If an experiment works, something has gone wrong
Finagle's First Law
(see also: International collaboration)
All limits below correspond to 90% Confidence Level, if not stated explicitly otherwise. For references, see publications of the LPD group. The abbreviation «UL» below is for Underground Laboratory.
1. First observation of the two-neutrino 2β decay of 116Cd. The LPD group took part in all four experiments, based on different experimental technique, where 2β2ν decay of 116Cd was observed at the first time and the T1/2 value and energy and angular distributions of the electrons were measured:
(1) measurements with the ELEGANTS-V set-up (Kamioka UL, Japan, 1875 h; T1/2 = 2.6+0.9-0.5×1019 yr [4(1994), 9(1995)]);
(2) measurements with the tracking detector NEMO-2 (Frejus UL, France, 6588 h; T1/2 = 3.8±0.4×1019 yr [6(1995), 10(1996)]);
(3) experiment with isotopically enriched scintillator 116CdWO4 (83% of 116Cd, Solotvina UL, Ukraine, 13316 h of measurements in the last modification of the set-up; T1/2 = 2.9+0.4-0.3×1019 yr [1(1995), 2(2000), 3(2003)]);
(4) the half-life of 116Cd relatively to the two-neutrino double beta decay is measured with the highest up-to-date accuracy Aurora experiment with isotopically enriched scintillator 116CdWO4 [11(2011)] (82% of 116Cd, Gran Sasso UL, Italy, 12015 h of measurements in the last modification of the set-up; T1/2 = 2.62±0.14×1019 yr [35(2015), 26(2016)])
2. Lower limits on T1/2 for neutrinoless modes of 116Cd 2β decay.
(1) The limits on 2β0ν decay of 116Cd and decays with emission of one or two Majorons, determined with the 116CdWO4, are the most stringent to-date limits for this nucleus [3(2003)]:
T1/2(0ν, g.s.) ≥ 1.7×1023 yr,
T1/2(0ν, 2+1) ≥ 2.9×1022 yr,
T1/2(0ν, 0+1) ≥ 1.4×1022 yr,
T1/2(0νM1) ≥ 8.0×1021 yr,
T1/2(0νM2) ≥ 8.0×1020 yr,
T1/2(0νMbulk) ≥ 1.7×1021 yr.
The value of 1.7×1023 yr was fifth world result (after 76Ge, 136Xe, 130Te, 100Mo) for T1/2 limits, determined for all known 2β candidates. The upper limits on the neutrino mass (mν ≤ 1.7 eV), right-handed admixtures in the weak currents, neutrino-Majoron coupling constant and other theoretical parameters were calculated. Full time of measurements with the 116CdWO4 detector(s) in the Solotvina UL is near 60 000 h.
(2) The Aurora experiment is in progress to investigate 2β processes in 116Cd by using enriched
116CdWO4 scintillation detectors [11(2011)].
The new improved 2β0ν half-life limit is set as T1/2(0ν, g.s.) ≥ 1.9×1023 yr, at 90% CL after 12015 h of data taking, which corresponds to the effective Majorana neutrino mass mν ≤ (1.2-1.8) eV. New limits on the 2β decay to excited levels of 116Sn and the 0ν decay with emission of one, two and bulk majorons were set at the level of T1/2 > (1020 - 1022) yr [35(2015), 26(2016)].
3. Participation in the experiments with the NEMO collaboration to study 2β decays of 82Se, 94Zr, 96Zr and 100Mo. In the experiments with the tracking detector NEMO-2 (Frejus UL, France) the existence of 2β2ν decays of 82Se, 96Zr and 100Mo was confirmed, and half-lives and energy and angular distributions of emitted electrons were measured:
100Mo - 6140 h, T1/2 = 9.5±1.0×1018 yr
82Se - 10357 h, T1/2 = 8.3±1.1×1019 yr [4(1998)];
96Zr - 10357 h, T1/2 = 2.1+0.8-0.4×1019 yr [6(1999)] (this is the first observation of 96Zr 2β2ν decay in direct experiment).
The lower limits on 2β decays of 94Zr were established [6(1999)] (T1/2 ≥ 1×1017 - 2×1019 yr for different modes, which are the best known limits for this nucleus).
4. Search for 2β decay of 106Cd. Experiments were performed (in progress) in the Gran Sasso UL, Italy:
(1) with big (1.046 kg) CdWO4 crystal (6701 h, T1/2(2β+0ν) ≥ 2.2×1019 yr and T1/2(εβ+0ν) ≥ 5.5×1019 yr) [9(1996)];
(2) with two NaI detectors and enriched (68%) 106Cd sample (4321 h, for different modes of 2β+, εβ+ and 2ε decays T1/2 ≥ (0.3-4)×1020 yr, which are 6 to 60 times better than determined in other experiments) [1(1999)];
(3) by using cadmium tungstate crystal scintillator enriched (66%) in 106Cd [6(2010)]. The limits on the level of T1/2 ≥ (0.08-4.1)×1020 yr were obtained for different modes of 2β+, εβ+ and 2ε decays [21(2010), 19(2011), 4(2012)]. The experiment is in progress.
(4) by using the enriched 106CdWO4 crystal scintillator in coincidence with four crystal HPGe detector. New improved limits on the double beta processes in 106Cd have been set on the level of 1020-1021 yr after 13085 h of data taking [2(2014), 6(2015), 31(2015), 30(2016), 3(2016)]
5. Precise measurement of two-neutrino 2β decay of 100Mo to the first 0+ excited level of 100Ru by HP Ge γ spectrometry with the half-life T1/2= 6.9+1.0-0.8(stat.)±0.7(syst.)×1020 yr (in the ARMONIA experiment performed in the Gran Sasso UL, Italy [3(2010)]), and with the half-life T1/2= 7.5±0.6(stat.)±0.6(syst.)×1020 yr (in the NEMO experiment at the Modane UL, France [2(2014)]).
6. Search for 2β decay of 96Ru and 104Ru with HP Ge γ spectrometry on the level of sensitivity T1/2 ≥ 1018-1019 yr [3(2009), 13(2010), 4(2013)]
7. First search for 2β decay of 156Dy and 158Dy with HP Ge γ spectrometry on the level of sensitivity T1/2 ≥ 1015-1017 yr [7(2011)].
8. Search for 2β decay of 190,198Pt and 184,192Os with HP Ge γ spectrometry on the level of sensitivity T1/2 ≥ 1014-1019 yr [8(2011), 3(2013)].
9. Search for 2β decays of 108Cd, 114Cd, 180W, 186W. The experimental limits on 2β decays of these nuclei (Solotvina UL, 116CdWO4 and CdWO4 scintillators) were determined at the first time and are in the range of T1/2 ≥ 6.0×1016 yr to T1/2 ≥ 1.1×1021 yr (the best up-to-date limits) [4(1995), 3(2003), 4(2003)]. The experimental sensitivity was then improved in the experimants at the Gran Sasso UL by using low-background CdWO4 and ZnWO4 crystal scintillaotrs [7(2008), 2(2009)].
10. Search for 2β processes in 64Zn, 70Zn, 180W and 186W was perforemd with low-background ZnWO4 crystal scintillators (Gran Sasso UL) on the level of sensitivity T1/2 ≥ 1017-1021 yr [1(2008), 2(2009), 5(2011)].
11. Limits on 2β decays of 40Ca, 46Ca. In the experiment with two CaF2 detectors with mass of 370 g each (Gran Sasso UL, Italy, 1906 h), the limits on 2ε decays of 40Ca (T1/2 ≥ (3.0-5.9)×1021 yr, these are the record values for the limits on probability of 2ε decay for all nuclei-candidates) and 2β- decay of 46Ca (T1/2 ≥ 1.0×1017 yr, the best for this nucleus) were determined [5(1999)].
12. Investigation of 2β decays of 160Gd, 136Ce, 138Ce, 142Ce. In the experiment with Gd2SiO5(Ce) detector with mass of 635 g (Solotvina UL, 13949 h), the limit T1/2(2β0ν, 160Gd) ≥ 1.3×1021 yr was established (near one order of magnitude higher than that reached by other groups). The limits on probabilities of 2β processes were established, most of them at the first time, for Ce isotopes:
T1/2(2β+0ν, 136Ce) ≥ 1.9×1016 yr,
T1/2(Kβ+0ν, 136Ce) ≥ 3.8×1016 yr,
T1/2(Kβ+2ν, 136Ce) ≥ 1.8×1015 yr,
T1/2(2K0ν, 136Ce) ≥ 6.0×1015 yr,
T1/2(2K0ν, 138Ce) ≥ 1.8×1015 yr,
T1/2(2β-0ν, 142Ce) ≥ 2.0×1018 yr,
T1/2(2β-2ν, 142Ce) ≥ 1.6×1017 yr [3(2001)].
13. Search for β and 2β decays of 48Ca was performed with CaF2(Eu) scintillator (1.1 kg, 3236 h, Gran Sasso UL, Italy); obtained limits were from T1/2 ≥ 1.2×1018 yr to T1/2 ≥ 5.5×1019 yr [5(2002)].
14. Search for 2β decay of cerium
(1) with CeF3 scintillator (49 g, 2142 h, Gran Sasso UL, Italy) [8(2003)];
(2) comparable limits were obtined in an experiment in the Gran Sasso UL by using CeCl3 crystal scintillator [6(2011)];(3) search for double beta processes in cerium with HPGe gamma spectrometry [11(2014)];
15. Limits on double electron capture in 196Hg.
In measurements with HP Ge detector 165 cm3 (Solotvina UL, 1109 h) the limit on
the probability of two electron (0ν+2ν) capture in 196Hg was established:
T1/2 ≥ 2.5×1018 yr (the best up-to-date result for this nuclide) [1(1990)].
16. Early searches for 2β0ν decays of 96Zr, 100Mo and 130Te on the earth level. In the measurements with plastic scintillator-wafer stacks and enriched in 130Te sheets of tellurium (1100 h), the limit T1/2(130Te) ≥ 1.2×1021 yr (68% CL) was obtained in 1980 [2(1980), 3(1980)]. This value was surpassed only in 1992 in the experiment of the Milano group with TeO2 bolometer. In similar measurements with 100Mo and 96Zr, the limits T1/2(100Mo) ≥ 2.2×1021 yr (90% CL) [1(1983)] and T1/2(96Zr) ≥ 3.0×1019 yr (68% CL) [1(1981)] had been set, also the best at that time.
17. Search for 2β decay of radioactive (β and/or α unstable) nuclides was proposed in [3(2005)]. The possible advantage is higher value of Q2β (up to ~40 MeV) in comparison with «conventional» 2β nuclides (Q2β ≤ 4.3 MeV) which results in higher 2β0ν decay rates because of dependence T1/2-1 ~ Q2β5.
18. Investigation of 4th forbidden non-unique β decay of 113Cd. Only three nuclei (also 9(1995)V and 115In) are known in the nature for which such decay is not hidden by other decay modes; investigations are very laborious because of a big T1/2 values. Shape of 113Cd β spectrum and T1/2 value were measured in the experiment with CdWO4 (Solotvina UL) as T1/2 = 7.7±0.3×1015 yr [2(1996)]. The beta decay was remeasured with higher accuracy at Gran Sasso UL giving T1/2 = 8.04±0.05×1015 yr [2(2007)].
19. Search for α decays of natural tungstate isotopes. The limits on probability of α decay of 182W, 183W, 184W, 186W isotopes were set in the measurements with CdWO4 and 116CdWO4 scintillators in the Solotvina UL in the range of T1/2 ≥ (0.8-1.8)×1020 yr [5(1995), 2(2003)]. First indications for observation of 180W α decay were obtained; measured half-life is T1/2(180W)=1.1+0.9-0.5×1018 yr [2(2003)]. Later it was observed also with CaWO4 (T1/2 = 1.0+0.7-0.3×1018 yr) [5(2005)] and ZnWO4 (T1/2 = 1.3+0.6-0.5×1018 yr) [12(2011)] scintillators.
20. Limit on α decay of 142Ce was established in measurements with CeF3 scintillator (49 g, 2142 h, Gran Sasso UL, Italy) as T1/2(142Ce) ≥ 2.9×1018 yr [8(2003)] (the best value to-date).
21. First observation of α decay of 151Eu was concluded from measurements with CaF2(Eu) crystal scintillator (370 g, 7426 h, Gran Sasso UL, Italy); measured half-life is T1/2(151Eu)=5+11-3×1018 yr [1(2007)].
22. α decay of 190Pt to the excited level (Eexc = 137.2 keV) of 186Os was observed for the first time with the help of ultra-low background spectrometry at the Gran Sasso UL (Italy); measured half-life is T1/2=2.6+0.4-0.3(stat.)±0.6(syst.)×1014 yr [4(2011)].
23. Studies of transitions of Cu, Ti and Hg nuclei to super-dense state. The limits on probability of such processes were established in measurements with HP Ge detector of 165 cm3 (Solotvina UL, 1109 h) on the T1/2 level of 1021-1022 yr [1(1990)].
24. Search for nuclear decay with emission of various clusters. The limits on cluster decays of Hg isotopes were derived from the measurements with HP Ge detector of 165 cm3 (Solotvina UL, 1109 h): for different clusters, from 14C to 69Ni, T1/2 ≥ ~1021 yr [1(1990)]. Limits for 127I were established on the level of up to ~1024 yr [9(2005)] (the most stringent for all known limits on probability of cluster decays); decays of La isotopes were also searched for [10 (2005)] (T1/2 ≥ ~1018-1021 yr).
25. Search for long-lived superheavy ekatungsten with radiopure ZnWO4 crystal scintillator. The data collected with a radioactively pure ZnWO4 crystal scintillator (699 g) in low background measurements during 2130 h at the underground (3600 m w.e.) Laboratori Nazionali del Gran Sasso (INFN, Italy) were used to set a limit on possible concentration of superheavy eka-W (seaborgium Sg, Z = 106) in the crystal at the level of < 5.5 × 10−14 atoms/atom [5(2015)]
26. Limits on the electron stability and electric charge non-conservation. The results are based on the measurements with the DAMA NaI detectors (87.3 kg, 5364 h) and DAMA liquid Xe detector (6.5 kg, 8336 h) in the Gran Sasso UL, Italy. The determined limits on the electron stability (and, hence, on the electric charge conservation) are equal:
τ(e- → νe+γ) ≥ 2.0×1026 yr
τ(e- → νe+νe+νe) ≥ 2.4×1024 yr [2(1999)],
(the last value, valid also for electron disappearance, is the most stringent to-date and higher ~10 times than those known before). The limits on the electron disappearance with excitation of nuclear levels also were established for 23Na, 127I and 129Xe (T1/2≥1.5×1023-4.0×1024 yr, the best known values) [3(1999), 4(1999)]. The bounds on the charge non-conserving admixtures in the weak interactions were determined (εW2 ≤ 2.2×10-26, εγ2 ≤ 1.3×10-42) as well as the upper limit on the mass of γ quantum (mγ ≤ 1.4×10-14 eV).
27. Charge non-conserving (CNC) β decay of 73Ge, 136Xe and 139La. To set limit on 73Ge, data accumulated with 952 g HP Ge detector during 15288 h (Baksan UL, Russia) were used. Instead of traditional in this field radiochemical methods, the real-time approach was used for the first time. First limit for 73Ge CNC β decay was set as τ > 2.6×1023 yr [3(2002)]. Limit for 136Xe was derived from data of the DAMA/LXe experiment (τ > 1.3×1023 yr) [7(2002)]. Measurements with LaCl3 crystal scintillator were used to derive limit on CNC β decay of 139La: τ > 1.0×1018 yr [5(2006)].
28. CNC β decay of 115In.
Limit on the CNC β decay of 115In was set at the first time
with the data of the LENS Collaboration where indium sample of 929 g was
measured with 4 HP Ge detectors ~225 cm3 each during 2762 h:
τ > 4.1×1020 yr. As a very interesting by-product of this search for exotic process, the first experimental observation of usual β decay of 115In to the first excited level of 115Sn has been obtained. This is beta decay with extremelly low probability of 1.2×10-6 (what corresponds to T1/2=3.7×1020 yr) and, possibly, with the lowest known value of Qβ (of ~500 eV) [4(2005), 9(2007)].
29. Search for the nucleon, di-nucleon and tri-nucleon decay into invisible channels. A new scheme was proposed to search for disappearance or decay into invisible channels of nucleons in atomic nuclei, when the decay of a daughter nucleus, incorporated into detector, is looked for [3(2000)]. Limits were established first on the base of the data with the DAMA liquid Xe detector (6.5 kg, 8336 h, Gran Sasso UL, Italy) [3(2000)], and then were improved with the BOREXINO Counting Test Facility (liquid scintillator, 4.2 t, 626 h, Gran Sasso UL, Italy) to the following values:
τp ≥ 1.1×1026 yr,
τn ≥ 1.8×1025 yr,
τpp ≥ 5.0×1025 yr,
τnn ≥ 4.9×1025 yr
(the last two were the best known limits) [5(2003)]. Reanalysing data of old radiochemical experiment, the limit
τnp > 2.1×1025 yr
was established (the best to-date) [1(2004)]. Tri-nucleon disappearance was looked for at the first time too [6(2006)]:
τnnp ≥ 1.4×1022 yr,
τnpp ≥ 2.7×1022 yr,
τppp ≥ 3.6×1022 yr.
30. Limit on the proton stability independent on the decay channel.
The number of free neutrons, born in big volumes with heavy water, was proposed to use for setting
the limit on the proton decay independent on channel, and the best bound was established:
τp ≥ 4.0×1023 yr at 95% CL [2(2001)].
31. Limit on the proton decay into invisible channels.
Using the data on the number of neutrons born in the SNO solar neutrino detector with 1000 tons
of D2O (Sudbury UL, Canada), the limit on the proton decay into invisible channels was set as:
τp ≥ 3.5×1028 yr (three orders of magnitude higher than known before) [1(2003)].
32. Upper limit on the photon charge had been established from analysis of observations of extragalactic radiosources: eγ/e ≤ 3×10-33 [8(2005)]. This limit is the best to-date.
33. Development of the experimental technique and methods of simulation and analysis of experimental data.
(33.01) The ultra-low background scintillator detector with 116CdWO4 crystals and
improved passive and active shielding was created in the Solotvina UL (in particular, on the base
of big - ~200 cm3 - CdWO4 crystals) with record background rate of
0.03 counts/yr×keV×kg, that is a result of ~18 yr R&D
[2(2000), 3(2003), 4(2003)].
(33.02) New data acquisition system (16 independent channels with accumulation of the time, amplitude and shape of scintillation signal). Time-amplitude analysis of data (with possibility to discriminate the chains of decay in the natural radioactive families) [1(1995), 2(2000), 5(1996), 3(2001), 2(2003), 3(2003), 4(2003)].
(33.03) Pulse-shape analysis with discrimination of events from α and β/γ particles, double impulses, etc. [3(1998), 2(2000), 2(2003), 3(2003), 4(2003), 15(2005), 1(2007), 3(2008)].
(33.04) Event generator for description of initial kinematics of events in 2β processes and decays of radioactive nuclides (for ~3000 isotopes): how many particles and of which type were emitted, their energies, directions and times of emission [7(2000)].
(33.05) Programs for simulation (on the base of the GEANT package) of the response function of detectors for α, β and 2β decays. Programs for analysis of data with low statistics.
(33.06) Development, study of scintillation properties, pulse-shape discrimination ability and radioactive contamination of crystal scintillators [11(2005), 14(2005), 11(2006), 13(2009), 19(2010)], in particular CaWO4 [5(2005), 13(2011)], YAG:Nd [6(2005)], LaCl3:Ce [10(2005)], ZnWO4 [7(2005), 5(2008), 10(2008), 6(2009), 12(2009), 20(2010), 12(2011)], PbWO4 [1(2006), 8(2010)], CdWO4 [2(2006), 6(2016)], Li6Eu(BO3)3 [3(2007)], CaF2(Eu) [1(2007)], CaMoO4 [4(2008)], MgWO4 [10(2009)], Li2MoO4 [9(2009)], PbMoO4 [8(2010)], SrI2(Eu) [5(2012)], 7LiI(Eu) [1(2013)], BaF2 [9(2014)] as possible detectors for low counting experiments.
(33.07) Study and purification of archaeological lead for low background experiments [13(2007), 14(2011)].
(33.08) Proposal of semi-empirical calculation of quenching factors for ions in scintillators [1(2010)].
(33.09) Development and study of crystal scintillators as scintillating bolometeres: Li2MoO4 [5(2010)], 12(2013), 1(2016)], ZnMoO4 [9(2010), 2(2012), 2(2012), 10(2013), 9(2014), 4(2015), 8(2015)], 116CdWO4 [8(2016)].
(33.10) Development of crystal scintillators from enriched isotopes for double beta decay experiments: 116CdWO4 [1(1989), 10(2011)], 106CdWO4 [6(2010)], Zn100MoO4 [12(2014)].
(33.11) Rejection of random coinciding events in cryogenic double beta decay experiments [6(2012), 7(2014), 4(2017)].
(33.12) Optimization of light cllection from crystal scintillators [1(2014), 8(2014)].
(33.13) Study of luminescence in crystal scintillators [1(2017), 3(2017)].
34. Large-scale proposals in the neutrino physics and 2β research developed by the LPD group:
(1) CAMEO project for a high sensitivity study of 100Mo and 116Cd neutrinoless 2β decay [4(2000), 1(2001)]. With 100 kg of 116CdWO4 crystals placed in the liquid scintillator of the BOREXINO Counting Test Facility, working in the Gran Sasso UL, the expected T1/2 limit on 116Cd 2β0ν decay is ≈1026 yr, that corresponds to upper limit of mν ≤ 0.06 eV;
(2) in the GEM project [4(2001)] one ton of naked HP Ge detectors operating in high-purity nitrogen
is used for the search for 76Ge 2β0ν decay and dark matter investigations
(similar to the GENIUS proposal, however with simpler technical realization). Expected sensitivities are:
T1/2 ≥ 1027-1028 yr and
mν ≤ 0.015-0.05 eV;
(3) the GSO scintillators for double β searches and solar neutrino investigations are discussed in [5(1996), 3(2001)]. With 2 tons of the GSO crystals placed in the BOREXINO or SNO set-up, the sensitivity for 160Gd 2β0ν decay of T1/2 ≥ 2×1026 yr (mν ≤ 0.07 eV) could be reached;
(4) the CARVEL proposal is developed for 2β0ν decay of 48Ca
with 48CaWO4 crystal scintillators with sensitivity of
T1/2 ≥ 1027 yr and
mν ≤ 0.04-0.09 eV [2(2005)];
(5) solar neutrino detector on the base of 131Xe is proposed in [3(1997)].
Last updated 03 January 2017