Super-Kamiokande-IV data taking began in September of 2008 , and with upgraded electronics and improvements to water system dynamics , calibration and analysis techniques , a clear solar neutrino signal could be extracted at recoil electron kinetic energies as low as 3.5 MeV .
The SK-IV extracted solar neutrino flux between 3.5 and 19.5 MeV is found to be ( 2.36 \pm 0.02 ( stat . ) \pm 0.04 ( syst . ) ) \times 10 ^ { 6 } / ( cm ^ { 2 } sec ) .
The SK combined recoil electron energy spectrum favors distortions predicted by standard neutrino flavour oscillation parameters over a flat suppression at 1 \sigma level .
A maximum likelihood fit to the amplitude of the expected solar zenith angle variation of the elastic neutrino-electron scattering rate in SK , results in a day/night asymmetry of -3.2 \pm 1.1 ( stat . ) \pm 0.5 ( syst . ) \% .
The 2.7 \sigma significance of non-zero asymmetry is the first indication of the regeneration of electron type solar neutrinos as they travel through Earth ’ s matter .
A fit to all solar neutrino data and KamLAND yields \sin ^ { 2 } \theta _ { 12 } = 0.304 \pm 0.013 , \sin ^ { 2 } \theta _ { 13 } = 0.031 ^ { +0.017 } _ { -0.015 } and \Delta m ^ { 2 } _ { 21 } = 7.45 ^ { +0.20 } _ { -0.19 } \times 10 ^ { -5 } { eV } ^ { 2 } .