R. D. McKeown

Publications (99)254.24 Total impact

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  Available from: Sarkis Taroian

  Article: Measurement of the neutron spin structure function g1(n) with a polarized He-3 internal target HERMES Collaboration

  K. Ackerstaff, A. Airapetian, I. Akushevich, N. Akopov, M. Amarian, E.C. Aschenauer, R. Avakian, H. Avakian, A. Avetisian, B. Bains, [......], M.C. Vetterli, E. Volk, W. Wander, T.P. Welch, S.E. Williamson, T. Wise, T. Wolfel, K. Zapfe-Duren, G. Zograbian, R. Zurmuhle
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  ABSTRACT: Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function g1 n(x,Q 2) in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized 3He internal gas target. The data cover the kinematic range 0.023<x<0.6 and 1(GeV/c) 2<Q 2<15(GeV/c) 2. The integral ∫0.023 0.6g1 n(x)dx evaluated at a fixed Q 2 of 2.5(GeV/c) 2 is −0.034±0.013(stat.)±0.005(syst.). Assuming Regge behavior at low x, the first moment Γ1 n=∫0 1g1 n(x)dx is −0.037±0.013(stat.)±0.005(syst.)±0.006(extrapol.).
  Physics Letters B 02/2013; 404(3-4):383-389. · 3.95 Impact Factor
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  Available from: Sarkis Taroian

  Article: Nuclear effects on R = sigma(L) / sigma(T) in deep inelastic scattering

  K. Ackerstaff, A. Airapetian, N. Akopov, I. Akushevich, M. Amarian, E.C. Aschenauer, H. Avakian, R. Avakian, A. Avetisian, B. Bains, [......], M.G. Vincter, J. Visser, E. Volk, W. Wander, J. Wendland, S.E. Williamson, T. Wise, K. Woller, S. Yoneyama, H. Zohrabian
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  ABSTRACT: Cross section ratios for deep-inelastic scattering from 14N and 3He with respect to 2H have been measured by the HERMES experiment at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable x between 0.013 and 0.65, while the negative squared four-momentum transfer Q^2 varies from 0.5 to 15 GeV^2. The data are compared to measurements performed by NMC, E665, and SLAC on 4He and 12C, and are found to be different for x < 0.06 and Q^2 < 1.5 GeV^2. The observed difference is attributed to an A-dependence of the ratio R = sigma_L / sigma_T of longitudinal to transverse deep-inelastic scattering cross sections at low x and low Q^2.
  Physics Letters B 02/2013; 475:386-394. · 3.95 Impact Factor
• Article: First Measurement of the Neutral Current Excitation of the Delta Resonance on a Proton Target

  Collaboration, D. Androic, D. S. Armstrong, J. Arvieux, S. L. Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, [......], M. Stutzman, R. Suleiman, V. Tadevosyan, W. T. H. van Oers, M. Versteegen, E. Voutier, W. Vulcan, S. P. Wells, S. E. Williamson, S. A. Wood
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  ABSTRACT: The parity-violating asymmetry arising from inelastic electron-nucleon scattering at backward angle (~95 degrees) near the Delta(1232) resonance has been measured using a hydrogen target. From this asymmetry, we extracted the axial transition form factor G^A_{N\Delta}, a function of the axial Adler form factors C^A_i. Though G^A_{N\Delta} has been previously studied using charged current reactions, this is the first measurement of the weak neutral current excitation of the Delta using a proton target. For Q^2 = 0.34 (GeV/c)^2 and W = 1.18 GeV, the asymmetry was measured to be -33.4 \pm (5.3)_{stat} \pm (5.1)_{sys} ppm. The value of G^A_{N\Delta} determined from the hydrogen asymmetry was -0.05 \pm (0.35)_{stat} \pm (0.34)_{sys} \pm (0.06)_{theory}. These findings agree within errors with theoretical predictions for both the total asymmetry and the form factor. In addition to the hydrogen measurement, the asymmetry was measured at the same kinematics using a deuterium target. The asymmetry for deuterium was determined to be -43.6 \pm (14.6)_{stat} \pm (6.2)_{sys} ppm.
  12/2012;
• Article: Parity-Violating Electron Scattering and the Electric and Magnetic Strange Form Factors of the Nucleon

  D. S. Armstrong, R. D. McKeown
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  ABSTRACT: Measurement of the neutral weak vector form factors of the nucleon provides unique access to the strange quark content of the nucleon. These form factors can be studied using parity-violating electron scattering. A comprehensive program of experiments has been performed at three accelerator laboratories to determine the role of strange quarks in the electromagnetic form factors of the nucleon. This article reviews the remarkable technical progress associated with this program, describes the various methods used in the different experiments, and summarizes the physics results along with recent theoretical calculations.
  07/2012;
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  Available from: Elizabeth Beise

  Article: Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], M Stutzman, R Suleiman, V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood
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  ABSTRACT: The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2  ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03  ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.
  Physical Review Letters 03/2012; 108(12):122002. · 7.37 Impact Factor
• Article: Search for Extraterrestrial Antineutrino Sources with the KamLAND Detector

  A. Gando, Y. Gando, K. Ichimura, H. Ikeda, K. Inoue, Y. Kibe, Y. Kishimoto, M. Koga, Y. Minekawa, T. Mitsui, [......], K. E. Downum, G. Gratta, Y. Efremenko, Y. Kamyshkov, O. Perevozchikov, H. J. Karwowski, D. M. Markoff, W. Tornow, K. M. Heeger, and M. P. Decowski
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  ABSTRACT: We present the results of a search for extraterrestrial electron antineutrinos ('s) in the energy range using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8B solar ν e 's converting into 's at 5.3 × 10–5 (90% CL), if we assume an undistorted shape. This limit corresponds to a solar flux of 93 cm–2 s–1 or an event rate of 1.6 events (kton – year)–1 above the energy threshold . The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles.
  The Astrophysical Journal 01/2012; 745(2):193. · 6.02 Impact Factor
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  Available from: Brian Fujikawa

  Article: Partial radiogenic heat model for Earth revealed by geoneutrino measurements

  Kamland Collaboration, A. Gando, Y. Gando, K. Ichimura, H. Ikeda, K. Inoue, Y. Kibe, Y. Kishimoto, M. Koga, Y. Minekawa, [......], K. E. Downum, G. Gratta, K. Tolich, Y. Efremenko, O. Perevozchikov, H. J. Karwowski, D. M. Markoff, W. Tornow, K. M. Heeger, M. P. Decowski
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  ABSTRACT: The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet's interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2+/-1.0TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute TW to Earth's heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth's total heat flux. We therefore conclude that Earth's primordial heat supply has not yet been exhausted.
  Nature Geoscience 08/2011; 4:647-651. · 11.75 Impact Factor
• Article: Transverse beam spin asymmetries at backward angles in elastic electron-proton and quasielastic electron-deuteron scattering.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood, B Pasquini, M Vanderhaeghen
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  ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasielastic scattering on the deuteron, at backward angles (lab scattering angle of 108°) for Q² = 0.22 GeV²/c² and 0.63 GeV²/c² at beam energies of 362 and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single-photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (πN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasistatic deuterium approximation, and is also in agreement with theory.
  Physical Review Letters 07/2011; 107(2):022501. · 7.37 Impact Factor
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  Available from: Brian Fujikawa

  Article: Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector

  KamLAND Collaboration, S. Abe, K. Furuno, A. Gando, Y. Gando, K. Ichimura, H. Ikeda, K. Inoue, Y. Kibe, W. Kimura, [......], Y. Efremenko, Y. Kamyshkov, O. Perevozchikov, H. J. Karwowski, D. M. Markoff, W. Tornow, K. M. Heeger, F. Piquemal, J. -S. Ricol, M. P. Decowski
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  ABSTRACT: We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with Standard Solar Model predictions which include matter enhanced neutrino oscillation.
  06/2011;
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  Available from: Barbara Pasquini

  Article: Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasi-elastic Electron-Deuteron Scattering

  The Collaboration, D. Androić, D. S. Armstrong, J. Arvieux, S L Bailey, D. H. Beck, E. J. Beise, J. Benesch, F. Benmokhtar, L. Bimbot, [......], V. Tadevosyan, W T H Van Oers, M. Versteegen, E. Voutier, W. Vulcan, S.P. Wells, S. E. Williamson, S. A. Wood, B. Pasquini, M. Vanderhaeghen
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  ABSTRACT: We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasi-elastic scattering on the deuteron, at backward angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63 GeV^2/c^2 at beam energies of 362 MeV and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (piN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasi-static deuterium approximation, and is also in agreement with theory.
  03/2011;
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  Available from: R. Frascaria

  Article: The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

  Collaboration, D. Androic, D. S. Armstrong, J. Arvieux, R. Asaturyan, T. D. Averett, S L Bailey, G. Batigne, D. H. Beck, E. J. Beise, [......], E. Voutier, W. F. Vulcan, S.P. Wells, G. Warren, S. E. Williamson, R. J. Woo, S. A. Wood, C Yan, J Yun, V. Zeps
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  ABSTRACT: In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.
  03/2011;
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  Available from: ArXiv

  Article: Transverse Momentum Dependent Parton Distribution/Fragmentation Functions at an Electron-Ion Collider

  M. Anselmino, H Avakian, D. Boer, F. Bradamante, M. Burkardt, J P Chen, E. Cisbani, M. Contalbrigo, D Crabb, D Dutta, [......], V Sulkosky, Y Wang, B Xiao, Q Ye, Q-J. Ye, F Yuan, X Zhan, Y Zhang, W Zheng, J Zhou
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  ABSTRACT: We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimental studies of TMDs through measurements of single spin asymmetries (SSA) from semi-inclusive deep-inelastic scattering (SIDIS) processes with an EIC, and discuss the requirement of the detector for SIDIS measurements. The dynamics of parton correlations in the nucleon is further explored via a study of SSA in D (`D) production at large transverse momenta with the aim of accessing the unexplored tri-gluon correlation functions. The workshop participants identified the SSA measurements in SIDIS as a golden program to study TMDs in both the sea and valence quark regions and to study the role of gluons, with the Sivers asymmetry measurements as examples. Such measurements will lead to major advancement in our understanding of TMDs in the valence quark region, and more importantly also allow for the investigation of TMDs in the sea quark region along with a study of their evolution.
  01/2011;
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  Available from: Elizabeth Beise

  Article: Strange quark contributions to parity-violating asymmetries in the backward angle G0 electron scattering experiment.

  D Androić, D S Armstrong, J Arvieux, S L Bailey, D H Beck, E J Beise, J Benesch, F Benmokhtar, L Bimbot, J Birchall, [......], M Stutzman, R Suleiman, V Tadevosyan, W T H van Oers, M Versteegen, E Voutier, W Vulcan, S P Wells, S E Williamson, S A Wood
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  ABSTRACT: We have measured parity-violating asymmetries in elastic electron-proton and quasielastic electron-deuteron scattering at Q2=0.22 and 0.63 GeV2. They are sensitive to strange quark contributions to currents in the nucleon and the nucleon axial-vector current. The results indicate strange quark contributions of approximately < 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial-vector current at these four-momentum transfers.
  Physical Review Letters 01/2010; 104(1):012001. · 7.37 Impact Factor
• Article: Precision measurement of neutrino oscillation parameters with KamLAND.

  S Abe, T Ebihara, S Enomoto, K Furuno, Y Gando, K Ichimura, H Ikeda, K Inoue, Y Kibe, Y Kishimoto, [......], W Bugg, Y Efremenko, Y Kamyshkov, O Perevozchikov, H J Karwowski, D M Markoff, W Tornow, K M Heeger, F Piquemal, J-S Ricol
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  ABSTRACT: The KamLAND experiment has determined a precise value for the neutrino oscillation parameter Deltam21(2) and stringent constraints on theta12. The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to 2.44 x 10(32) proton yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor nu[over]e energy spectrum is now rejected at >5sigma. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at Deltam21(2)=7.58(-0.13)(+0.14)(stat) -0.15+0.15(syst) x 10(-5) eV2 and tan2theta12=0.56(-0.07)+0.10(stat) -0.06+0.10(syst). Local Deltachi2 minima at higher and lower Deltam21(2) are disfavored at >4sigma. Combining with solar neutrino data, we obtain Deltam21(2)=7.59(-0.21)+0.21 x 10(-5) eV2 and tan2theta12=0.47(-0.05)+0.06.
  Physical Review Letters 06/2008; 100(22):221803. · 7.37 Impact Factor
• Article: Transverse beam spin asymmetries in forward-angle elastic electron-proton scattering.

  D S Armstrong, J Arvieux, R Asaturyan, T Averett, S L Bailey, G Batigne, D H Beck, E J Beise, J Benesch, L Bimbot, [......], W T H van Oers, E Voutier, W Vulcan, G Warren, S P Wells, S E Williamson, S A Wood, C Yan, J Yun, V Zeps
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  ABSTRACT: We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic intermediate state contributions. A(n) provides a direct probe of the imaginary component of the 2gamma exchange amplitude, the complete description of which is important in the interpretation of data from precision electron-scattering experiments.
  Physical Review Letters 09/2007; 99(9):092301. · 7.37 Impact Factor
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  Available from: A.W.P Poon

  Article: Search for the invisible decay of neutrons with KamLAND.

  T Araki, S Enomoto, K Furuno, Y Gando, K Ichimura, H Ikeda, K Inoue, Y Kishimoto, M Koga, Y Koseki, [......], A Kozlov, Y Nakamura, H J Karwowski, D M Markoff, R M Rohm, W Tornow, R Wendell, M-J Chen, Y-F Wang, F Piquemal
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  ABSTRACT: The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the -shell energy level of (12)C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n--> 3v or nn--> 2v. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: tau(n--> inv) > 5.8 x 10(29) years and tau (nn--> inv) > 1.4 x 10(30) years at 90% C.L. These results represent an improvement of factors of approximately 3 and >10(4) and over previous experiments.
  Physical Review Letters 03/2006; 96(10):101802. · 7.37 Impact Factor
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  Available from: Elizabeth Beise

  Article: Strange-quark contributions to parity-violating asymmetries in the forward g0 electron-proton scattering experiment.

  D S Armstrong, J Arvieux, R Asaturyan, T Averett, S L Bailey, G Batigne, D H Beck, E J Beise, J Benesch, L Bimbot, [......], W van Oers, E Voutier, W Vulcan, G Warren, S P Wells, S E Williamson, S A Wood, C Yan, J Yun, V Zeps
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  ABSTRACT: We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.
  Physical Review Letters 09/2005; 95(9):092001. · 7.37 Impact Factor
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  Available from: Piotr Decowski

  Article: Precision measurement of the weak mixing angle in Møller scattering.

  P L Anthony, R G Arnold, C Arroyo, K Bega, J Biesiada, P E Bosted, G Bower, J Cahoon, R Carr, G D Cates, [......], P A Souder, Z M Szalata, J Turner, B Tweedie, A Vacheret, D Walz, T Weber, J Weisend, M Woods, I Younus
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  ABSTRACT: We report on a precision measurement of the parity-violating asymmetry in fixed target electron-electron (Møller) scattering: A(PV) = [-131 +/- 14(stat) +/- 10(syst)] x 10(-9), leading to the determination of the weak mixing angle sin2(thetaW(eff) = 0.2397 +/- 0.0010(stat) +/- 0.0008(syst), evaluated at Q2 = 0.026 GeV2. Combining this result with the measurements of sin2(thetaW(eff) at the Z0 pole, the running of the weak mixing angle is observed with over 6sigma significance. The measurement sets constraints on new physics effects at the TeV scale.
  Physical Review Letters 09/2005; 95(8):081601. · 7.37 Impact Factor
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  Available from: A.W.P Poon

  Article: Experimental investigation of geologically produced antineutrinos with KamLAND.

  T Araki, S Enomoto, K Furuno, Y Gando, K Ichimura, H Ikeda, K Inoue, Y Kishimoto, M Koga, Y Koseki, [......], Y Nakamura, H J Karwowski, D M Markoff, K Nakamura, R M Rohm, W Tornow, R Wendell, M-J Chen, Y-F Wang, F Piquemal
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  ABSTRACT: The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238U and 232Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.
  Nature 08/2005; 436(7050):499-503. · 36.28 Impact Factor
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  Available from: A.W.P Poon

  Article: Measurement of neutrino oscillation with KamLAND: evidence of spectral distortion.

  T Araki, K Eguchi, S Enomoto, K Furuno, K Ichimura, H Ikeda, K Inoue, K Ishihara, T Iwamoto, T Kawashima, [......], D M Markoff, J A Messimore, K Nakamura, R M Rohm, W Tornow, R Wendell, A R Young, M-J Chen, Y-F Wang, F Piquemal
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  ABSTRACT: We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 nu (e) candidate events with energies above 3.4 MeV compared to 365.2+/-23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8+/-7.3 expected background events, the statistical significance for reactor nu (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from nu (e) oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2). A global analysis of data from KamLAND and solar-neutrino experiments yields Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2) and tan((2)theta=0.40(+0.10)(-0.07), the most precise determination to date.
  Physical Review Letters 04/2005; 94(8):081801. · 7.37 Impact Factor