Nucl.Phys.A781:209-226,2007 The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru
is studied using the NEMO 3 data. After the analysis of 8024 h of data the
half-life for the ...two-neutrino double beta decay of 100Mo to the excited 0^+_1
state is measured to be T^(2nu)_1/2 = 5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)x
10^20 y. The signal-to-background ratio is equal to 3. Information about energy
and angular distributions of emitted electrons is also obtained. No evidence
for neutrinoless double beta decay to the excited 0^+_1 state has been found.
The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y
(at 90% C.L.).
The search for the double beta decay to the 2^+_1 excited state has allowed
the determination of limits on the half-life for the two neutrino mode
T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the
neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).
Nucl.Instrum.Meth.A503:649-657,2003 The background induced by radioactive impurities of $^{208}\rm Tl$ and
$^{214}\rm Bi$ in the source of the double beta experiment NEMO-3 has been
investigated. New ...methods of data analysis which decrease the background from
the above mentioned contamination are identified. The techniques can also be
applied to other double beta decay experiments capable of measuring
independently the energies of the two electrons.
The interest and relevance of next-generation 0
v
ββ-decay experiments is increasing. Even with nonzero neutrino mass strongly suggested by solar and atmospheric neutrino experiments sensitive to
δm
...2, 0
v
ββ-decay experiments are still the only way to establish the Dirac or Majorana nature of neutrinos by measuring the effective electron neutrino mass, 〈
m
v
〉. In addition, the atmospheric neutrino oscillation experiments imply that at least one neutrino has a mass greater than about 50 meV. The Majorana Experiment expects to probe an effective neutrino mass near this critical value.
Majorana is a next-generation
76Ge double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in
76Ge, in the form of ∼ 200 detectors in a close-packed array. Each crystal will be electronically segmented and each segment fitted with pulse-shape analysis electronics. This combination of segmentation and pulse-shape analysis significantly improves our ability to discriminate neutrinoless double beta-decay from internal cosmogenic
68
Ge and
60
Co. The half-life sensitivity is estimated to be 4.2 × 10
27 y corresponding to a 〈
m
v
〉 range of ≤ 20 − 70 meV, depending on the nuclear matrix elements used to interpret the data.
The Majorana Experiment is a next-generation Ge-76 double-beta decay search.
It will employ 500 kg of Ge, isotopically enriched to 86% in Ge-76, in the form
of 200 detectors in a close-packed array ...for high granularity. Each crystal
will be electronically segmented, with each region fitted with pulse-shape
analysis electronics. A half-life sensitivity is predicted of 4.2e27 y or
< 0.02-0.07 eV, depending on the nuclear matrix elements used to
interpret the data.
The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta ...decay of 100Mo to the excited 0^+_1 state is measured to be T^(2nu)_1/2 = 5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)x 10^20 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0^+_1 state has been found. The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y (at 90% C.L.). The search for the double beta decay to the 2^+_1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).
The background induced by radioactive impurities of \(^{208}\rm Tl\) and \(^{214}\rm Bi\) in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which ...decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.
The Majorana Experiment is a next-generation Ge-76 double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in Ge-76, in the form of 200 detectors in a close-packed array ...for high granularity. Each crystal will be electronically segmented, with each region fitted with pulse-shape analysis electronics. A half-life sensitivity is predicted of 4.2e27 y or < 0.02-0.07 eV, depending on the nuclear matrix elements used to interpret the data.
From data accumulated over 6140 h with 172 g of enriched molybdenum (1.18 mol yr of sup 100Mo) with the NEMO 2 detector in the Frejus Underground Laboratory, a clear betabeta2nu signal (1433 events) ...is observed, leading to a half-life ital Tsub 1/2=0.95plus minus0.04(stat)plus minus0.09(syst) 10sup 19 yr. The experimental two-electron energy spectrum and the two-electron angular distribution are in agreement with the expected ones. Limits for betabeta0nu decays to the ground state, excited states (2sub 1sup + and 0sub 1sup +), and also with Majoron emission are given.
![Two-neutrino double-[beta] ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0556-2821/small "Two-neutrino double-[beta] decay measurement of [sup 100]Mo")