Measurement of the weak mixing angle at a Super Charm-Tau factory with data-driven monitoring of the average electron beam polarization

A method for measuring the average longitudinal polarization of the electron beam at an electron-positron collider operating near the J/ψ resonance is proposed. The method utilizes the differential cross-section of J/ψ→[Λ→pπ−][Λ→p¯π+] decay. It can be used to measure the average longitudinal polarization of electrons with the statistical precision better than 10⁻³ at a Super Charm-Tau factory operating at the luminosity of 10³⁵ cm⁻²s⁻¹. The method is discussed in the context of the weak mixing angle measurement in the same experiment.