KamLAND Bounds on Solar Antineutrinos and neutrino transition magnetic moments

We investigate the possibility of detecting solar antineutrinos with the KamLAND experiment. These antineutrinos are predicted by spin-flavor oscillations at a significant rate even if this mechanism is not the leading solution to the SNP. The recent evidence from SNO shows that the solar neutrino flux arriving on earth could contain a residual component including sterile neutrinos and/or the antineutrinos of the active flavors. KamLAND is sensitive to antineutrinos originated from solar B neutrinos. From KamLAND negative results after 145 days of data taking, we obtain model independent limits on the total flux of solar antineutrinos Φ(B) < 1.1−3.5×104 cm s, more than one order of magnitude smaller than existing limits, and on their appearance probability P < 0.15% (95% CL). Assuming a concrete model for antineutrino production by spin-flavor precession, this upper bound implies an upper limit on the product of the intrinsic neutrino magnetic moment and the value of the solar magnetic field μB < 2.3 × 10 MeV 95% CL (for LMA (∆m, tan θ) values). Limits on neutrino transition moments are also obtained. For realistic values of other astrophysical solar parameters these upper limits would imply that the neutrino magnetic moment is constrained to be, in the most conservative case, μ≤3.9 × 10 μB (95% CL) for a relatively small field B = 50 kG. For higher values of the magnetic field we obtain: μ≤9.0 × 10 μB for field B = 200 kG and μ≤2.0 × 10 μB for field B = 1000 kG at the same statistical significance.