Session Q14: Mini-Symposium: Neutrino Properties: New Developments, Challenges and Impacts

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Exploration of Germanium (Ge) detectors with amorphous Ge (a-Ge) contacts has drawn attention to the searches for rare-event physics such as dark matter and neutrinoless double-beta decay. The charge barrier height (CBH) of the a-Ge contacts deposited on the detector surface is crucial to suppress the leakage current of the detector in order to achieve a low-energy detection threshold and high-energy resolution. The temperature-dependent CBH of a-Ge contacts for three Ge detectors is analyzed to study the bulk leakage current (BLC) characteristics. The results show that CBH is temperature dependent. The direct relation of the CBH variation to temperature is related to the barrier inhomogeneities created on the interface of a-Ge and crystalline Ge. The inhomogeneities that occur at the interface were analyzed using the Gaussian distribution model for three detectors. The implication of the CBH at zero temperature is discussed for Ge detectors with a-Ge contacts in searching for rare-event physics.   

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Project 8 is a neutrino mass experiment with the tritium endpoint method, with the projected sensitivity on neutrino mass at ~40meV. To achieve this sensitivity, the Project 8 Collaboration has developed a novel technique called Cyclotron Radiation Emission Spectroscopy (CRES). Taking a phased approach in four phases, we have measured the first tritium spectrum with CRES in Phase II of Project 8. In this talk I will give an overview of Phase II and the analysis, showing Phase II results have positioned us well going forward into future phases.   

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The Project 8 collaboration endeavors to measure the electron-weighted neutrino mass to within 40 meV using Cyclotron Radiation Emission Spectroscopy (CRES). The upcoming Phase III of Project 8 will provide the first demonstration of CRES in free space. Electrons near the endpoint of tritium beta decay with energy 18.6 keV will be trapped magnetically and surrounded by an array of antennas detecting their cyclotron radiation. A numerical simulation approach has been developed to compute the response of the antenna array to radiation from the trapped electrons. Motivation for the approach and its implications for the experiment design will be discussed.   

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Project 8 is designed to directly measure the electron-weighted neutrino mass using cyclotron radiation emission spectroscopy~(CRES). Using the cyclotron frequency as a proxy for kinetic energy, the experiment aims to measure the tritium beta-decay electron endpoint spectrum of electrons trapped in a 1T magnetic field to reach a mass sensitivity of 40 meV/c$^2$. Following the successful demonstration of CRES with waveguides, the upcoming Phase III of Project 8 will demonstrate CRES in free space by utilizing a larger volume instrumented with antennas. This talk will give an overview of the detector design and describe the development of event reconstruction techniques for observing cyclotron radiation in the Project 8 free space CRES demonstrator.   

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This talk presents Bayesian procedures for evaluating (or ``calibrating") predictions of an experiment's sensitivity to both continuous and discrete parameters. We apply these procedures to Project 8, an experiment which aims to determine the absolute neutrino mass scale from the tritium beta decay spectrum. We evaluate sensitivity predictions by computing true and false ``claim rates" for a group of pseudo-spectra, each generated after sampling parameters from priors to weight claim rates by the probabilities of obtaining different spectra. The data are analyzed using a new Bayesian model of the beta spectrum. For a design scenario under consideration, we find Project 8 could achieve its goal of measuring the electron-weighted neutrino mass within $40\,$meV ($90\%$ credibility). Masses $>500\,$meV could be measured within $\approx5\,$meV. We validate our projections by showing that $90\%$ credible intervals contain the true neutrino mass for $(90\pm2)\%$ of datasets. In addition, we find that a next-generation beta decay experiment can potentially constrain the mass ordering. In some cases, an analysis with two neutrino states can reveal that the ordering is inverted, an unobtainable result for the traditional single-neutrino approach to beta decay analysis.   

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The Karlsruhe Tritium Neutrino (KATRIN) experiment is a sensitive probe of the neutrino mass scale, using the kinematics of tritium beta decay to target a design sensitivity of 0.2 eV (90% CL). Since KATRIN's first neutrino-mass results in 2019, which improved the world's best direct limit by a factor of about two, the collaboration has developed new improvements and operational modes to further improve its physics reach. I will give an overview of the current status and progress of the experiment, including a more intense tritium source and reduced backgrounds.   

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The best direct limit of the effective electron neutrino mass comes from the KATRIN (KArlsruhe TRItium Neutrino) experiment, which aims to measure the mass with an unprecedented design sensitivity of 0.2 eV at the 90{\%} confidence level. The neutrino is produced in tritium beta decay and its mass is derived by fitting the energy spectrum of the beta-electrons near the kinematic endpoint of 18.6 keV. Magnetic fields guide charged particles through the energy-analyzing retarding spectrometers towards the KATRIN detector. Ions from the source propagating to the spectrometers would act as a background source due to the production of secondary electrons that can be detected by the main detector. To prevent this, ions~must be blocked by electrodes. We have measured the flux of source ions for different tritium column densities and always found it below the design limit. We calibrated the ion monitoring devices. We tested the blocking efficiency of the electrodes and measured the characteristic timescale of each electrode's neutralization, resulting from secondary electrons getting trapped in the positive potentials created by them. We will share the results of these tests and the preferred settings for future neutrino-mass operations.   

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Solar neutrino experiments have had great success in furthering our understanding of the neutrino sector and the Sun. Several of these experiments, like BOREXINO, KamLAND, and SuperKamiokande, are also very sensitive to inverse beta decay, a process with a unique experimental signature initiated by antineutrinos. We explore this in our work to derive constraints on a model of light new physics that transforms a small fraction of the neutrino flux from nuclear fusion reactions in the solar core into antineutrinos. The constraints disfavor recent proposals to explain the LSND and MiniBooNE anomalies with decaying sterile neutrinos. We conclude by looking at the near future and the improved sensitivity of the current experimental program.   

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We propose a new approach to explore the neutral-current non-standard neutrino interactions (NSI) in atmospheric neutrino experiments using oscillation dips and valleys in reconstructed muon observables, at a detector like ICAL. We show that the non-zero value of NSI parameter $\varepsilon_{\mu\tau}$ shifts the oscillation dip locations in $L/E$ distributions of the up/down event ratios of reconstructed $\mu^-$ and $\mu^+$ in opposite directions. We introduce a new variable $\Delta d$ representing the difference of dip locations in $\mu^-$ and $\mu^+$, which is sensitive to $\varepsilon_{\mu\tau}$, and is independent of the value of $\Delta m^2_{32}$. We further note that the oscillation valley in the ($E$, $\cos \theta$) plane of the reconstructed muon observables bends in the presence of NSI, its curvature having opposite signs for $\mu^-$ and $\mu^+$. We illustrate how the measurement of contrast in the curvatures of valleys in $\mu^-$ and $\mu^+$ can be used to estimate $\epsmutau$. Using these proposed oscillation dip and valley measurements, the achievable precision on $|\varepsilon_{\mu\tau}|$ at 90\% C.L. is about 2\% with 500 kt$\cdot$yr exposure including the effects of statistical fluctuations, systematic errors, and uncertainties in oscillation parameters.