sin²θ_W estimate and neutrino electromagnetic properties from low-energy solar data

We report new values of weak-mixing angle (${\sin }^2{\theta }_W$), neutrino effective magnetic moment (${\mu }_{\nu }^{eff}$) and the charge radii $\left(⟨r_{{\nu }_{\alpha }}^2⟩\right)$ using the lowest energy (to-date) solar neutrino data of pp, ⁷Be and pep spectra from phase I and phase II runs of Borexino experiment. The best-fit values obtained are ${\sin }^2{\theta }_W=0.235\pm 0.019$ at 1σ with a precision comparable to that of the combined reactor and accelerator very short-baseline experiments and ${\mu }_{\nu }^{eff}⩽8.7\times {10}^{-12}{\mu }_B$ at 90% C.L. with a factor of 3 improvement over the previous bounds. This leads to the improvement of constraints on all the related magnetic moment matrix elements for the Majorana-type and Dirac-type neutrinos in mass basis and also stronger bounds on the magnetic moment flavor states. The bounds on the neutrino charge radii obtained are $0.82\times {10}^{-32}$ cm² $⩽⟨r_{{\nu }_e}^2⟩⩽1.27\times {10}^{-32}$ cm² and $-9\times {10}^{-32}$ cm² $⩽⟨r_{{\nu }_{\mu },{\nu }_{\tau }}^2⟩⩽3.1\times {10}^{-31}$ cm² at 90% C.L. (paper)