Recent results from KamLAND-Zen

We discuss up-to-date constraints on the Majorana neutrino mass $m_{\beta\beta}$ from neutrinoless double beta decay ($0\nu\beta\beta$) searches in experiments using different isotopes: KamLAND-Zen and EXO ($^{136}$Xe), GERDA and MAJORANA ($^{76}$Ge) and CUORE ($^{130}$Te). Best fits and upper bounds on $m_{\beta\beta}$ are explored in the general landscape of nuclear matrix elements (NME), as well as for specific NME values obtained in representative nuclear models. By approximating the likelihood of $0\nu\beta\beta$ signals through quadratic forms, the analysis of separate and combined isotope data becomes exceedingly simple, and allows to clarify various aspects of multi-isotope data combinations. In particular, we analyze the relative impact of different data in setting upper bounds on $m_{\beta\beta}$, as well as the conditions leading to nonzero $m_{\beta\beta}$ at best fit, for variable values of the NMEs. Detailed results on $m_{\beta\beta}$ from various combinations of data are reported in graphical and numerical form. Implications for future $0\nu\beta\beta$ data analyses and NME calculations are briefly discussed.

We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg·yr, or equivalently 22.2 kg·yr of 136Xe exposure. At the region around 136Xe decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.1 yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass eV. This is the first NLDBD result reported from a dual-phase xenon experiment.

Evaluation of the spin wave green's functions for rutile structure Heisenberg antiferromagnets with exchange between ions both on the same and opposite sublattices

Cuoricino was a cryogenic bolometric detector operating in Gran Sasso Underground Laboratory, Italy, from March 2003 to June 2008. With its 40.7 kg of 130TeO2 in the form of an array of 62 crystals it has set the currently best lower limit on the halflife of 130Te neutrinoless double beta decay, T1/2 > 2.94 · 1024 y at 90 % CL. It has moreover proven the feasibility of the CUORE experiment, whose aim is to be sensitive to values of the effective neutrino mass as low as few tens of meV. We will report on the latest results from Cuoricino and on the status of the CUORE project.

The Q value of the double-beta (β-β-) decay of 104Ru (Qβ-β--value) was determined using the JYFLTRAP double Penning trap mass spectrometer employing the Phase-Imaging Ion Cyclotron Resonance (PI-ICR) method. The obtained value of 1297.705(36) keV is in agreement with the current literature value of 1299.4(27) keV but is over 70 times more precise. As a consistency check on a 100 eV level, we also measured the precisely known 102Pd double-electron capture Q value, QECEC=1203.531(92) keV, which agrees with the literature value of 1203.47(4) keV. The measured Q value of 104Ru β-β- decay was used in calculations of the phase-space factors of the double-beta decay. Also, the nuclear matrix elements were calculated using the microscopic interacting boson model (IBM-2) as a nuclear model and compared with other available results. With these theoretical calculations based on the measured Q value, the estimates for the two-neutrino and neutrinoless double-beta decay half-lives of 104Ru were calculated to be t1/22νββ>5.449×10215.449\ imes 10^{21}$$\\end{document}]]> years and t1/20νββ>5.775×10265.775\ imes 10^{26}$$\\end{document}]]> years, respectively. The calculated 2νβ-β- half-life is longer than the current experimental lower limit but short enough to be potentially within reach with future high precision experiments.

If it hasn’t failed, does it work? On ‘the worst we can expect’ from observational trial results, with reference to airway management devices

Neutrinoless double-beta (0νββ) decay is a heretofore unobserved process which, if observed, would imply that neutrinos are Majorana particles. Interpretations of the stringent experimental constraints on 0νββ-decay half-lives require calculations of nuclear matrix elements. This work presents the first lattice quantum chromodynamics (LQCD) calculation of the matrix element for 0νββ decay in a multinucleon system, specifically the nn→ppee transition, mediated by a light left-handed Majorana neutrino propagating over nuclear-scale distances. This calculation is performed with quark masses corresponding to a pion mass of mπ=806 MeV at a single lattice spacing and volume. The statistically cleaner Σ−→Σ+ee transition is also computed in order to investigate various systematic uncertainties. The prospects for matching the results of LQCD calculations onto a nuclear effective field theory to determine a leading-order low-energy constant relevant for 0νββ decay with a light Majorana neutrino are investigated. This work, therefore, sets the stage for future calculations at physical values of the quark masses that, combined with effective field theory and nuclear many-body studies, will provide controlled theoretical inputs to experimental searches of 0νββ decay. Published by the American Physical Society 2024

The NEMO 3 experiment searches for neutrinoless double beta decay and makes precision measurements of two-neutrino double beta decay in seven isotopes. The latest two-neutrino half-life results are presented, together with the limits on neutrinoless half-lives and the corresponding effective Majorana neutrino masses. Also given are the limits obtained on neutrinoless double beta decay mediated by Rp-violating SUSY, right-hand currents and different Majoron emission modes.

The neutrinoless double beta decay transition to the first excited 0^+ collective final state is examined for A=76, 82, 100 and 136 nuclei by assuming light and heavy Majorana neutrino exchange mechanisms as well as the trilinear R-parity violating contributions. Realistic calculations of nuclear matrix elements have been performed within the renormalized quasiparticle random phase approximation. Transitions to the first excited two-quadrupole phonon 0^+ state are described within a boson expansion formalism and alternatively by using the operator recoupling method. We present the sensitivity parameters to different lepton number violating signals, which can be used in planning the neutrinoless double beta decay experiments. The half-life of neutrinoless double beta decay to the first excited state 0^+_1 is by a factor of 10 to 100 larger than that of the transition to the ground state.

Cryogenic Double Beta Decay Experiments: CUORE and CUORICINO

We present an improved search for neutrinoless double-beta (0νββ) decay of ^{136}Xe in the KamLAND-Zen experiment. Owing to purification of the xenon-loaded liquid scintillator, we achieved a significant reduction of the ^{110m}Ag contaminant identified in previous searches. Combining the results from the first and second phase, we obtain a lower limit for the 0νββ decay half-life of T_{1/2}^{0ν}>1.07×10^{26} yr at 90%C.L., an almost sixfold improvement over previous limits. Using commonly adopted nuclear matrix element calculations, the corresponding upper limits on the effective Majorana neutrino mass are in the range 61-165meV. For the most optimistic nuclear matrix elements, this limit reaches the bottom of the quasidegenerate neutrino mass region.

The Enriched Xenon Observatory (EXO) is an experimental program which aims to observe the neutrinoless double beta decay of Xe-136. The existence of this process requires neutrinos to be Majorana particles and in its simplest interpretation the rate of decay provides a measurement of the absolute neutrino mass. The first stage of the experiment, EXO-200, features 200 kg of liquid xenon, enriched to 80% in Xe-136. The detector, located at the Waste Isolation Pilot Plant in New Mexico, has been in operation for about one and a half years, and the two-neutrino double beta decay of Xe-136 has been measured. Its half life of T1/22νββ = 2.23±0.017(stat)±0.22(sys)×1021 yr makes it the slowest process ever measured directly. No evidence for neutrinoless decay has been found with an exposure of 32.5 kg-yr. A lower limit for the half life has been set to T1/20νββ(136Xe)>1.6×1025 yr (90% CL), corresponding to effective Majorana masses of less than 140-380 meV, depending on the matrix element calculation.

Neutrinoless double beta (0νββ) decay searches are currently among the major foci of experimental physics. The observation of such a decay will have important implications in our understanding of the intrinsic nature of neutrinos and shed light on the limitations of the Standard Model. The rate of this process depends on both the unknown neutrino effective mass and the nuclear matrix element (M0ν) associated with the given 0νββ transition. The latter can only be provided by theoretical calculations, hence the need of accurate theoretical predictions of M0ν for the success of the experimental programs. This need drives the theoretical nuclear physics community to provide the most reliable calculations of M0ν. Among the various computational models adopted to solve the many-body nuclear problem, the shell model is widely considered as the basic framework of the microscopic description of the nucleus. Here, we review the most recent and advanced shell-model calculations of M0ν considering the light-neutrino-exchange channel for nuclei of experimental interest. We report the sensitivity of the theoretical calculations with respect to variations in the model spaces and the shell-model nuclear Hamiltonians.

The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated the large potential of double beta decay to search for new physics beyond the Standard Model. To increase by a major step the present sensitivity for double beta decay and dark matter search much bigger source strengths and much lower backgrounds are needed than used in experiments under operation at present or under construction. We present here a study of a project proposed recently [1], which would operate one ton of ‘naked’ enriched GErmanium-detectorsinliquid NItrogenas shielding in an Underground Setup (GENIUS). It improves the sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe neutrino masses even down to 10−3 eV. The first version would allow to test the atmospheric neutrino problem, the second at least part of the solar neutrino problem. Both versions would allow in addition significant contributions to testing several classes of GUT models. These are especially tests of R-parity breaking supersymmetry models, leptoquark masses and mechanism and right-handed W-boson masses comparable to LHC. The second issue of the experiment is the search for dark matter in the universe. The entire MSSM parameter space for prediction of neutralinos as dark matter particles could be covered already in a first step of the full experiment with the same purity requirements, but using only 100 kg of 76Ge or even of natural Ge making the experiment competitive to LHC in the search for supersymmetry. The layout ofthe proposed experiment is discussed and the shielding and purity requirements are studied using GEANT Monte Carlo simulations. As a demonstration of the feasibility of the experiment first results of operating a ‘naked’ Ge detector in liquid nitrogen are presented.

A search for double beta decay of 116Cd and 196Hg was made in the Solotvina underground laboratory operating at 1000 m w.e.