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Precision Measurement of Neutrino Oscillation Parameters with KamLAND

  • Author(s): ODonnell, Thomas Michael
  • Advisor(s): Freedman, Stuart J
  • et al.

This dissertation describes a measurement of the neutrino oscillation parameters $Delta m^2_{21}$, $theta_{12}$ and constraints on $theta_{13}$ based on a study of reactor antineutrinos at a baseline of $sim 180,$km with the KamLAND detector. The data presented here was collected between April 2002 and November 2009, and amounts to a total exposure of $2.64 \pm 0.07 times 10^{32}$ proton-years. For this exposure we expect $2140 \pm 74 (syst)$ antineutrino candidates from reactors, assuming standard model neutrino behavior, and $350 pm 88 (syst)$ candidates from background. The number observed is 1614. The ratio of background-subtracted candidates observed to expected is

$$frac{N_{Obs}-N_{Bkg}}{N_{Exp}} = 0.59 \pm 0.02 (stat)\pm 0.045 (syst)nonumber$$

which confirms reactor neutrino disappearance at greater than 5$sigma$ significance. Interpreting this deficit as being due to neutrino oscillation, the best-fit oscillation parameters from a three-flavor analysis are $Delta m^{2}_{21} = 7.60 ^{+0.20}_{-0.19} times 10^{-5} rm{eV^2}$, mbox{$theta_{12} = 32.5 \pm 2.9$ degrees} and $sin^{2}theta_{13} = 0.025 ^{+0.035}_{-0.035}$, the 95% confidence-level upper limit on $sin^{2}theta_{13}$ is mbox{$sin^{2}theta_{13}<0.083 $}. Assuming textit{CPT} invariance, a combined analysis of KamLAND and solar neutrino data yields best-fit values: $Delta m^{2}_{21} = 7.60 ^{+0.20}_{-0.20} times 10^{-5} rm{eV^2}$, $theta_{12} = 33.5 ^{+1.0}_{-1.1}$ degrees, and $sin^{2}theta_{13} = 0.013 pm {0.028}$ or $sin^{2}theta_{13}<0.06 $ at the 95% confidence level.

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