V.V. Smaluk

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 main parameters of the ψ(2S) resonance

A high-precision determination of the main parameters of th eψ(2S ) resonance has been performed with the KEDR detector at the VEPP-4Me+e− collider in three scans of the ψ(2S )–ψ(3770) energy range. Fitting the energy dependence of the mu ltihadron cross section in the vicinity of theψ(2S ) we obtainedthe mass value M = 3686.114± 0.007± 0.011 +0.002 −0.012 MeV and the product of the electron partial width by the branchin g fraction into hadrons Γee × Bh = 2.233± 0.015± 0.037± 0.020 keV. The third error quoted is an estimate of the model dependence of the result due to assumptions on the interference e ffects in the cross section of the single-photon e+e− annihilation to hadrons explicitly considered in this work . Implicitly, the same assumptions were employed to obtain the charmonium leptonic width and th e absolute branching fractions in many experiments. Usingthe result presented and the world average values of the electron and hadron branchin g fractions, one obtains the electron partial width and the total width of the ψ(2S ): Γee = 2.282± 0.015± 0.038± 0.021 keV, Γ = 296± 2± 8± 3 keV. These results are consistent with and more than two times mor e precise than any of the previous experiments.

Measurement of ψ(3770) parameters

Abstract We report the final results of a study of the ψ ( 3770 ) meson using a data sample collected with the KEDR detector at the VEPP-4M electron–positron collider. The data analysis takes into account interference between the resonant and nonresonant D D ¯ production, where the latter is related to the nonresonant part of the energy-dependent form factor F D . The vector dominance approach and several empirical parameterizations have been tried for the nonresonant F D N R ( s ) . Our results for the mass and total width of ψ ( 3770 ) are M = 3779.2 − 1.7 + 1.8 − 0.7 + 0.5 − 0.3 + 0.3 MeV , Γ = 24.9 − 4.0 + 4.6 − 0.6 + 0.5 − 0.9 + 0.2 MeV , where the first, second and third uncertainties are statistical, systematic and model, respectively. For the electron partial width two possible solutions have been found: ( 1 ) Γ e e = 154 − 58 + 79 − 9 + 17 − 25 + 13 eV , ( 2 ) Γ e e = 414 − 80 + 72 − 26 + 24 − 10 + 90 eV . Our statistics are insufficient to prefer one solution to another. The Solution (2) mitigates the problem of non- D D ¯ decays but is disfavored by potential models. It is shown that taking into account the resonance–continuum interference in the near-threshold region affects resonance parameters, thus the results presented cannot be directly compared with the corresponding PDG values obtained ignoring this effect.

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

We present a study of the inclusive photon spectrum from 6.3 million J/ψ decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/ψ → ηcγ, ηc width and mass. Taking into account an asymmetric photon line shape we obtain: Mηc = (2978.1 ± 1.4 ± 2.0) MeV/c2, Γηc = (43.5 ± 5.4 ± 15.8) MeV,

Measurement of Γee(J/ψ) with KEDR detector

\mathcal{B}(J/\psi\to \eta_{{\rm c}}\gamma) = (2.59 \pm 0.16 \pm 0.31)\%

Measurement of Γee(J/ψ)⋅B(J/ψ→e+e−)Γee(J/ψ)⋅B(J/ψ→e+e−) and Γee(J/ψ)⋅B(J/ψ→μ+μ−)Γee(J/ψ)⋅B(J/ψ→μ+μ−)

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Measurement of Gamma(ee)(J/psi)*Beta(J/psi ---> e+ e-) and Gamma(ee)(J/psi)*Beta(J/psi ---> mu+ mu-)

A bstractThe product of the electronic width of the J/ψ meson and the branching fractions of its decay to hadrons and electrons has been measured using the KEDR detector at the VEPP-4M e+e− collider. The obtained values are ΓeeJ/ψ=5.550±0.056±0.089keV,ΓeeJ/ψ·ℬhadronsJ/ψ=4.884±0.048±0.078keV,ΓeeJ/ψ·ℬeeJ/ψ=0.3331±0.0066±0.0040keV.

New precise determination of the τ lepton mass at KEDR detector

\begin{array}{c}\hfill {\Gamma}_{ee}\left(J/\psi \right)=5.550\pm 0.056\pm 0.089\kern0.5em \mathrm{keV},\hfill \\ {}\hfill {\Gamma}_{ee}\left(J/\psi \right)\cdotp {\mathrm{\mathcal{B}}}_{\mathrm{hadrons}}\left(J/\psi \right)=4.884\pm 0.048\pm 0.078\kern0.5em \mathrm{keV},\hfill \\ {}\hfill {\Gamma}_{ee}\left(J/\psi \right)\cdotp {\mathrm{\mathcal{B}}}_{ee}\left(J/\psi \right)=0.3331\pm 0.0066\pm 0.0040\kern0.5em \mathrm{keV}.\hfill \end{array}