Session G16: Neutrinoless Double Beta Decay and Neutrino Mass

First results from the CUORE \boldmath$0\nu\beta\beta$ decay experiment

CUORE---the Cryogenic Underground Observatory for Rare Events---is an experiment searching for the $0\nu\beta\beta$ decay of $^{130}$Te, located at the Laboratori Nazionali del Gran Sasso in Italy. The detector comprises 988 $5 \times 5 \times 5$ cm$^3$ TeO$_2$ crystals operated as bolometers at $\sim$10 mK in the world's largest and most powerful dilution refrigerator. CUORE began physics data collection in spring 2017, and has recently published a lower limit of $T_{1/2}^{0\nu} (^{130}Te) > 1.3 \times 10^{25}$ y (90\% C.L.) on the decay half-life---the most sensitive to date for this isotope. We present the analysis leading to this result, including a discussion of spectral line shape modeling and fitting.   

Status and results of the EXO-200 experiment.

The EXO-200 experiment searches for the neutrinoless double-beta decay of Xe136 with an ultra low-background time projection chamber filled with approximately 170 kg enriched Xe. Observation of this rare decay mode would signify the Majorana nature of neutrinos and new physics beyond the Standard Model. The EXO-200 detector was successfully upgraded with new front-end electronics and a radon suppression system and started its Phase-II operation in April 2016. In this talk, we will present recent results and current status of the experiment.   

Search for nucleon decays with EXO-200

A search for instability of nucleons bound in $^{136}$Xe nuclei is reported with 223 kg$\cdot$yr exposure of $^{136}$Xe in the EXO-200 experiment. Lower lifetime limits of 3.3$\times 10^{23}$ and 1.9$\times 10^{23}$~yrs are established for nucleon decay to $^{133}$Sb and $^{133}$Te, respectively. These are the most stringent to date, exceeding the prior decay limits by a factor of 9 and 7, respectively.   

Results and Status of the {\sc Majorana Demonstrator}

Neutrinoless double-beta decay ($0\nu\beta\beta$) is a hypothetical lepton-number violating process that would indicate that neutrinos are Majorana fermions. The {\sc Majorana Demonstrator} is searching for $0\nu\beta\beta$ in $^{76}$Ge using a modular array of high purity Germanium (HPGe) detectors with support and shielding constructed out of low-background materials and housed at the '4850 level of the Sanford Underground Research Facility. The experiment contains two modules, totaling 44.8~kg of p-type point contact HPGe detectors, 29.7~kg of which are enriched in $^{76}$Ge. Both modules have been in operation since August 2016, and with 10~kg~yr of unblinded exposure have achieved a limit of $>1.9\times10^{25}$~yr on the decay half life. The {\sc Demonstrator} has achieved an excellent energy resolution of 0.1\% FWHM at the 2039~keV ROI, and has among the lowest ROI backgrounds of current generation $0\nu\beta\beta$ searches. This talk will contain an overview of this result and the current status of the experiment. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics and Nuclear Physics Programs of the National Science Foundation, and the Sanford Underground Research Facility.   

The Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND)

The seesaw model can explain the small but finite neutrino masses and requires neutrinos to be Majorana particles, \textit{i.e.} fermions that are their own antiparticles. Neutrinoless double beta decay (NLDBD) is a hypothetical lepton-number-violating process that is possible only if neutrinos are Majorana particles. The discovery of NLDBD would unambiguously establish the Majorana nature of neutrinos and explicitly demonstrate that the total lepton number is violated. \textsc{Majorana} \textsc{Demonstrator} and GERDA, the two current generation experiments searching for NLDBD in $^{76}$Ge, have achieved comparable low backgrounds and excellent energy resolutions with very distinct configurations. The Large Enriched Germanium Experiment for~Neutrinoless Double Beta Decay (LEGEND) collaboration has been formed to pursue a tonne-scale $^{76}$Ge experiment integrating the best technologies of these two experiments. The collaboration aims to develop a phased, $^{76}$Ge based double-beta decay experimental program with discovery potential at a half-life beyond $10^{28}$ years, using existing resources as appropriate to expedite physics results. In this talk, I will discuss the goals, strategies and R$\&$D efforts of the LEGEND project.   

SNO+: Into the second phase

The multi-phase SNO+ experiment has been operating with a water target for nearly 1 year. The forthcoming results of this first phase include a search for nucleon decay, characterization of detector-related backgrounds, and a complete detector calibration with a number of deployed and embedded sources. In addition, SNO+ is preparing to fill the detector with liquid scintillator in Spring 2018. The scope of this second phase includes measuring solar neutrinos, reactor neutrinos, and geoneutrinos, and characterizing scintillator-related backgrounds. After several months, the third phase is planned to begin a high-sensitivity search for neutrinoless double beta decay using $^{130}$Te-loaded scintillator. This talk presents the current status and prospective measurements of the SNO+ experiment.   

Towards an improved neutrino mass measurement: a KATRIN status report

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to make a precision mass measurement of the neutrino by leveraging the kinematics of tritium beta decay, to a design mass sensitivity of 0.2eV (90\% C.L.). Currently in the late commissioning stages, KATRIN has seen first transmission of electrons through its complete 70m beamline, characterized backgrounds and subsystems via extensive analysis of commissioning data, and run calibration tests with multiple krypton sources. A summary of results will be given here, as well as an outlook to both the immediate and extended future.   

ABRACADABRA: A Broadband and Resonant Search for Axion Dark Matter

ABRACADABRA is a proposed experiment to search for ultralight ($10^{-14} - 10^{-6}$ eV) axion dark matter. When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. In the presence of axion dark matter, a toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. The readout circuit can be broadband or resonant. In this talk I will review the design and sensitivity of the experiment. I will also show preliminary results from a 10-cm prototype and present a program to probe the QCD axion at the GUT scale.