Thomas O'Donnell
LBNL
Abstract:
KamLAND is a one kiloton liquid scintillator detector which studies neutrino oscillation with reactor-antineutrinos at an average baseline of
180km. The experiment was the first to report reactor-antinuetrinodisappearance consistent with the neutrino mass splitting favored by the LMA-MSW
solution to the Solar Neutrino Problem. Furthermore, KamLAND observed distortion of the reactor spectrum -- the
fingerprint of mass-driven flavor oscillation -- and is uniquely
sentitive to the mass splitting $\Delta m^{2}_{21}$.
In this talk I will describe the experiment and present the results of the most
recent data set which amounts to a total exposure of $3.49 \times 10^{32}$
proton-years and includes data collected with more favorable
background conditions achieved by a detector radiopurity upgrade.
Under the assumption of CPT invariance, a three-flavor analysis
combining KamLAND and solar data yields best-fit values of the oscillation
parameters: $\Delta m^{2}_{21} = 7.50^{+0.19}_{-0.20} \times 10^{-5} \rm{eV}^{2}$,
$\tan^{2} \theta_{12} = 0.452^{+0.035}_{-0.033}$, and weak constraints
on $\theta_{13}$.
Finally, as the current phase of data taking draws to an end, I will briefly describe KamLAND-Zen
--- a plan to repurpose the detector to search for neutrino-less double beta decay of $^{136}$Xe.