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Register a new userSearch for neutrinoless quadruple-$beta$ decay of $^{150}$Nd with the NEMO-3 detector
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We report the results of a first experimental search for lepton number violation by four units in the neutrinoless quadruple-$beta$ decay of $^{150}$Nd using a total exposure of $0.19$ kg$cdot$y recorded with the NEMO-3 detector at the Modane Underground Laboratory (LSM). We find no evidence of this decay and set lower limits on the half-life in the range $T_{1/2}>(1.1-3.2)times10^{21}$ y at the $90%$ CL, depending on the model used for the kinematic distributions of the emitted electrons.
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We report the results of a search for the neutrinoless double-$beta$ decay (0$ ubetabeta$) 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$ ubetabeta$ signal has been found, yielding a limit for the light Majorana neutrino mass mechanism of $T_{1/2}(0 ubetabeta)>1.1 times 10^{24}$ 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 $< m_{ u} > < 0.3-0.9$ eV (90% C.L.). Constraints on other lepton number violating mechanisms of 0$ ubetabeta$ 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 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 $T^{2 u}_{1/2},=,[6.4, ^{+0.7}_{-0.6}{rm (stat.)} , ^{+1.2}_{-0.9}{rm (syst.)}] times 10^{19},{rm yr}$. 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 $T^{0 u}_{1/2} > 2.0 times 10^{22},{rm yr}$ at $90%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $< m_{betabeta} > < 6.0 - 26$ ${rm eV}$, 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 $beta$ ($0 ubetabeta$) decay. We report final results of a search for $0 ubetabeta$ 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 $0 ubetabeta$ signal region and find no evidence of $0 ubetabeta$ decays in the data. The level of observed background in the $0 ubetabeta$ 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 $0 ubetabeta$ decays in $^{100}$Mo of $T_{1/2}(0 ubetabeta)> 1.1 times 10^{24}$ 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 $langle m_{ u} rangle < 0.33$--$0.62$ eV. We also report constraints on other lepton-number violating mechanisms for $0 ubetabeta$ decays.
We present results from a search for neutrinoless double-$beta$ ($0 ubetabeta$) decay using 36.6 g of the isotope $^{150}$Nd with data corresponding to a live time of 5.25 y recorded with the NEMO-3 detector. We construct a complete background model for this isotope, including a measurement of the two-neutrino double-$beta$ decay half-life of $T^{2 u}_{1/2}=$[9.34 $pm$ 0.22 (stat.) $^{+0.62}_{-0.60}$ (syst.)]$times 10^{18}$ y for the ground state transition, which represents the most precise result to date for this isotope. We perform a multivariate analysis to search for zeronu decays in order to improve the sensitivity and, in the case of observation, disentangle the possible underlying decay mechanisms. As no evidence for zeronu decay is observed, we derive lower limits on half-lives for several mechanisms involving physics beyond the Standard Model. The observed lower limit, assuming light Majorana neutrino exchange mediates the decay, is $T^{0 u}_{1/2} >$ 2.0 $times 10^{22}$ y at the 90% C.L., corresponding to an upper limit on the effective neutrino mass of $langle m_{ u} rangle$ $<$ 1.6 - 5.3 eV..
Results from a search for neutrinoless double-beta decay $0 ubetabeta$ of $^{136}$Xe are presented using the first year of data taken with the upgraded EXO-200 detector. Relative to previous searches by EXO-200, the energy resolution of the detector has been improved to $sigma/E$=1.23%, the electric field in the drift region has been raised by 50%, and a system to suppress radon in the volume between the cryostat and lead shielding has been implemented. In addition, analysis techniques that improve topological discrimination between $0 ubetabeta$ and background events have been developed. Incorporating these hardware and analysis improvements, the median 90% confidence level $0 ubetabeta$ half-life sensitivity after combining with the full data set acquired before the upgrade has increased 2-fold to $3.7 times 10^{25}$ yr. No statistically significant evidence for $0 ubetabeta$ is observed, leading to a lower limit on the $0 ubetabeta$ half-life of $1.8times10^{25}$ yr at the 90% confidence level.
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