Neutrino Oscillation Parameters After High Statistics KamLAND Results

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 ∆m21, determining it with an unprecedented precision of 8.3% at 3σ. The precision of ∆m21 is controlled practically by the KamLAND data alone. Inclusion of new KamLAND results also improves the upper bound on sin θ12, but the precision of this parameter continues to be controlled by the solar data. The third mixing angle is constrained to be sin θ13 < 0.063 at 3σ 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 ∆m21 and sin 2 θ12 is possible with increased statistics from KamLAND. We find that there is a sharp reduction of the 3σ “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 θ12 however, the spread is more than 25% even after 20 KTy exposure and assuming θ12 < π/4, as dictated by the solar data. We show that with a KamLAND like reactor “SPMIN” experiment at a distance of ∼ 60 km, the spread of sin θ12 could be reduced to about 5% at 3σ level while ∆m 2 21 could be determined to within 4%, with just 3 KTy exposure. Also at: INRNE, Bulgarian Academy of Sciences, Sofia, Bulgaria