Measurement of the 8B solar neutrino flux with the KamLAND liquid scintillator detector

We report a measurement of the neutrino-electron elastic scattering rate from [superscript 8]B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5-MeV analysis threshold is 1.49 ± 0.14(stat) ± 0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a [superscript 8]B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77 ± 0.26(stat) ± 0.32(syst) ×10[superscript 6] cm[superscript −2]s[superscript −1]. The analysis threshold is driven by [superscript 208]Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic [superscript 11]Be. The measured rate is consistent with existing measurements and with standard solar model predictions which include matter-enhanced neutrino oscillation.United States. Dept. of Energy (Grant No. DE-FG03-00ER41138)United States. Dept. of Energy (Grant No. No. DE-AC02-05CH11231)United States. Dept. of Energy (Grant No. No. DE-FG02-01ER41166)Japan. Ministry of Education, Culture, Sports, Science and Technology (World Premier International Research Center Initiative (WPI Initiative))United States. Dept. of EnergyJapan. Ministry of Education, Culture, Sports, Science and Technology (Grant-in-Aid for Specially Promoted Research under Grant No. 16002002