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Register a new userFirst Search for Lorentz and CPT Violation in Double Beta Decay with EXO-200
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A search for Lorentz- and CPT-violating signals in the double beta decay spectrum of $^{136}$Xe has been performed using an exposure of 100 kg$cdot$yr with the EXO-200 detector. No significant evidence of the spectral modification due to isotropic Lorentz-violation was found, and a two-sided limit of $-2.65 times 10^{-5 } ; textrm{GeV} < mathring{a}^{(3)}_{text{of}} < 7.60 times 10^{-6} ; textrm{GeV}$ (90% C.L.) is placed on the relevant coefficient within the Standard-Model Extension (SME). This is the first experimental study of the effect of the SME-defined oscillation-free and momentum-independent neutrino coupling operator on the double beta decay process.
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We present the search for Lorentz violation in the double beta decay of ^{82}Se~with CUPID-0, using an exposure of 9.95 kg x y. We found no evidence for the searched signal and set a limit on the isotropic components of the Lorentz violating coefficient of $mathring{a}_{text{of}}^{(3)} < 4.1cdot10^{-6}$ GeV (90% Credible Interval). This results is obtained with a Bayesian analysis of the experimental data and fully includes the systematic uncertainties of the model. This is the first limit on $mathring{a}_{text{of}}^{(3)}$ obtained with a scintillating bolometer, showing the potentiality of this technique.
We report on a search for neutrinoless double-beta decay of $^{136}$Xe with EXO-200. No signal is observed for an exposure of 32.5 kg-yr, with a background of ~1.5 x 10^{-3} /(kg yr keV) in the $pm 1sigma$ region of interest. This sets a lower limit on the half-life of the neutrinoless double-beta decay $T_{1/2}^{0 ubetabeta}$($^{136}$Xe) > 1.6 x 10$^{25}$ yr (90% CL), corresponding to effective Majorana masses of less than 140-380 meV, depending on the matrix element calculation.
A search for neutrinoless double-beta decay ($0 ubetabeta$) in $^{136}$Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between $0 ubetabeta$ and background events. Relative to previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4$pm$3.0% and the energy resolution of the detector at the Q-value of $^{136}$Xe $0 ubetabeta$ has been improved from $sigma/E=1.23%$ to $1.15pm0.02%$ with the upgraded detector. Accounting for the new data, the median 90% confidence level $0 ubetabeta$ half-life sensitivity for this analysis is $5.0 cdot 10^{25}$ yr with a total $^{136}$Xe exposure of 234.1 kg$cdot$yr. No statistically significant evidence for $0 ubetabeta$ is observed, leading to a lower limit on the $0 ubetabeta$ half-life of $3.5cdot10^{25}$ yr at the 90% confidence level.
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.
We report the observation of two-neutrino double-beta decay in Xe-136 with T_1/2 = 2.11 +- 0.04 (stat.) +- 0.21 (sys.) x 10^21 yr. This second order process, predicted by the Standard Model, has been observed for several nuclei but not for Xe-136. The observed decay rate provides new input to matrix element calculations and to the search for the more interesting neutrino-less double-beta decay, the most sensitive probe for the existence of Majorana particles and the measurement of the neutrino mass scale.
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