Search

We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-β decay of Nd150 using a total exposure of 0.19 kg yr recorded with the NEMO-3 detector at the Modane Underground Laboratory. We find no evidence of this decay and set lower limits on the half-life in the range T1/2>(1.1–3.2)×1021 yr at the 90% C.L., depending on the model used for the kinematic distributions of the emitted electrons.

The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-$\beta$ decay of $^{48}{\rm Ca}$. Using $5.25$ yr of data recorded with a $6.99\,{\rm g}$ sample of $^{48}{\rm Ca}$, approximately $150$ double-$\beta$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-$\beta$ decay of $^{48}{\rm Ca}$ has been measured to be $T^{2\nu}_{1/2}\,=\,[6.4\, ^{+0.7}_{-0.6}{\rm (stat.)} \, ^{+1.2}_{-0.9}{\rm (syst.)}] \times 10^{19}\,{\rm yr}$. A search for neutrinoless double-$\beta$ decay of $^{48}{\rm Ca}$ yields a null result and a corresponding lower limit on the half-life is found to be $T^{0\nu}_{1/2} > 2.0 \times 10^{22}\,{\rm yr}$ at $90\%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $ < 6.0 - 26$ ${\rm eV}$, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.

The NEMO-3 detector, which had been operating in the Modane Underground Laboratory from 2003 to 2010, was designed to search for neutrinoless double $\beta$ ($0\nu\beta\beta$) decay. We report final results of a search for $0\nu\beta\beta$ decays with $6.914$ kg of $^{100}$Mo using the entire NEMO-3 data set with a detector live time of $4.96$ yr, which corresponds to an exposure of 34.3 kg$\cdot$yr. We perform a detailed study of the expected background in the $0\nu\beta\beta$ signal region and find no evidence of $0\nu\beta\beta$ decays in the data. The level of observed background in the $0\nu\beta\beta$ signal region $[2.8-3.2]$ MeV is $0.44 \pm 0.13$ counts/yr/kg, and no events are observed in the interval $[3.2-10]$ MeV. We therefore derive a lower limit on the half-life of $0\nu\beta\beta$ decays in $^{100}$Mo of $T_{1/2}(0\nu\beta\beta)> 1.1 \times 10^{24}$ yr at the $90\%$ Confidence Level, under the hypothesis of light Majorana neutrino exchange. Depending on the model used for calculating nuclear matrix elements, the limit for the effective Majorana neutrino mass lies in the range $\langle m_{\nu} \rangle < 0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0\nu\beta\beta$ decays.

We report the results of a search for the neutrinoless double-$\beta$ decay (0$\nu\beta\beta$) of $^{100}$Mo, using the NEMO-3 detector to reconstruct the full topology of the final state events. With an exposure of 34.7 kg.y, no evidence for the 0$\nu\beta\beta$ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of $T_{1/2}(0\nu\beta\beta)>1.1 \times 10^{24}$ years (90% C.L.) once both statistical and systematic uncertainties are taken into account. Depending on the Nuclear Matrix Elements this corresponds to an upper limit on the Majorana effective neutrino mass of $ < 0.3-0.8$ eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0$\nu\beta\beta$ decays are also given. Searching for high-energy double electron events in all suitable sources of the detector, no event in the energy region [3.2-10] MeV is observed for an exposure of 47 kg.y.

The half-life for double-{beta} decay of {sup 150}Nd has been measured by the NEMO-3 experiment at the Modane Underground Laboratory. Using 924.7 days of data recorded with 36.55 g of {sup 150}Nd, we measured the half-life for 2{nu}{beta}{beta} decay to be T{sub 1/2}{sup 2{nu}}=(9.11{sub -0.22}{sup +0.25}(stat.){+-}0.63(syst.))x10{sup 18} yr. The observed limit on the half-life for neutrinoless double-{beta} decay is found to be T{sub 1/2}{sup 0{nu}}>1.8x10{sup 22} yr at 90% confidence level. This translates into a limit on the effective Majorana neutrino mass of

Final results of the double $\ensuremath{\beta}$ decay experiment, performed with the help of low background ${}^{116}{\mathrm{CdWO}}_{4}$ crystal scintillators in the Solotvina Underground Laboratory, are presented. In particular, the revised half-life value of the two-neutrino 2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ has been measured as ${T}_{1/2}^{2\ensuremath{\nu}}{=2.9}_{\ensuremath{-}0.3}^{+0.4}\ifmmode\times\else\texttimes\fi{}{10}^{19}\mathrm{yr},$ and the new half-life limit on the neutrinoless $2\ensuremath{\beta}$ decay of ${}^{116}\mathrm{Cd}$ has been established as ${T}_{1/2}^{0\ensuremath{\nu}}g~1.7(2.6)\ifmmode\times\else\texttimes\fi{}{10}^{23}\mathrm{yr}$ at 90% (68%) C.L. The latter corresponds to a restriction on the neutrino mass: ${m}_{\ensuremath{\nu}}l~1.7(1.4)\mathrm{eV}$ at 90% (68%) C.L. Besides, new ${T}_{1/2}$ bounds (at the level of ${10}^{17}\char21{}{10}^{21}\mathrm{yr})$ were set for various $2\ensuremath{\beta}$ processes in ${}^{106}\mathrm{Cd},$ ${}^{108}\mathrm{Cd},$ ${}^{114}\mathrm{Cd},$ ${}^{180}\mathrm{W},$ and ${}^{186}\mathrm{W}$ nuclei.

A new phase of a ${}^{116}\mathrm{Cd}$ double \ensuremath{\beta} decay experiment is in progress in the Solotvina Underground Laboratory. Four enriched ${}^{116}{\mathrm{CdWO}}_{4}$ scintillators with total mass of 339 g are used in a setup, whose active shield is made of 15 natural ${\mathrm{CdWO}}_{4}$ crystals (20.6 kg). The background rate in the energy interval 2.5--3.2 MeV is 0.03 counts/yr kg keV. The half-life for 2\ensuremath{\nu}2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ is measured as ${T}_{1/2}(2\ensuremath{\nu})=2.6\ifmmode\pm\else\textpm\fi{}0.1(\mathrm{stat}{)}_{\ensuremath{-}0.4}^{+0.7}(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{19}$ yr. The ${T}_{1/2}$ limits for neutrinoless 2\ensuremath{\beta} decay of ${}^{116}\mathrm{Cd}$ are set at ${T}_{1/2}g~0.7(2.5)\ifmmode\times\else\texttimes\fi{}{10}^{23}$ yr at 90%(68%) C.L. for transition to ground state of ${}^{116}\mathrm{Sn},$ while for decays to the first ${2}_{1}^{+}$ and second ${0}_{1}^{+}$ excited levels of ${}^{116}\mathrm{Sn}$ at ${T}_{1/2}g~1.3(4.8)\ifmmode\times\else\texttimes\fi{}{10}^{22}$ yr and $g~0.7(2.4)\ifmmode\times\else\texttimes\fi{}{10}^{22}$ yr with 90%(68%) C.L., respectively. For 0\ensuremath{\nu}2\ensuremath{\beta} decay with emission of one or two Majorons, the limits are ${T}_{1/2}(0\ensuremath{\nu}M1)g~3.7(5.8)\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr and ${T}_{1/2}(0\ensuremath{\nu}M2)g~5.9(9.4)\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr 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 ${m}_{\ensuremath{\nu}}l~2.6(1.4)$ eV, $\ensuremath{\eta}l~3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8},$ $\ensuremath{\lambda}l~3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6},$ and ${g}_{M}l~12(9.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ at 90%(68%) C.L., respectively.

A new lifetime limit on the charge nonconserving (CNC) electron decay through the channel e(-)-->nu(e)gamma has been established analyzing a 2257.7 kg day event sample collected by the similar or equal to 6.5 kg liquid xenon DAMA scintillator at the Gran Sasso National Laboratory of INFN. This limit is tau>2.0(3.4)x10(26) yr at 90% (68%) C.L., one order of magnitude higher than the current limit for that channel.