Abstract
The CROSS experiment is proposing to use a new technology of surface sensitive bolometers for low-background neutrinoless double beta decay searches. Efficient rejection of surface
α
and
β
...events will allow to reach background in the region of interest below than 10
−4
cnts/keV/kg/yr. The isotopes of interest, which are
130
Te and
100
Mo, are investigated with TeO
2
and Li
2
MoO
4
bolometers. The surface sensitivity is achieved thanks to the evaporation of thin metallic film on the crystal surface that modifies the pulse shape of near-surface events. An investigation of various pulse shape parameters was performed. The analysis shows that one of the best parameters for discrimination is the integrated area of the raw signal both for TeO
2
and Li
2
MoO
4
with Pd-Al (10 nm - 100 nm) bi-layer.
Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino ...double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of 100Mo to the ground state of 100Ru of 7.07±0.02(stat)±0.11(syst)×1018 yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in 100Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ3,1=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. Finally, we also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.
The CUPID-Mo experiment, located at Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20 Li2 100MoO4 (LMO) calorimeters each equipped ...with a Ge light detector (LD) for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double beta decays of 100Mo to the first 0+ and 2+ excited states of 100Ru using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2νββ decay to the $0^+_1$ state as $T^{2ν→0^+_1}_{1/2}$ = (7.5 ± 0.8 (stat.) $^{+0.4}_{-0.3}$ (syst.)) × 1020 yr. The bolometric technique enables measurement of the electron energies as well as the gamma rays from nuclear de-excitation and this allows us to set new limits on the two-neutrino decay to the $2^+_1$ state of $T^{2ν→2^+_1}_{1/2}$ > 4.4×1021 yr (90% c.i.) and on the neutrinoless modes of $T^{0ν→2^+_1}_{1/2}$ > 2.1×1023 yr (90% c.i.), $T^{0ν→0^+_1}_{1/2}$ > 1.2 × 1023 yr (90% c.i.). Information on the electrons spectral shape is obtained which allows us to make the first comparison of the single state (SSD) and higher state (HSD) 2νββ decay models for the $0^+_1$ excited state of 100Ru.
The NEMO-3 results for the double-
β
decay of
150
Nd to the 0
1
+
and 2
1
+
excited states of
150
Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope
150
Nd are used in the ...analysis. The signal of the
2
ν
β
β
transition to the 0
1
+
excited state is detected with a statistical significance exceeding 5
σ
. The half-life is measured to be
T
1
/
2
2
ν
β
β
(
0
1
+
)
=
1
.
11
-
0.14
+
0.19
stat
-
0.15
+
0.17
syst
×
10
20
year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the
2
ν
β
β
decay to the 2
1
+
level the limit is
T
1
/
2
2
ν
β
β
(
2
1
+
)
>
2.42
×
10
20
year
. The limits on the
0
ν
β
β
decay to the 0
1
+
and 2
1
+
levels of
150
Sm are significantly improved to
T
1
/
2
0
ν
β
β
(
0
1
+
)
>
1.36
×
10
22
year
and
T
1
/
2
0
ν
β
β
(
2
1
+
)
>
1.26
×
10
22
year
.
The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale bolometric 0νββ experiment. It consists of a 4.2 kg array of 20 ...enriched Li2 100MoO4 scintillating bolometers to search for the lepton-number-violating process of 0νββ decay in 100Mo. With more than one year of operation (100Mo exposure of 1.17 kg × yr for physics data), no event in the region of interest and, hence, no evidence for 0νββ is observed. We report a new limit on the half-life of 0νββ decay in 100Mo of T1/2 > 1.5 × 1024 yr at 90% C.I. The limit corresponds to an effective Majorana neutrino mass ⟨m β β⟩ < (0.31 –0.54 ) eV, dependent on the nuclear matrix element in the light Majorana neutrino exchange interpretation.
The double-beta decay of Cd116 has been investigated with the help of radiopure enriched Cd116WO4 crystal scintillators (mass of 1.162 kg) at the Gran Sasso underground laboratory. The half-life of ...Cd116 relative to the 2ν2β decay to the ground state of Sn116 was measured with the highest up-to-date accuracy as T1/2=(2.63−0.12+0.11)×1019 yr. A new improved limit on the 0ν2β decay of Cd116 to the ground state of Sn116 was set as T1/2≥2.2×1023 yr at 90% C.L., which is the most stringent known restriction for this isotope. It corresponds to the effective Majorana neutrino mass limit in the range ⟨mν⟩≤(1.0–1.7) eV, depending on the nuclear matrix elements used in the estimations. New improved half-life limits for the 0ν2β decay with majoron(s) emission, Lorentz-violating 2ν2β decay, and 2β transitions to excited states of Sn116 were set at the level of T1/2≥1020–1022 yr. New limits for the hypothetical lepton-number violating parameters (right-handed currents admixtures in weak interaction, the effective majoron-neutrino coupling constants, R-parity violating parameter, Lorentz-violating parameter, heavy neutrino mass) were set.
PDF
