1AGOSTINI 2018B obtained this result from the measured ${{\mathit \nu}_{{{e}}}}{{\mathit e}}$ elastic scattering rate over the period between December 2011 and May 2016, assuming the MSW-LMA oscillation parameters derived by ESTEBAN 2017. Assuming a high-metalicity standard solar model, the electron neutrino survival probability for the ${{\mathit p}}{{\mathit p}}$ solar neutrino is calculated to be $0.57$ $\pm0.09$.
References:
AGOSTINI
2018B
NAT 562 505
Comprehensive measurement of $pp$-chain solar neutrinos