25 research outputs found
Quest for double beta decay of 160-Gd and Ce isotopes
The double beta decay study of 160-Gd has been performed in the Solotvina
Underground Laboratory with the help of Gd_2SiO_5(Ce) crystal scintillator
(volume 95 cc). The background of the detector in the vicinity of the 2 beta
energy of 160-Gd was reduced to 1.0 cpd/keV kg. The new improved half-life
limits have been established for neutrinoless 2 beta decay of 160-Gd to the
ground and first excited levels of 160-Dy: T1/2 > 2.3(1.3)E21 yr at 68%(90%)
C.L. The T1/2 bounds have been also set for two neutrino mode as well as for 2
beta decay with Majorons emission. Also the limits were established for
different 2 beta decay processes in 136-Ce, 138-Ce and 142-Ce.Comment: 12 pages, 6 figures, submitted to Nucl. Phys.
New limits on di-nucleons decay into invisible channels
Data of the radiochemical experiment [E.L.Fireman, 1978] with 1.7 t of
KC_2H_3O_2, accumulated deep underground during ~1 yr, were reanalyzed to set
limits on di-nucleons (nn and np) decays into invisible channels
(disappearance, decay into neutrinos, etc.). The obtained lifetime bounds
tau_np > 2.1 10^25 yr and tau_nn > 4.2 10^25 yr (at 90% C.L.) are better (or
competitive) than those established in the recent experiments.Comment: 3 pages, accepted in JETP Letter
Investigation of β + β + and β + /EC decay of 106 Cd
A low background scintillation detector with a CdWO4 crystal of 1.046 kg was used to search for β+β+ and β+/EC processes in 106Cd. For the neutrinoless mode the limits T1/2(0νβ+β+) ≥ 2.2 · 1019 y and T1/2(0νβ+/EC) ≥ 5.5 · 1019 y were obtained with 90% C.L. For the possible two neutrino decay limits of T1/2(2νβ+β+) ≥ 9.2 · 1017 y and 1/2(2νβ+/EC) ≥ 2.6 · 1017 y have been determined with 99% C.L
New results of 116Cd double beta decay study with 116CdWO4 scintillators
A new phase of 116Cd double beta decay experiment is in progress in the
Solotvina Underground Laboratory. Four enriched 116CdWO4 scintillators with
total mass 339 g are used in a set up, whose active shield is made of 15
natural CdWO4 crystals (20.6 kg). The background rate in the energy interval
2.5-3.2 MeV is 0.03 counts/y*kg*keV. The half-life for 2-neutrino 2-beta decay
of 116Cd is measured as T{1/2}(2-neutrino) =
[2.6+-0.1(stat)-0.4+0.7}(syst)]*10**19 y. The T{1/2} limits for neutrinoless
2-beta decay of 116Cd are set as T{1/2} >= 0.7(2.5)*10**23 y at 90%(68%) C.L.
for transition to ground state of 116Sn, while for decays to the first 2+ and
second 0+ excited levels of 116Sn as T{1/2}>=1.3(4.8)*10**22 y and
>=0.7(2.4)*10**22 y with 90%(68%) C.L., respectively. For 0-neutrino 2-beta
decay with emission of one or two Majorons, the limits are T{1/2}(0-neutrino
M1) >=3.7(5.8)*10**21 y and T{1/2}(0-neutrino M2)>=5.9(9.4)*10**20 y at
90%(68%) C.L. Restrictions on the value of the neutrino mass, right-handed
admixtures in the weak interaction, and the neutrino-Majoron coupling constant
are derived as: m(neutrino)<=2.6(1.4) eV, eta <=3.9*10**-8, lambda
<=3.4*10**-6, and g{M}<= 12(9.5)*10**-5 at 90%(68%) C.L., respectively.Comment: 28 pages, 9 figures (LaTeX). Phys. Rev. C (in press
High sensitivity GEM experiment on double beta decay of 76-Ge
The GEM project is designed for the next generation 2 beta decay experiments
with 76-Ge. One ton of ''naked'' HP Ge detectors (natural at the first GEM-I
phase and enriched in 76-Ge to 86% at the second GEM-II stage) are operating in
super-high purity liquid nitrogen contained in the Cu vacuum cryostat (sphere
with diameter 5 m). The latest is placed in the water shield. Monte Carlo
simulation evidently shows that sensitivity of the experiment (in terms of the
T1/2 limit for neutrinoless 2 beta decay) is 10^27 yr with natural HP Ge
crystals and 10^28 yr with enriched ones. These bounds corresponds to the
restrictions on the neutrino mass less than 0.05 eV and 0.015 eV with natural
and enriched detectors, respectively. Besides, the GEM-I set up could advance
the current best limits on the existence of neutralinos - as dark matter
candidates - by three order of magnitudes, and at the same time would be able
to identify unambiguously the dark matter signal by detection of its seasonal
modulation.Comment: LaTeX, 20 pages, 4 figure
The Majorana neutrino masses, neutrinoless double beta decay and nuclear matrix elements
The effective Majorana neutrino mass is evaluated by using the latest results
of neutrino oscillation experiments. The problems of the neutrino mass
spectrum,absolute mass scale of neutrinos and the effect of CP phases are
addressed. A connection to the next generation of the neutrinoless double beta
decay (0nbb-decay) experiments is discussed. The calculations are performed for
76Ge, 100Mo, 136Xe and 130Te by using the advantage of recently evaluated
nuclear matrix elements with significantly reduced theoretical uncertainty. An
importance of observation of the 0nbb-decay of several nuclei is stressed.Comment: 29 pages, 5 figures, EXO (10 t) experiment considere
Double Beta Decay
We review recent developments in double-beta decay, focusing on what can be
learned about the three light neutrinos in future experiments. We examine the
effects of uncertainties in already measured neutrino parameters and in
calculated nuclear matrix elements on the interpretation of upcoming
double-beta decay measurements. We then review a number of proposed
experiments.Comment: Some typos corrected, references corrected and added. A less blurry
version of figure 3 is available from authors. 41 pages, 5 figures, submitted
to J. Phys.