Use ${{\mathit \nu}_{{e}}}{{\mathit e}}$ scattering rate
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 and a high-metalicity standard solar model. The electron neutrino survival probability for the pep solar neutrino is calculated to be $0.43$ $\pm0.11$.
References:
AGOSTINI
2018B
NAT 562 505
Comprehensive measurement of $pp$-chain solar neutrinos