Bulletin of the American Physical Society
2020 Fall Meeting of the APS Division of Nuclear Physics
Volume 65, Number 12
Thursday–Sunday, October 29–November 1 2020; Time Zone: Central Time, USA
Session EG: Reactor and Short Baseline Neutrino Experiments |
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Chair: Vincenzo Cirigliano, LANL |
Friday, October 30, 2020 10:30AM - 10:42AM |
EG.00001: PROSPECT's latest results for Sterile Neutrino Oscillation search Jose Palomino Gallo, Bryce Littlejohn PROSPECT, the Precision Reactor Oscillation and SPECTrum experiment, is a reactor antineutrino experiment consisting 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 from the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). PROSPECT uses a 4-ton optically segmented, Li6-loaded liquid scintillator detector with high light yield, world-leading energy resolution, and excellent pulse shape discrimination. PROSPECT’s neutrino oscillation analysis looks for differences in measured inverse beta decay (IBD) positron spectra at different positions in its detector. With a current baseline coverage of between 7 and 9 meters, the analysis search for sterile oscillations in the ~1-10 eV$^2$ mass-splitting range, with sensitivities largely independent of the underlying reactor antineutrino flux. We will summarize PROSPECT’s latest oscillation analysis results. [Preview Abstract] |
Friday, October 30, 2020 10:42AM - 10:54AM |
EG.00002: The PROSPECT $^{235}$U Antineutrino Spectrum Measurement and its Nuclear Physics Impact Benjamin Foust The Precision Reactor Oscillation and SPECTrum experiment, or PROSPECT, detector is designed to accurately measure the $^{235}$U antineutrino energy spectrum. The detector is comprised of 4 tons of Lithium-loaded liquid scintillator with 154 optically separated segments, and achieves excellent pulse-shape discrimination and particle identification. The experiment is located at the High Flux Isotope Reactor (HFIR), an 85 MW$_{Th}$ highly-enriched uranium (HEU) reactor with short reactor-on periods, such that over 99\% of the antineutrino flux comes from $^{235}$U. In this talk, I present the latest spectrum results from PROSPECT and their impact to nuclear physics. We compare the resulting spectrum to model predictions, and test the contribution of $^{235}$U towards potential high energy excess as seen in previous spectrum measurements performed at nuclear power reactors. [Preview Abstract] |
Friday, October 30, 2020 10:54AM - 11:06AM |
EG.00003: Joint Isotope-Dependent Analysis of the Daya Bay, PROSPECT, and STEREO Reactor Antineutrino Spectra Jeremy Gaison The Daya Bay, PROSPECT, and STEREO experiments have made world leading measurements of the $^{235}$U antineutrino fission spectrum using liquid scintillator detectors located at nuclear reactors. The Daya Bay experiment has detected $\sim$3.5 million antineutrinos generated from power reactors fueled by a mixture of isotopic fuels, and PROSPECT and STEREO have detected $\sim$50,000 and $\sim$40,000 antineutrinos respectively generated by research reactors with highly enriched $^{235}$U fuel. By leveraging the two independent $^{235}$U measurements and the high-statistics Daya Bay measurement, both a more precise measurement of $^{235}$U as well as a better deconvolution of the power reactor fission spectrum into its individual isotopic components are possible. In this talk, I will present the current status of the joint spectral analyses between these experiments. [Preview Abstract] |
Friday, October 30, 2020 11:06AM - 11:18AM |
EG.00004: Improving PROSPECT Oscillation and Spectrum Measurements with Single End Event Reconstruction Xianyi Zhang Current discrepancies in the reactor antineutrino flux and spectrum between experimental measurements and models hint at possible oscillations involving a sterile neutrino, and/or misunderstanding of neutrino production in nuclear reactors. PROSPECT, the Precision Reactor Oscillation and Spectrum experiment, aims to investigate the cause of these discrepancies by measuring various short baseline antineutrino spectra from the $^{235}$U-enriched High Flux Isotope Reactor at Oak Ridge National Laboratory. PROSPECT has operated a 4-ton segmented 6Li-loaded liquid scintillator detector, where each end of all longitudinal segments is coupled to a photomultiplier tube (PMT). Updated short baseline oscillation and $^{235}$U antineutrino spectrum measurements have recently been released. However, a subset of PMTs were unable to operate during the entire data acquisition period used. Here, we also describe the calibration and event reconstruction efforts made to improve the sensitivity of PROSPECT physics measurements using pulse shape information collected in segments with a single functional PMT. [Preview Abstract] |
Friday, October 30, 2020 11:18AM - 11:30AM |
EG.00005: PROSPECT-II: Extending Scientific Reach through Upgraded Performance and Multisite Operation H. Pieter Mumm The first phase of the Precision Reactor Oscillation and Spectrum (PROSPECT) experiment provided new limits on sterile neutrino oscillation at the eV$^2$ scale and a high-resolution measurement of the antineutrino spectrum due purely to $^{235}$U fission daughters. These goals remain well motivated by persistent discrepancies between measurement and prediction of both reactor flux and spectral shape. Leveraging this initial success, the PROSPECT collaboration is planning an upgraded detector that enables an expanded scientific program. An initial deployment at the High Flux Isotope Reactor will substantially enhance sensitivity to oscillation parameter space required for interpretation of long-baseline neutrino oscillation experiments and, through greatly improved statistical precision in the spectrum, provide complementary data constraining uncertainties in nuclear data for neutron rich fission daughters. A second, systematically-correlated deployment at a low-enriched-uranium reactor, would significantly improve the scientific reach of both measurements. We discuss this extended PROSPECT physics program. [Preview Abstract] |
Friday, October 30, 2020 11:30AM - 11:42AM |
EG.00006: Reactor antineutrinos with SNO+ Tanner Kaptanoglu Historically, the detection of antineutrinos produced in nuclear reactors has been instrumental in confirming neutrino oscillations and measuring neutrino mixing parameters. These reactor antineutrinos have never been observed in a pure water Cherenkov detector, where they interact primarily through inverse beta decay. In this talk, I present a search for reactor antineutrinos using data taken with the SNO+ detector while it was filled with ultra pure water. Importantly, as a water Cherenkov detector, SNO+ achieved unprecedentedly low trigger thresholds and low levels of radioactive backgrounds, which together enable this search. The method I will outline is the lowest-energy analysis of water Cherenkov neutrino detectors ever performed. [Preview Abstract] |
Friday, October 30, 2020 11:42AM - 11:54AM |
EG.00007: Machine Learning Applications for Reactor Antineutrino Detection at PROSPECT Andrea Delgado PROSPECT is an antineutrino detector located above ground at the High-Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The energy spectrum of antineutrinos emitted from the reactors is measured by using a delayed coincidence technique through the inverse-beta-decay reaction (IBD). The ORNL group is currently exploring several applications of machine learning techniques for the reconstruction and analysis of antineutrino events. In this talk, an overview of these efforts will be presented. Specifically, the use of the individual distribution of the observables of positron and neutron signals in IBD’s can be used as input to train a neural network to discriminate between true IBD interactions and accidental correlations. Additionally, we designed an encoder-decoder architecture for sequence prediction based on recurrent neural networks (RNNs). This method will allow us to match detector pulses to reconstruct the IBD interaction. [Preview Abstract] |
Friday, October 30, 2020 11:54AM - 12:06PM |
EG.00008: Effects of new $^{238}$U fission yields data on reactor antineutrino spectra Andrea Mattera, Alejandro A. Sonzogni, Elizabeth A. McCutchan, Ryan Lorek, Shaofei Zhu, Matteo Vorabbi, Gino Fabricante, Tunisia Solomon The reactor antineutrino anomaly is a decade-long puzzle, identified when improved calculations led to a $\approx$~5\% overall shortfall in the antineutrino flux, as well as an excess of antineutrinos at 5~MeV - colloquially known as 'the bump' - in all short-baseline experiments. \\ It has recently been speculated by A.C.~Hayes and collaborators that 'the bump' could be due to deficient knowledge of the $^{238}$U antineutrino spectrum. Fission yields (FYs) are, along with decay data, the key quantity needed to predict reactor antineutrino spectra, but the last evaluation of $^{238}$U dates back to the 1990's. \\ We started from new experimental data, measured with innovative experimental techniques such as inverse kinematics, and we corrected and constrained them using fission models and historical high-quality measurements. We present here several $^{238}$U FY distributions and their effects on reactor antineutrino spectra. [Preview Abstract] |
Friday, October 30, 2020 12:06PM - 12:18PM |
EG.00009: Background Characterization at HFIR for Reactor Antineutrino Measurements Blaine Heffron, Corey Gilbert, Alfredo Galindo-Uribarri Surface based reactor antineutrino experiments are challenging due to backgrounds from cosmic rays and reactor processes. Therefore it is important to measure these backgrounds with and without shielding to determine the feasibility of antineutrino detection. Currently, both inverse-beta decay and coherent elastic neutrino nucleus scattering are both physical processes used to detect antineutrinos. Oak Ridge National Laboratory houses the High Flux Isotope Reactor (HFIR), an 85 MW research reactor with a fuel composition consisting of highly enriched 235U. Both in situ measurements at the experimental site within HFIR and simulations using the MCNP and GEANT4 codes are described. [Preview Abstract] |
Friday, October 30, 2020 12:18PM - 12:30PM |
EG.00010: Li6-doped PSD Plastic Scintillators for Reactor Antineutrino Detectors Viacheslav Li In recent years, significant progress has been made at LLNL in synthesizing a new class of plastic scintillators that support Pulse Shape Discrimination (PSD) and Li-6 doping. Two distinct chemistries have been developed to solubilize Li-6 compounds in organic solvents, in which they are typically insoluble. Elements as large as 40cm have been produced, with efforts continuing to improve manufacturing procedures for larger components. These developments open new opportunities in fast and thermal neutron detection, as well as for reactor antineutrino detectors. Plastic PSD scintillator materials can enable new detector geometries, potentially reduce system complexity, and are straightforward to handle and transport. In this presentation, we will describe the materials and performance metrics. Material performance will be described in the context of the Segmented AntiNeutrino Directional Detector (SANDD), a 64-segment Li6-doped plastic scintillator detector with SiPM readout which would have otherwise been difficult or impossible to realize. [Preview Abstract] |
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