Abstract
We present a detailed report on sterile neutrino oscillation and U-235 antineutrino energy spectrum measurement results from the PROSPECT experiment at the highly enriched High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. In 96 calendar days of data taken at an average baseline distance of 7.9 m from the center of the 85 MW HFIR core, the PROSPECT detector has observed more than 50,000 interactions of antineutrinos produced in beta decays of U-235 fission products. New limits on the oscillation of antineutrinos to light sterile neutrinos have been set by comparing the detected energy spectra of ten reactor-detector baselines between 6.7 and 9.2 meters. Measured differences in energy spectra between baselines show no statistically significant indication of antineutrinos to sterile neutrino oscillation and disfavor the Reactor Antineutrino Anomaly best-fit point at the 2.5$\sigma$ confidence level. The reported U-235 antineutrino energy spectrum measurement shows excellent agreement with energy spectrum models generated via conversion of the measured U-235 beta spectrum, with a $\chi^2$/DOF of 31/31. PROSPECT is able to disfavor at 2.4$\sigma$ confidence level the hypothesis that U-235 antineutrinos are solely responsible for spectrum discrepancies between model and data obtained at commercial reactor cores. A data-model deviation in PROSPECT similar to that observed by commercial core experiments is preferred with respect to no observed deviation, at a 2.2$\sigma$ confidence level.
Highlights
Neutrinos arguably remain the least well-understood fundamental particles in the Standard Model: their absolute masses are only constrained within a few orders of magnitude, properties of their right-handed versions and differences between matter and antimatter versions are not fully understood, and many of their flavor mixing parameters remain uncertain at the 10% level or greater [1].Further improvement in understanding of these properties requires new high-precision measurements using highintensity neutrino sources
We present a detailed report on sterile neutrino oscillation and 235U νe energy spectrum measurement results from the PROSPECT experiment at the highly enriched High Flux Isotope Reactor (HFIR) at Oak
Improved sterile neutrino oscillation search results and an improved measurement of the reactor νe spectrum produced by 235U fission will be described, in addition to reviewing in detail how the inputs and systematic uncertainties for these two different analyses are determined
Summary
Neutrinos arguably remain the least well-understood fundamental particles in the Standard Model: their absolute masses are only constrained within a few orders of magnitude, properties of their right-handed versions and differences between matter and antimatter versions are not fully understood, and many of their flavor mixing parameters remain uncertain at the 10% level or greater [1]. The PROSPECT experiment has recently performed the first high-statistics measurement of IBD energy spectra at a highly 235U enriched reactor, with precision better than 10% between 1–6 MeV [40] These measurements confirm differing rates and energies of νe production for the different fission isotopes, and provide improved justifications for and demonstration of capabilities in monitoring the status, power, and fuel content of nuclear reactors using their νe emissions [41,42,43,44,45]. Improved sterile neutrino oscillation search results and an improved measurement of the reactor νe spectrum produced by 235U fission will be described, in addition to reviewing in detail how the inputs and systematic uncertainties for these two different analyses are determined.
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