Resolving the Solar Neutrino Problem with KamLAND

We study how well KamLAND, the first terrestrial neutrino experiment capable of addressing the solar neutrino problem, will perform in ascertaining whether or not the large mixing angle MSW solution (with $10^{-5}<\Delta m_{21}^2< 10^{-3} eV^2$ and oscillation amplitude $sin^2 2 \theta_{12}>0.2$) is correct. We find that in a year of operation KamLAND will provide unequivocal evidence for or against this solution. Furthermore, its sensitivity to the three-neutrino oscillation parameters in this region is sufficiently acute as to determine $\Delta m_{21}^2$ to approximately $\pm 10$ % (for $sin^2 2 \theta_{12}>0.7$) and to fix $sin^2 2 \theta_{12}$ to within $\pm 0.1$ (at the $3\sigma$ level) with three years of accumulated data, independent of the value of $\theta_{13}$.