$ ^7 Be$ Neutrino Signal Variation in KamLAND

Abstract

Large Mixing Angle (LMA) neutrino oscillation is the main solution for the long-standing Solar Neutrino Problem (SNP). Whether there is any subdominant effect accompanying the dominant LMA solution can not be ruled out at the moment, but will be settled by the forthcoming data from highly skilled real time experiments targeting essentially the low energy domain of solar neutrinos. Assuming a subdominant effect converting one of the active neutrinos into a sterile partner in the varying solar field with changing sunspot activity, we performed field-profile-independent predictions for $^7 Be$ neutrino signal variation, which might be tested in the KamLAND's future solar neutrino detection program. We found that after a substantial reduction of background and running of KamLAND solar mode through the sunspot maximum period (around 2010 - 2012), when the solar field at the resonance may vary from few $kG$ to $300~kG$, the subdominant time variation effect might be clearly visible (more than $5σ$) for $^7 Be$ neutrinos.