A. N. Zhuravlev

Measurement of the τ lepton mass at the KEDR detector

A precise τ lepton mass measurement performed at the VEPP-4M collider with the KEDR detector is reported. The mass value is evaluated from the τ+τ− cross section behavior around the production threshold. The result based on 6.7 pb−1 of data is mτ = 1776.81−0.23+0.25 ± 0.15 MeV. Using 0.8 pb−1 of data collected at the ψ′ peak, we have also determined that ΓeeBττ(ψ′) = 9.0 ± 2.6 eV.

Measurement of the ratio of the leptonic widths

The ratio of the electron and muon widths of the

\Gamma_{ee}/\Gamma_{\mu\mu}

J/\psi

for the

meson has been measured using direct

J/\psi

J/\psi

meson

decays in the KEDR experiment at the VEPP-4M electron-positron collider. The result

Measurement of \Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-) and \Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)

\Gamma_{ee}(J/\psi)/\Gamma_{\mu\mu}(J/\psi)=1.0022\pm0.0044\pm0.0048\ (0.65\%)

Measurement of B(J/psi->eta_c gamma) at KEDR

is in good agreement with the lepton universality. The experience collected during this analysis will be used for a

Measurement of

J/\psi

\Gamma_{ee}\times\mathcal{B}_{\mu\mu}

lepton width determination with up to 1% accuracy.