D.A. Maksimov

The KEDR detector

The KEDR detector is a universal magnetic detector designed for studying the c- and b-quarks and two-photon physics, and is employed at the VEPP-4M e + e − collider. A specific feature of the experiment is the measurement of absolute beam energy using two methods: the resonant depolarization and the faster but less precise Compton backscattering of laser photons. This allowed a large series of measurements to be performed, in which the accuracy of determination of such fundamental parameters of particles as mass and total and leptonic widths was improved.

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.