G.M. Tumaikin

Investigation of the φ-meson resonance by electron-positron colliding beams

Abstract Using the colliding beam machine, VEPP-2, the excitation curve of the o-meson resonance was investigated in the three main decay modes. The resonance parameters obtained are the width, the total cross-section and the branching ratios. Namely: Γ = (4.67 ± 0.42) Mev B ( K + K − ) = (54.0 ± 3,4) % σ o = (3.96 ± 0.35) μB B ( K o s K O L ) = (25.7 ±3,0) % B ( e + e − = (2,81 ± 0.25) × 10 −4 B ( π + π − π o ) = (20.3 ± 4,2) % In addition, the pion form factor at 2 E = 1020 MeV is obtained together with an upper limit for branching ratio of the φ-meson decay into a pion pair: z . sfnc ; F π z . sfnc ; 2 =2.92±1,2 B ( π + π −

High precision measurement of the Ψ- and Ψ′-meson masses

Abstract A high precision measurement of the Ψ- and Ψ′-resonance masses has been performed at the new storage ring VEPP-4. The resonance depolarization method has been used for the absolute calibration of the beam energy. Application of this technique allowed improvement of the accuracy of the Ψ- and Ψ′-mass measurements by a factor of more than ten. The following mass values have been obtained: m Ψ = 3096.93 ± 0.09 MeV, m Ψ ′ = 3686.00 ± 0.10 MeV; the mass difference is thus m Ψ ′ − m Ψ = 589.07 ± 0.13 MeV.

A high precision measurement of the ϒ, ϒ′ and ϒ″-meson masses

Abstract An experiment has been performed at the storage ring VEPP-4 using the MD-1 detector. The resonance depolarization method has been employed for the absolute calibration of the beam energy. This has allowed the accuracy of the mass measurement to be improved by a factor of ten. The following mass values of ϒ, ϒ′ and ϒ″ -mesons have been obtained: M ( ϒ )=9460.6±0.4 MeV, M ( ϒ ′)=10023.8±0.5 MeV, M ( ϒ ″)=10355.5±0.5 MeV.

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.

Large impact parameter cut-off in the process e+e−→e+e−γ

Abstract In investigating the e + e − → e + e − γ process the radiation probability is oberved to be substantially less than that calculated in the standard QED. The effect is due to the fact that the characteristic impact parameters in the process are much greater than the transverse sizes of the colliding beams. The Compton scattering γ-spectrum of the synchrotron radiation by a colliding beam is measured.

Pion form factor measurement by e+e− → π+π− in the energy range 2E from 0.78 up to 1.34 GeV

Abstract The cross section of the reaction e + e − → π + π − has been measured in the energy range 2 E from 0.78 up to 1.34 GeV. The obtained experimental values of the pion form factor exceed notably the ρ -meson tail.

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.

Absolute calibration of particle energy at VEPP-4M

We have started a new series of experiments on a precise measurement of J/Ψ-, Ψ′- mesons and τ-lepton masses at VEPP-4M collider with KEDR detector. Features of the method used for an absolute particle energy calibration based on the resonance depolarization are described.

An observation of the spin dependence of synchrotron radiation intensity

Abstract An experiment dealing with the observation of a change in the synchrotron radiation (SR) intensity during beam depolarization at the VEPP-4 storage ring is described. With a minute of measurement time, the magnitude of the effect exceeded ten statistical errors. The dependence of the sign of the effect on the sign of the magnetic field at the radiation point is demonstrated. The measured magnitude of the jump in the intensity is in agreement with the calculated spin-dependent contribution within a statistical error (equal to 7%). The suggested method is shown to be effectively applied to the observation of the transverse beam polarization in electron-positron storage rings.

Measurement of R uds and R between 3.12 and 3.72 GeV at the KEDR detector

Using the KEDR detector at the VEPP-4M e + e − e + e − collider, we have measured the values of R uds R uds and R at seven points of the center-of-mass energy between 3.12 and 3.72 GeV. The total achieved accuracy is about or better than 3.3% 3.3 % at most of energy points with a systematic uncertainty of about 2.1% 2.1 % . At the moment it is the most accurate measurement of R(s) R ( s ) in this energy range.