Session LN: Neutrino Physics IV

Search for Invisible Nucleon Decay in the SNO+ Light Water Phase

Many Grand Unified Theories predict processes that would allow baryons to decay to leptons, violating baryon number conservation.  The observation of baryon number violation in nucleon decay would be a revelation as well as being pivotal in understanding the apparent asymmetry between baryons and anti-baryons in the universe.  This is manifest in some theories primarily through the decay of nucleons to three chargeless leptons (e.g. n -> 3ν), which can only be observed through the resulting nuclear deexcitation gamma. This "invisible" nucleon decay could be observable in water through the deexcitation of the resulting oxygen-15 nucleus which emits a 6.2 MeV gamma and requires that backgrounds at these energies, in a large detector, to be extremely low. Presented here are the first results from the SNO+ light water phase which consists of nearly 120 days of live data taking. A blind analysis was performed using a Poisson counting method and a maximum likelihood method independently to obtain the results.   

Constraints on Neutrino Lifetime from the Sudbury Neutrino Observatory

As neutrinos are known to have a finite mass it is possible with new physics that neutrinos could decay to lighter states. On the long baseline between the Earth and the Sun, such decay could lead to an energy dependent disappearance of the solar neutrino flux. An analysis of SNO data has been developed to constrain the lifetime of neutrino mass state two by fitting for this energy dependent distortion to the survival probability of 8B solar neutrinos.
  

A Neutrino Disappearance Search for Sterile Neutrinos with the CAPTAIN-Mills Detector at the Los Alamos Neutron Science Center

MiniBooNE and LSND have shown compelling evidence for sterile neutrinos at Δm² ∼1 eV² in short baseline neutrino oscillations experiments. In these experiments, a pure muon neutrino beam is used to search for electron neutrino appearance, but muon neutrino disappearance searches have shown no anomalies. This talk will describe the CAPTAIN-Mills experiment which will use a 10-ton liquid argon scintillation detector to leverage the enhanced cross section from coherent elastic neutrino-nucleus scattering (CEvNS) to measure muon neutrino disappearance at the Lujan Center at the Los Alamos Neutron Science Center. Lujan is a 100-kW stopped pion source that nominally delivers a 290-ns wide, 800-MeV proton beam onto a tungsten target at 20 Hz, but the beam width can be significantly narrowed to 30 ns. Fast pulsing is critical for isolating the monoenergetic muon neutrino from the other neutrino flavors and neutron backgrounds. In this talk, I will describe the CAPTAIN-Mills detector, the Lujan neutrino source, the expected sensitivities for sterile neutrinos, and show results from the summer neutrino test run. 

Neutrino Quantum Kinetics in the Early Universe

Neutrinos decouple from the plasma at a temperature scale of 1 MeV in the early universe. The decoupling is an out-of-equilibrium process and requires the solution of the Quantum Kinetic Equations (QKEs) in a homogeneous and isotropic geometry. We present results from our code BURST on solving the complete set of QKEs relevant for neutrino energy transport. By using generalized density matrices, we follow the non-degenerate spectra of electron, muon, and tau flavor neutrinos. In addition, we are able to show how the coherence between the flavor states manifests itself in the off-diagonal elements of the density matrices. Our results have implications for both the primordial abundances predicted from big bang nucleosynthesis and neutrino observables in the cosmic microwave background.   

Spectral analysis for the MAJORANA DEMONSTRATOR

The MAJORANA DEMONSTRATOR is an experiment searching for neutrinoless double-beta decay in ⁷⁶Ge.  It consists of two modular arrays of natural and ⁷⁶Ge-enriched high purity germanium detectors totalling 44.1 kg, operating on the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA.  The ultra-low background achieved by the MAJORANA DEMONSTRATOR has an expected variation in measured rates among each constituent detector.  I will discuss studies into how the geometrical distribution of background rates may be exploited to improve spectral analysis sensitivity, and statistical approaches used to analyze the measured spectrum.   

Extensions of Higgs Universality in the Sterile Neutrino Sector

Application of Higgs Universality to the neutrino sector provides coupling between the active neutrino sector and the sterile neutrino sector. For either Hierarchy, this leads to predictions for the mass ratios in the sterile sector.  While the most natural result is that the ratios of sterile masses should be approximately the squares of the ratios of charged fermions, the ratios of the lighter masses can be modified.  We show how these results are obtained.