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1. Search for Periodic Modulations of the Rate of Double-Beta Decay of 100Mo in the NEMO-3 Detector

   R. Arnold, 1 C. (November 2020, ArXivorg)

   Double-beta decays of 100Mo from the 6.0195-year exposure of a 6.914 kg high-purity sample were recorded by the NEMO-3 experiment that searched for neutrinoless double-beta decays. These ultra-rare transitions to 100Ru have a half-life of approximately 7  1018 years, and have been used to conduct the rst ever search for periodic variations of this decay mode. The Lomb-Scargle periodogram technique, and its error-weighted extension, were employed to look for periodic modulations of the half-life. Monte Carlo modeling was used to study the modulation sensitivity of the data over a broad range of amplitudes and frequencies. Data show no evidence of modulations with amplitude greater than 2.5% in the frequency range of 0:33225 y􀀀1 to 365:25 y􀀀1. 

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2. Search for double-beta decay of $$\mathrm {^{130}Te}$$ to the $$0^+$$ states of $$\mathrm {^{130}Xe}$$ with CUORE

   https://doi.org/10.1140/epjc/s10052-021-09317-z  

   Adams, D. Q.; Alduino, C.; Alfonso, K.; Avignone, F. T.; Azzolini, O.; Bari, G.; Bellini, F.; Benato, G.; Biassoni, M.; Branca, A.; et al (July 2021, The European Physical Journal C)

   null (Ed.)

   Abstract The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) in the isotope $$\mathrm {^{130}Te}$$ 130 Te . In this work we present the latest results on two searches for the double beta decay (DBD) of $$\mathrm {^{130}Te}$$ 130 Te to the first $$0^{+}_2$$ 0 2 + excited state of $$\mathrm {^{130}Xe}$$ 130 Xe : the $$0\nu \beta \beta $$ 0 ν β β decay and the Standard Model-allowed two-neutrinos double beta decay ( $$2\nu \beta \beta $$ 2 ν β β ). Both searches are based on a 372.5 kg $$\times $$ × yr TeO $$_2$$ 2 exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as $$\mathrm {S^{0\nu }_{1/2} = 5.6 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 0 ν = 5.6 × 10 24 yr for the $${0\nu \beta \beta }$$ 0 ν β β decay and $$\mathrm {S^{2\nu }_{1/2} = 2.1 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 2 ν = 2.1 × 10 24 yr for the $${2\nu \beta \beta }$$ 2 ν β β decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at $$90\%$$ 90 % C.I. on the decay half lives is obtained as: $$\mathrm {(T_{1/2})^{0\nu }_{0^+_2} > 5.9 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 0 ν > 5.9 × 10 24 yr for the $$0\nu \beta \beta $$ 0 ν β β mode and $$\mathrm {(T_{1/2})^{2\nu }_{0^+_2} > 1.3 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 2 ν > 1.3 × 10 24 yr for the $$2\nu \beta \beta $$ 2 ν β β mode. These represent the most stringent limits on the DBD of $$^{130}$$ 130 Te to excited states and improve by a factor $$\sim 5$$ ∼ 5 the previous results on this process. 

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3. Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO

   https://doi.org/10.1140/epjc/s10052-022-11072-8  

   Gallina, G.; Guan, Y.; Retiere, F.; Cao, G.; Bolotnikov, A.; Kotov, I.; Rescia, S.; Soma, A. K.; Tsang, T.; Darroch, L.; et al (December 2022, The European Physical Journal C)

   Abstract Liquid xenon time projection chambers are promising detectors to search for neutrinoless double beta decay (0 $$\nu \beta \beta $$ ν β β ), due to their response uniformity, monolithic sensitive volume, scalability to large target masses, and suitability for extremely low background operations. The nEXO collaboration has designed a tonne-scale time projection chamber that aims to search for 0 $$\nu \beta \beta $$ ν β β of $$^{136}$$ 136 Xe with projected half-life sensitivity of $$1.35\times 10^{28}$$ 1.35 × 10 28  yr. To reach this sensitivity, the design goal for nEXO is $$\le $$ ≤ 1% energy resolution at the decay Q -value ( $$2458.07\pm 0.31$$ 2458.07 ± 0.31  keV). Reaching this resolution requires the efficient collection of both the ionization and scintillation produced in the detector. The nEXO design employs Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm scintillation light of liquid xenon. This paper reports on the characterization of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3 SiPMs specifically designed for nEXO, as well as new measurements on new test samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters (MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct crosstalk, correlated avalanches and photon detection efficiency were measured as a function of the applied over voltage and wavelength at liquid xenon temperature (163 K). The results from this study are used to provide updated estimates of the achievable energy resolution at the decay Q -value for the nEXO design. 

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4. Observation of two-neutrino double electron capture in 124Xe with XENON1T

   https://doi.org/10.1038/s41586-019-1124-4  

   E. Aprile, 1J. Aalbers (April 2019, Nature)

   Two-neutrino double electron capture (2νECEC) is a second-order Weak process with predictedhalf-lives that surpass the age of the Universe by many orders of magnitude [1]. Until now, indi-cations for 2νECEC decays have only been seen for two isotopes,78Kr [2, 3] and130Ba [4, 5], andinstruments with very low background levels are needed to detect them directly with high statisticalsignificance [6, 7]. The 2νECEC half-life provides an important input for nuclear structure models[8–14] and its measurement represents a first step in the search for the neutrinoless double electroncapture processes (0νECEC). A detection of the latter would have implications for the nature of theneutrino and give access to the absolute neutrino mass [15–17]. Here we report on the first directobservation of 2νECEC in124Xe with the XENON1T Dark Matter detector. The significance of thesignal is 4.4σand the corresponding half-lifeT2νECEC1/2= (1.8±0.5stat±0.1sys)×1022y is the longestever measured directly. This study demonstrates that the low background and large target massof xenon-based Dark Matter detectors make them well suited to measuring other rare processes aswell, and it highlights the broad physics reach for even larger next-generation experiments 

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5. Neutrinoless double β decay with light sterile neutrinos: the contact terms

   https://doi.org/10.1007/JHEP04(2025)181  

   Cirigliano, Vincenzo; Dekens, Wouter; Quiroga, Sebastián Urrutia (April 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> We study neutrinoless double-beta decay in extensions of the Standard Model that includenright-handed neutrino singlets, with massesm_sbelow the GeV scale. Generalizing recently developed matching methods, we determine them_sdependence of the short-rangenn→ppcouplings that appear to leading order in the chiral effective field theory description of neutrinoless double beta decay. We focus on two scenarios, corresponding to the minimalνSM and left-right symmetric models. We illustrate the impact of our new results in the case of theνSM, showing a significant impact on the neutrinoless double-beta decay half-life whenm_sis in the 200–800 MeV range. 

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