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.
Semi-empirical method of calculation of quenching factors for scintillators is described. It is based on classical Birks formula with the total stopping powers for electrons and ions which are ...calculated with the ESTAR and SRIM codes, respectively. Method has only one fitting parameter (the Birks factor
kB) which can have different values for the same material in different conditions of measurements and data treatment. A hypothesis is used that, once the
kB value is obtained by fitting data for particles of one kind and in some energy region (e.g. for a few MeV
α
particles from internal contamination of a detector), it can be applied to calculate quenching factors for particles of another kind and for another energies (e.g. for low energy nuclear recoils) if all data are measured in the same experimental conditions and are treated in the same way. Applicability of the method is demonstrated on many examples including materials with different mechanisms of scintillation: organic scintillators (solid
C
8
H
8
, and liquid
C
16
H
18
,
C
9
H
12
); crystal scintillators (pure
CdWO
4
,
PbWO
4
,
ZnWO
4
,
CaWO
4
,
CeF
3
, and doped
CaF
2
(Eu), CsI(Tl), CsI(Na), NaI(Tl)); liquid noble gases (LXe). Estimations of quenching factors for nuclear recoils are also given for some scintillators where experimental data are absent (
CdWO
4
,
PbWO
4
,
CeF
3
,
Bi
4
Ge
3
O
12
, LiF, ZnSe).
Nuclear decays with simultaneous emission of two alpha particles are energetically possible for a number of nuclides. Prospects of searching for such kind of decay for nuclides present in the natural ...isotopic composition of elements are discussed here. The first experimental limit on half-life for 2α decay is set for 209Bi as T1/2 > 2.9·1020 y at 90 % C.L., using the data of work P. de Marcillac et al. Nature 422 (2003) 876. Theoretical T1/2 estimations for the process are also given. Using these values, which are on the level of 1033 y or more, one can conclude that the prospects of experimental observation of 2α decay are very pessimistic.
The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay (
0
ν
β
β
) of
100
Mo with
∼
100
kg
of
100
Mo-enriched molybdenum embedded in cryogenic ...detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from
48
Ca-depleted calcium and
100
Mo-enriched molybdenum (
48
depl
Ca
100
MoO
4
). The simultaneous detection of heat (phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot
0
ν
β
β
search with a 111 kg day live exposure of
48
depl
Ca
100
MoO
4
crystals. No evidence for
0
ν
β
β
decay of
100
Mo is found, and a upper limit is set for the half-life of
0
ν
β
β
of
100
Mo of
T
1
/
2
0
ν
>
9.5
×
10
22
years
at 90% C.L. This limit corresponds to an effective Majorana neutrino mass limit in the range
⟨
m
β
β
⟩
≤
(
1.2
-
2.1
)
eV
.
The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of Formula omittedMo to the ground state of Formula omittedRu, Formula omitted ...year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of Formula omitted events and a signal-to-background ratio of Formula omitted 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of Formula omitted, as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.
CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay (
0
ν
β
β
) of
100
Mo
. In this article, we detail the CUPID-Mo detector concept, assembly and installation in the ...Modane underground laboratory, providing results from the first datasets. The CUPID-Mo detector consists of an array of 20
100
Mo
-enriched 0.2 kg
Li
2
MoO
4
crystals operated as scintillating bolometers at
∼
20
mK
. The
Li
2
MoO
4
crystals are complemented by 20 thin Ge optical bolometers to reject
α
events by the simultaneous detection of heat and scintillation light. We observe a good detector uniformity and an excellent energy resolution of 5.3 keV (6.5 keV) FWHM at 2615 keV, in calibration (physics) data. Light collection ensures the rejection of
α
particles at a level much higher than 99.9% – with equally high acceptance for
γ
/
β
events – in the region of interest for
100
Mo
0
ν
β
β
. We present limits on the crystals’ radiopurity:
≤
3
μ
Bq/kg
of
226
Ra
and
≤
2
μ
Bq/kg
of
232
Th
. We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the
100
Mo
0
ν
β
β
decay in half-a-year’s livetime. The achieved results show that CUPID-Mo is a successful demonstrator of the technology developed by the LUMINEU project and subsequently selected for the CUPID experiment, a proposed follow-up of CUORE, the currently running first tonne-scale bolometric
0
ν
β
β
experiment.
A long-term measurement was conducted to search for α, double-α and double-β decays with γ quanta emission in naturally occurring osmium isotopes. This study took advantage of two ultra-low ...background HPGe detectors and one ultra-low background BEGe detector at the Gran Sasso National Laboratory (LNGS) of the INFN. Over almost 5 years of data were taken using high-purity osmium samples of approximately 173 g. The half-life limits set for α decays of
184
Os to the first 2
+
103.6 keV excited level of
180
W (
T
1/2
≥ 9.3 × 10
15
yr) and of
186
Os to the first 2
+
100.1 keV of
182
W (
T
1/2
≥ 4.8 × 10
17
yr) exceed substantially the present theoretical predictions that are at level of
T
1/2
~ (0.6–3) × 10
15
yr for
184
Os and
T
1/2
~ (0.3–2) × 10
17
yr for
186
Os. New half-life limits on the 2EC and ECβ
+
decay of
184
Os to the ground and excited levels of
184
W were set at level of
T
1/2
> 10
16
–10
17
yr; a lower limit on the 2β
–
decay of
192
Os to the 2
+
316.5 keV excited level of
192
Pt was estimated as
T
1/2
≥ 6.1 × 10
20
yr. The half-life limits for 2α decay of
189
Os and
192
Os were set for the first time at level of
T
1/2
> 10
20
yr.
.
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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