Recent Physics Results from the PROSPECT Reactor Antineutrino Experiment
Manoa Andriamirado (IIT)
On behalf of the Collaboration
Phys. Rev. D 104, 012009 Phys. Rev. D 103, 032001
Motivation
● Antineutrino flux from reactor shows ~6%
deficiency with respect to prediction.
● Oscillation of antineutrino into a 4th flavor, sterile neutrino.
● Precision measurement at short-baseline can help to observe any sign of sterile neutrino oscillation.
● Distortion in the antineutrino energy spectrum (bump), at 5MeV from LEU reactor.
● Learn by burning different fuel.
● Measurement of antineutrino energy spectrum from Highly-Enriched-Uranium (HEU).
PROSPECT Experimental setup
● Covers 7-10m baseline from a compact HEU reactor core.
● The HEU reactor: 20cmx50cm, burns 235U only.
● Deployed on surface with non-negligible environmental backgrounds.
● ~4-ton 6Li-doped PSD-capable liquid scintillator.
● Array of 11x14 optically isolated segments.
● Segment attached to PMT at each end for light readout.
● Energy resolution: 4.5%-5%/√E.
Reactor
core
PROSPECT design features
● Detection of antineutrino through Inverse-Beta- Decay (IBD).
● Prompt energy gives an estimate of energy.
● Neutron capture on Li for tagging IBD signal.
● Waveforms from both PMTs are combined into pulse with physical reconstructed variables.
● Particle Identification with PSD:
● Discern particles signature: γ, neutron capture, proton recoil, nuclear recoil.
● Crucial for event selection.
IBD event selection
● 95.65 reactor-on calendar days, 73.09 reactor-off dataset.
● Select e+-like events followed by n-Li capture events.
● Reject IBD-like events coincident with cosmic muon/neutron events.
● Reject IBD-like events from non-fiducialized segments and segments with PMT current instabilities.
● Background reduction ~3-4 order of magnitude.
Sterile neutrino oscillation
● Combine a group of segments into a baseline.
● Compare each baseline spectrum to the full- detector spectrum.
No obvious sign of oscillation
Sterile neutrino exclusion region
● Compare measured to predicted spectrum ratios for different oscillation parameters.
● Chi-square test:
● Covariance matrix: Vtot = Vstat + Vsys
● Best fit point of 119.3/142 at (sin22θ14, ∆m2) = (0.11,1.78 eV2)
● Use CLs method and Feldman-Cousin to determine the excluded region.
● PROPSECT’s data compatible with the no-oscillation hypothesis (p = 0.57).
● RAA best-fit point excluded at 98.5% C.L.
235 U antineutrino measurement
● Integrate spectrum over the baseline.
● PROSPECT’s data has a good agreement with the Huber-Mueller model.
● χ2/ndf = 30.79/31.
● Add DYB bump fit to HM model.
● Disfavored no-bump and all-bump from 235U at 2.2σ and 2.44σ respectively.
● A best-fit of 0.84±0.39 is observed
o 235 U bump ig235 U bump
LEU and HEU reactors both see the same bump!
Boosted dark matter search
● Light dark matter gains kinetic energy from CR-DM scattering to be detectable in neutrino experiment.
● Use numerical simulation to propagate DM through the atmosphere to the detector.
● DM scatters off of a free proton inside the detector and leave a high PSD single pulse event.
● DM flux varies as the Earth rotates:
● High signal period: 22:00 – 02:00 GMST
● Low signal period: 10:00 – 14:00 GMST (high σχ
DMblocked by the Earth’s bulk)
DM-like event signal
● 14.6 solar-days reactor-off dataset.
● Apply a set of cuts/vetoes to select signals and remove backgrounds.
● Background reduced by 2.5-3.5 order of magnitude.
● Divide DM-like spectrum into an hourly-rate.
● No obvious sign of modulation in the detector.
Dark matter exclusion region
● PROSPECT’s result covers new space previously un-probed by other terrestrial experiments.
● Upper limit of exclusion is limited by DM attenuation in the atmosphere.
● Lower limit is limited by the fraction of DM interacting with the detector.
Summary
● PROSPECT’s data is compatible with the no-oscillation hypothesis.
● No evidence for sterile neutrino oscillations is found.
● The ‘reactor antineutrino anomaly’ best-fit is excluded at 2.5σ CL.
● PROSPECT’s 235U measurement has a good agreement with the Huber-Mueller model.
● ‘No 235U bump’ is disfavored at 2.2σ CL.
● 235U being solely responsible for the bump is disfavor at 2.4σ CL.
● PROSPECT’s unique configurations allow to probe regions of dark matter phase space unaddressed by any previous terrestrial experiments.
● Data does not exhibit sidereal diurnal modulation.
● Complementary to cosmological DM limits.