R. D. McKeown

College of William and Mary, Williamsburg, Virginia, United States

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Publications (234)984.78 Total impact

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    ABSTRACT: The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long distances. PROSPECT is conceived as a 2-phase experiment utilizing segmented $^6$Li-doped liquid scintillator detectors for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT Phase I consists of a movable 3-ton antineutrino detector at distances of 7 - 12 m from the reactor core. It will probe the best-fit point of the $\nu_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored region of the sterile neutrino parameter space at $>$3$\sigma$ in 3 years. With a second antineutrino detector at 15 - 19 m from the reactor, Phase II of PROSPECT can probe the entire allowed parameter space below 10 eV$^{2}$ at 5$\sigma$ in 3 additional years. The measurement of the reactor antineutrino spectrum and the search for short-baseline oscillations with PROSPECT will test the origin of the spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and conclusively address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly.
    Full-text · Article · Dec 2015
  • A. Gando · D. Dwyer · C. Mauger · R. D. McKeown · C. Zhang
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    ABSTRACT: We report a measurement of the neutrino-electron elastic scattering rate of 862 keV ^7Be solar neutrinos based on a 165.4 kt d exposure of KamLAND. The observed rate is 582±94(kt d)^(−1), which corresponds to an 862-keV Be7 solar neutrino flux of (3.26±0.52)×10^9cm^(−2)s^(−1), assuming a pure electron-flavor flux. Comparing this flux with the standard solar model prediction and further assuming three-flavor mixing, a ν_e survival probability of 0.66±0.15 is determined from the KamLAND data. Utilizing a global three-flavor oscillation analysis, we obtain a total ^7Be solar neutrino flux of (5.82±1.02)×10^9cm^(−2)s^(−1), which is consistent with the standard solar model predictions.
    No preview · Article · Nov 2015
  • F. P. An · R. D. McKeown
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    ABSTRACT: We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×10^5 GW_(th) ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six ^(241)Am−^(13)C radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin 2^2θ_(13) and |Δm^2_(ee)| were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin^2 2θ_(13)=0.084±0.005 and |Δm^2_(ee)|=(2.42±0.11)×10^(−3) eV^2 in the three-neutrino framework.
    No preview · Article · Sep 2015 · Physical Review Letters
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    ABSTRACT: A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron/gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell long axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. Key design features for optimizing MeV-scale response and background rejection capabilities are identified.
    Full-text · Article · Aug 2015 · Journal of Instrumentation
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    ABSTRACT: This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9~GW$_{th}$ nuclear reactors with six detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1,579~m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296,721 and 41,589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 $\pm$ 0.04) $\times$ 10$^{-18}$~cm$^2$/GW/day or (5.92 $\pm$ 0.14) $\times$ 10$^{-43}$~cm$^2$/fission. This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is $0.946\pm0.022$ ($0.991\pm0.023$) relative to the flux predicted with the Huber+Mueller (ILL+Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2$\sigma$ over the full energy range with a local significance of up to $\sim$4$\sigma$ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
    Full-text · Article · Aug 2015
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    ABSTRACT: The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of $\bar{\nu}_e$ oscillations over km-baselines. Subsequent data has provided the world's most precise measurement of $\rm{sin}^22\theta_{13}$ and the effective mass splitting $\Delta m_{ee}^2$. The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world's most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes (PMTs), the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors' baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.
    Full-text · Article · Aug 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including $\gamma$-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. The general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein.
    No preview · Article · Jun 2015
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    ABSTRACT: We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9$\times$10$^5$ GW$_{\rm th}$-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six $^{241}$Am-$^{13}$C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of $\sin^{2}2\theta_{13}$ and $|\Delta m^2_{ee}|$ were halved as a result of these improvements. Analysis of the relative antineutrino rates and energy spectra between detectors gave $\sin^{2}2\theta_{13} = 0.084\pm0.005$ and $|\Delta m^{2}_{ee}|= (2.42\pm0.11) \times 10^{-3}$ eV$^2$ in the three-neutrino framework.
    Full-text · Article · May 2015 · Physical Review Letters
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    ABSTRACT: We describe the design and construction of the low rate neutron calibration sources used in the Daya Bay Reactor Anti-neutrino Experiment. Such sources are free of correlated gamma-neutron emission, which is essential in minimizing induced background in the anti-neutrino detector. The design characteristics have been validated in the Daya Bay anti-neutrino detector.
    Preview · Article · Apr 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • R. D. McKeown
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    ABSTRACT: The continuous electron beam accelerator facility and associated experimental equipment at Jefferson Lab comprise a unique facility for experimental nuclear physics. This facility is presently being upgraded, which will enable a new experimental program with substantial discovery potential to address important topics in nuclear, hadronic, and electroweak physics. Further in the future, it is envisioned that the Laboratory will evolve into an electron-ion colliding beam facility.
    No preview · Article · Feb 2015 · Few-Body Systems
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    R. D. McKeown
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    ABSTRACT: The Continuous Electron Beam Accelerator Facility (CEBAF) and associated experimental equipment at Jefferson Lab comprise a unique facility for experimental nuclear physics. This facility is presently being upgraded, which will enable a new experimental program with substantial discovery potential to address important topics in nuclear, hadronic, and electroweak physics. Further in the future, it is envisioned that the Laboratory will evolve into an electron-ion colliding beam facility.
    Preview · Article · Dec 2014
  • F. P. An · R. D. McKeown · R. H. M. Tsang
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    ABSTRACT: A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment’s unique configuration of multiple baselines from six 2.9 GW_(th) nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10^(−3) eV^2 < |Δm^2_(41) | < 0.3 eV^2 range. The relative spectral distortion due to the disappearance of electron antineutrinos was found to be consistent with that of the three-flavor oscillation model. The derived limits on sin^2 2θ_(14) cover the 10^(−3) eV^2 ≲ |Δm^2_(41) | ≲ 0.1eV^2 region, which was largely unexplored.
    No preview · Article · Oct 2014 · Physical Review Letters
  • F. P. An · R. D. McKeown · R. H. M. Tsang
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    ABSTRACT: A new measurement of the θ_(13) mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of the θ_(13) measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GW_(th) reactors, the rate deficit observed at the far hall is interpreted as sin^2 2θ_(13) = 0.083±0.018 in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin^2 2θ_(13) = 0.089±0.008 as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
    No preview · Article · Oct 2014
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    ABSTRACT: The dependence on Q2 (the negative square of the 4-momentum of the exchanged virtual photon) of the generalised Gerasimov–Drell–Hearn integral for the proton has been measured in the range 1.2 GeV2<Q2<12 GeV2 by scattering longitudinally polarised positrons on a longitudinally polarised hydrogen gas target. The contributions of the nucleon-resonance and deep inelastic regions to this integral have been evaluated separately. The latter has been found to dominate for Q2>3 GeV2, while both contributions are important at low Q2. The total integral shows no significant deviation from a 1/Q2 behaviour in the measured Q2 range, and thus no sign of large effects due to either nucleon-resonance excitations or nonleading twist.
    Full-text · Article · Sep 2014 · Physics Letters B
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    ABSTRACT: Evidence for a positive longitudinal double-spin asymmetry 〈A1ρ〉=0.24±0.11stat±0.02syst in the cross section for exclusive diffractive ρ0(770) vector–meson production in polarised lepton–proton scattering was observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA positron beam was scattered off a longitudinally polarised pure hydrogen gas target. The average invariant mass of the photon–proton system has a value of 〈W〉=4.9 GeV, while the average negative squared four-momentum of the virtual photon is 〈Q2〉=1.7 GeV2. The ratio of the present result to the corresponding spin asymmetry in inclusive deep-inelastic scattering is in agreement with an early theoretical prediction based on the generalised vector–meson dominance model.
    Full-text · Article · Sep 2014 · Physics Letters B
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    ABSTRACT: Measurements of the individual multiplicities of pi /sup +/, pi /sup -/ and pi /sup 0/ produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion multiplicity is the same as for neutral pions, up to z approximately= 0.7, where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below z approximately= 0.7) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is 0.51 +or- 0.01(stat.) +or- 0.08 (syst.) and 0.26 +or- 0.01(stat.) +or- 0.04(syst.), respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer Q/sup 2/ and the Bjorken variable x. The observed dependence on Q/sup 2/ agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected Q/sup 2/-dependence.
    Full-text · Article · Sep 2014 · European Physical Journal C
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    ABSTRACT: A search for light sterile neutrino mixing was performed with the first 217 days of data from the Daya Bay Reactor Antineutrino Experiment. The experiment's unique configuration of multiple baselines from six 2.9~GW$_{\rm th}$ nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1579~m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the $10^{\rm -3}~{\rm eV}^{2} < |\Delta m_{41}^{2}| < 0.3~{\rm eV}^{2}$ range. The relative spectral distortion due to electron antineutrino disappearance was found to be consistent with that of the three-flavor oscillation model. The derived limits on $\sin^22\theta_{14}$ cover the $10^{-3}~{\rm eV}^{2} \lesssim |\Delta m^{2}_{41}| \lesssim 0.1~{\rm eV}^{2}$ region, which was largely unexplored.
    Full-text · Article · Jul 2014 · Physical Review Letters
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    ABSTRACT: We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable's motion, and the system was controlled via a graphical user interface.
    Full-text · Article · Jul 2014
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    ABSTRACT: A new measurement of the $\theta_{13}$ mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely different systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of $\theta_{13}$ measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GW$_{th}$ reactors, the rate deficit observed at the far hall is interpreted as $\sin^22\theta_{13}=0.083\pm0.018$ in the three-flavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain $\sin^22\theta_{13}=0.089\pm0.008$ as the final result for the six-antineutrino-detector configuration of the Daya Bay experiment.
    Full-text · Article · Jun 2014 · Physical Review D
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    ABSTRACT: We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.
    Full-text · Article · May 2014 · Physical Review C

Publication Stats

6k Citations
984.78 Total Impact Points

Institutions

  • 2005-2015
    • College of William and Mary
      • Department of Physics
      Williamsburg, Virginia, United States
  • 2010-2014
    • Thomas Jefferson National Accelerator Facility
      • Division of Physics
      Ньюпорт-Ньюс, Virginia, United States
  • 2000-2014
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 1981-2014
    • California Institute of Technology
      • Department of Physics
      Pasadena, California, United States
  • 2005-2006
    • Tohoku University
      • Research Center for Neutrino Science
      Sendai-shi, Miyagi-ken, Japan
  • 2002
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 2001
    • University of Ferrara
      • Department of Physics and Earth Sciences
      Ferrare, Emilia-Romagna, Italy
  • 1999-2000
    • Ghent University
      • Department of Physics and Astronomy
      Gand, Flanders, Belgium
  • 1998
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      Erlangen, Bavaria, Germany
  • 1997
    • Hampton University
      • Department of Physics
      Hampton, VA, United States
  • 1980-1987
    • Argonne National Laboratory
      • Division of Physics
      Lemont, Illinois, United States
  • 1982
    • University of Illinois, Urbana-Champaign
      • Department of Physics
      Urbana, Illinois, United States