New Measurement Of ?₁₃ Via Neutron Capture On Hydrogen At Daya Bay

Neutrinos are fundamental constituents of the Standard Model of particle physics.They are some of the most abundant particles in the universe,are extremely light,have no electric charge,and their identities oscillate among three 'flavors'.The amplitudes of these oscillations are characterized with the three angles ?12,?23,and ?13.The accurate determination of ?13 is important for tests of oscillation theories,but is also key in searches at particle accelerators for leptonic CP violation,which may answer the basic question of why there is more matter than antimatter in the universe.This thesis presents a new independent measurement of oscillation amplitude sin22?13 at the Daya Bay Reactor Neutrino Experiment.Six nuclear reactors produced roughly 3×1021 electron antineutrinos (?)e every second.Eight 40-ton liquid scintillator detectors were used to identify (?)e via inverse ?-decays with the emitted neutron captured by hydrogen.A 5.0%deficit was observed in the number of (?)e measured farther from the reactors relative to nearer the reactors,indicating the fraction of (?)e that oscillated to a different flavor.The analytical techniques developed for this analysis may be useful to forthcoming neutrino experiments that will also use neutron captures on hydrogen.Furthermore,by combining with a measurement of sin22?13 using neutron captures on gadolinium,the most accurate result is obtained.Achievements in this thesis include:1.Using 621 days of data,780000 hydrogen-neutron captures were selected as ve.Backgrounds were analyzed,including random coincidences,gLi/8He ?-n decays,and spallation neutrons,and subtracted from the number of (?)e candidates.Comparing the resulting number of (?)e in the near and far detectors within the three-neutrino-oscillation framework yielded sin22?13 = 0.071±0.011.2.Correlations between the hydrogen-and gadolinium-capture measurements were studied,revealing that the most significant correlation is in the delayed event energy selection.A combination of the measurements produced the most precise result:sin2 2?13 = 0.082 ± 0.004.3.A generic energy response model of scintillation detectors was developed.It provides a thorough understanding of partial energy deposition,nonuniformity,nonlinearity,and their uncertainties and interrelations,for any scintillation-based detector.This understanding was applied to Daya Bay analyses and led to improved detector-related systematic uncertainties,which comprise the largest component of systematic uncertainty.