorption gamma peaks. Pulse shape discrimination was clearly demonstrated in the phonon signals, and 7.6 σ of discrimination power was found for the α and β / γ separation. The phonon signals showed rise-times of about 1 ms. It is expected that the relatively fast rise-time will increase the rejection efficiency of two-neutrino double beta decay pile-up events which can be one of the major background sources in 0 ν β β searches.
The resonance excitation of the 7Li nuclei in a LiF crystal with mass of 553 g by hypothetical axions emitted in the deexcitation of the 7Li nuclei in the Sun was searched for deep underground at the ...Gran Sasso National Laboratories (LNGS) of INFN (3600 m w.e.). The data collected with a low background HP Ge detector 244 cm3 during 4044h have allowed us to set the limit on the axion mass: ma<8.6 keV (90% C.L.) which is the best one for the 7Li solar axions to-date.
A
bstract
Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing ...at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei
100
Mo and
130
Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of
α
surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li
2
MoO
4
and TeO
2
. We have also shown that point-like energy depositions can be identified up to a distance of
∼
1 mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising
∼
3
×
10
25
nuclei of
100
Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.
In the anisotropic scintillators the light output and the pulse shape for heavy particles (
p
,
α
, nuclear recoils) depend on the direction with respect to the crystal axes; the response to
γ
/
β
...radiation is isotropic instead. This feature offers the possibility to study the directionality approach, which is applicable in the particular case of those Dark Matter candidate particles inducing just nuclear recoils. Among the anisotropic scintillators, the ZnWO
4
has unique features, which make it an excellent candidate for this type of research, and there is still plenty of room for the improvement of its performances. In this paper the possibility of a low background pioneer experiment (named ADAMO—Anisotropic detectors for DArk Matter Observation) to exploit deep underground the directionality approach by using anisotropic ZnWO
4
scintillators is discussed.
.
The current status of the experimental searches for rare alpha and beta decays is reviewed. Several interesting observations of alpha and beta decays, previously unseen due to their large ...half-lives (
10
15
-
10
20
yr), have been achieved during the last years thanks to the improvements in the experimental techniques and to the underground locations of experiments that allows to suppress backgrounds. In particular, the list includes first observations of alpha decays of
151
Eu ,
180
W (both to the ground state of the daughter nuclei),
190
Pt (to excited state of the daughter nucleus),
209
Bi (to the ground and excited states of the daughter nucleus). The isotope
209
Bi has the longest known half-life of
T
1
/
2
≈
10
19
yr relatively to alpha decay. The beta decay of
115
In to the first excited state of
115
Sn (
E
exc
=
497
.
334
keV), recently observed for the first time, has the
Q
β
value of only
(
147
±
10
)
eV, which is the lowest
Q
β
value known to-date. Searches and investigations of other rare alpha and beta decays (
48
Ca ,
50
V,
96
Zr,
113
Cd,
123
Te,
178m2
H,
180m
Ta and others) are also discussed.
A multi-isotope 0 ν 2 β bolometric experiment Giuliani, A; Danevich, F A; Tretyak, V I
The European physical journal. C, Particles and fields,
03/2018, Letnik:
78, Številka:
3
Journal Article
Recenzirano
Odprti dostop
There are valuable arguments to perform neutrinoless double beta (0ν2β) decay experiments with several nuclei: the uncertainty of nuclear-matrix-element calculations; the possibility to test these ...calculations by using the ratio of the measured lifetimes; the unpredictability of possible breakthroughs in the detection technique; the difficulty to foresee background in 0ν2β decay searches; the limited amount of isotopically enriched materials. We propose therefore approaches to estimate the Majorana neutrino mass by combining experimental data collected with different 0ν2β decay candidates. In particular, we apply our methods to a next-generation experiment based on scintillating and Cherenkov-radiation bolometers. Current results indicate that this technology can effectively study up to four different isotopes simultaneously (82Se, 100Mo, 116Cd and 130Te), embedded in detectors which share the same concepts and environment. We show that the combined information on the Majorana neutrino mass extracted from a multi-candidate bolometric experiment is competitive with that achievable with a single isotope, once that the cryogenic experimental volume is fixed. The remarkable conceptual and technical advantages of a multi-isotope investigation are discussed. This approach can be naturally applied to the proposed CUPID project, follow-up of the CUORE experiment that is currently taking data in the Gran Sasso underground laboratory.
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