Session C08: Neutrino Physics: Results and New Initiatives I

Resolving DUNE oscillation parameter ambiguities in the 3+1 sterile neutrino scenario using SBN

There has been significant interest in the possible effect that one or more light sterile neutrinos, hinted by several short-baseline neutrino oscillation experiments, can have on the measurement of the three-neutrino mixing parameters at the future long-baseline Deep Underground Neutrino Experiment (DUNE), with a particular focus on their effect on CP-violation measurements. By the time DUNE is operational, however, the Short-Baseline Neutrino (SBN) program at Fermilab will have performed high-precision measurements of possible light sterile neutrino oscillations, or will have provided stringent constraints to such scenarios. In this work we will present results on a joint SBN+DUNE light sterile neutrino oscillation analysis, combining both $\nu_{e}$ appearance and $\nu_{\mu}$ disappearance oscillation measurements at both long and short baselines. By utilizing a fast MonteCarlo simulation of all SBN and DUNE detectors, we estimate the effects that either a positive or a null observation at SBN could have on DUNE sensitivities.   

Short-baseline Sterile Neutrino Searches Using the NOvA Near Detector

Three-flavor neutrino oscillations have successfully explained a wide range of neutrino oscillation data. However, the excess of events as seen by the LSND and MiniBooNE experiments and the deficit of events seen at the GALLEX and SAGE experiments when exposed to a calibration source can be explained if a new sterile neutrino state with a mass near 1 eV exists. While these results are tantalizing, they are not conclusive, as they are in tension with null results from other experiments. Resolving the issue of the existence of light sterile neutrinos has profound implications for both particle physics and cosmology. The NOvA Near Detector is a 293 ton, almost fully-active, fine-grained liquid-scintillator detector which may be able to clarify this situation by searching for sterile-driven oscillations of neutrinos from the NuMI beam over a baseline of 1 km. I will discuss two short-baseline searches. The first looks for muon-neutrino disappearance and electron-neutrino appearance using neutrinos from the narrow-band beam peaked at 2 GeV. This analysis probes the L/E range where oscillations should occur if the LSND and MiniBooNE anomalies were due to sterile neutrinos. The second looks for tau-neutrino appearance in the secondary, high-energy beam peak due to kaon decays.   

Planned Improvements to Sterile Neutrino Searches in the NOvA Far Detector

The evidence of neutrino oscillations from the majority of neutrino oscillation experiments are consistent with a three-flavor model, but the existence of additional sterile neutrino flavors is required to explain deviations observed in short-baseline experiments, such as LSND and MiniBooNE, in terms of neutrino oscillations. The NOvA experiment, which uses a long baseline of 810 km between its Near Detector (ND) at Fermilab and Far Detector (FD) in Minnesota, has the potential to search for sterile neutrino mixing by looking for a deficit of neutral-current (NC) neutrino interactions at the FD with respect to the ND prediction. In this talk, I will present the scope of the future planned 2018 NC analysis and will also present the improvements being developed for the NC sterile neutrino search. These analysis improvements include a simultaneous ND-FD shape fit of the NC energy spectrum, allowing NOvA to probe a wider range of sterile neutrino masses than previous analyses.   

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

The LSND and MiniBooNE short baseline neutrino oscillation experiments have shown evidence for sterile neutrinos at $\Delta m^2 \sim 1$ eV$^2$. Both experiments used pure muon neutrino beams to search for electron neutrino appearance, i.e., $\nu _\mu \rightarrow \nu _e$, yet corresponding disappearance experiments have shown no anomalies. We will deploy the CAPTAIN-Mills detector, a 7-ton fiducial volume, single-phase, liquid argon scintillation detector, and use the coherent elastic neutrino-nucleus scattering (CE$\nu$NS) process to measure muon neutrino disappearance at the Lujan Facility at the Los Alamos Neutron Science Center. Using CE$\nu$NS greatly enhances the event rate compared to other oscillation experiments. Lujan is a 100-kW stopped pion source that nominally delivers a 250-ns wide, 800-MeV proton beam onto a tungsten target at 30 Hz, but the beam width can be significantly narrowed to 30 ns. Lujan's fast pulsing is advantageous for isolating the prompt 30-MeV muon neutrino from the delayed muon-decay neutrinos 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 our neutron background survey.   

Fine Structure in the Antineutrino Spectrum Generated by a Nuclear Reactor

The antineutrino spectrum generated by a nuclear reactor is the sum of the spectra from about 800 fission products. For energies higher than the Inverse Beta Decay cross section threshold, about 100 fission products contribute about 90{\%} of the spectrum. Therefore, we would expect deviations from the smooth Huber-Mueller shape due to (a) the contribution of a strongly populated fission product, (b) sharp cutoffs in the individual antineutrino spectra, and (c) the contribution from a small number of fission products with similar end-point energy, effectively resembling the first case. A novel way of numerically revealing these deviations was developed, which consists of plotting the ratio of adjacent points in the antineutrino spectrum. We find that with a binning interval of 0.1 MeV or less, the observation of sharp cutoffs from the individual spectra could be attained. Remarkably, even with a binning of 0.25 MeV, we detect a peak-like feature in the ratio plot, which we attribute to the decay of 4 nuclides. We also explore the possibility of revealing contributions from individual fission products in the electron spectra measured at the Institut Laue-Langevin following the neutron induced fission of $^{\mathrm{235}}$U and $^{\mathrm{239,241}}$Pu.   

Assembly and Installation of the PROSPECT Short-Baseline Antineutrino Detector

PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a short-baseline reactor antineutrino experiment designed to precisely measure the fission generated antineutrino spectrum of $^{235}$U utilizing an optically segmented 4-ton $^6$Li liquid scintillator target. This measurement will enable a further investigation of the origin of discrepancies between measured and predicted reactor antineutrino fluxes and spectra while simultaneously probing the possible existence of eV$^2$-scale sterile neutrino oscillations independent of the underlying reactor antineutrino flux models. The PROSPECT detector was completed in late 2017, and began taking physics data in 2018 at the High Flux Isotope Reactor at the Oak Ridge National Laboratory. This talk will provide an introduction to PROSPECT’s experimental setup and physics goals, while highlighting the design, assembly and deployment of the antineutrino detector.   

Pulse Shape Discriminating $^6$Li-Doped Liquid Scintillator for the PROSPECT Experiment

PROSPECT is a reactor antineutrino experiment consisting of a segmented $^6$Li-doped liquid scintillator antineutrino detector. The experiment, located at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, will begin physics data-taking in early 2018. To enable the reduction of copious cosmogenic backgrounds to the inverse beta decay antineutrino interaction signal, the PROSPECT collaboration has developed and produced a custom $^6$Li-doped liquid scintillator with powerful pulse-shape discrimination capabilities. In this talk, we will report the properties of the PROSPECT liquid scintillator and production of 5 tons of scintillator necessary for the operation of the PROSPECT experiment. We will also describe a novel $^2^2^7$Ac doping mechanism for in situ energy calibration and measurement of the relative efficiency of detector segments.   

Simulating Calibrations and Energy Response in the PROSPECT Detector

The PROSPECT experiment utilizes a 1.2 x 1.6 x 2.0 m$^{3}$ segmented liquid scintillator antineutrino detector to probe short-baseline neutrino oscillations and precisely measure the antineutrino spectrum of the primary fission isotope $^{235}$U. The PROSPECT antineutrino detector, located at a closest distance of $\sim$ 7 meters from the High Flux Isotope Reactor (HFIR) at Oak Ridge National Lab, began physics data-taking in early 2018. A precision measurement of the antineutrino energy spectrum, as well as any oscillation-induced distortions to that energy spectrum in a relatively compact detector, the energy response in all 154 segments of the PROSPECT detector must be well characterized. For PROSPECT, this will be achieved via comparison of detector-internal calibration source and intrinsic background data to Monte Carlo modeling of these sources in the Geant4 platform. This talk will provide an introduction to the PROSPECT computing environment and simulation and data analysis framework, and will utilize PROSPECT Monte Carlo simulation data to demonstrate aspects of PROSPECT’s expected energy response.   

Calibration and Initial Performance of the PROSPECT Detector

PROSPECT, the Precision Reactor Oscillation and Spectrum Experiment, consists of a segmented liquid scintillator antineutrino detector designed to probe short-baseline neutrino oscillations and precisely measure the antineutrino spectrum of the primary fission isotope U-235 at the High Flux Isotope Reactor at Oak Ridge National Laboratory. To achieve these physics goals, precise understanding of the energy response in each of 154 individual segments is essential. PROSPECT uses a distributed array of optical and radioactive sources to understand the detector response. This talk will describe the design and implementation of PROSPECT's calibration systems and provide a first look at calibration and performance of the detector.