Neutrino Oscillation Parameters After High Statistics KamLAND Results

Abstract

We do a re-analysis to asses the impact of the results of the Borexino experiment and the recent 2.8 KTy KamLAND data on the solar neutrino oscillation parameters. The current Borexino results are found to have no impact on the allowed solar neutrino parameter space. The new KamLAND data causes a significant reduction of the allowed range of $\Delta m^2_{21}$, determining it with an unprecedented precision of 8.3% at 3$\sigma$. The precision of $\Delta m^2_{21}$ is controlled practically by the KamLAND data alone. Inclusion of new KamLAND results also improves the upper bound on $\sin^2\theta_{12}$, but the precision of this parameter continues to be controlled by the solar data. The third mixing angle is constrained to be $\sin^2\theta_{13} < 0.063$ at $3\sigma$ from a combined fit to the solar, KamLAND, atmospheric and CHOOZ results. We also address the issue of how much further reduction of allowed range of $\Delta m^2_{21}$ and $\sin^2\theta_{12}$ is possible with increased statistics from KamLAND. We find that there is a sharp reduction of the $3\sigma$ ``spread'' with enhanced statistics till about 10 KTy after which the spread tends to flatten out reaching to less than 4% with 15 KTy data. For $\sin^2\theta_{12}$ however, the spread is more than 25% even after 20 KTy exposure and assuming $\theta_{12} < \pi/4$, as dictated by the solar data. We show that with a KamLAND like reactor ``SPMIN'' experiment at a distance of $\sim$ 60 km, the spread of $\sin^2\theta_{12}$ could be reduced to about 5% at $3\sigma$ level while $\Delta m_{21}^2$ could be determined to within 4%, with just 3 KTy exposure.