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Register a new userSearch for Lepton Flavor Violation Process e^+e^- to emu in the Energy Region sqrt{s}=984 -- 1060 MeV and phito emu Decay
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The search for lepton-flavor-violation process e^+e^-to emu in the energy region sqrt{s}=984 - 1060 MeV with SND detector at VEPP-2M e^+e^- collider is reported. The model independent 90% CL upper limits on the e^+e^-to emu cross section, sigma_{emu} < 11 pb, as well as on the corresponding phito emu branching fraction, B(phito emu) < 2 times 10^{-6}, for the final particles polar angles 55^circ<theta<125^circ, were obtained.
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We search for the lepton-flavor-violating decay of the $J/psi$ into an electron and a muon using $(225.3pm2.8)times 10^{6}$ $J/psi$ events collected with the BESIII detector at the BEPCII collider. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of $mathcal{B}(J/psi to emu)< 1.5 times 10^{-7}$ (90% C.L.) is obtained.
The cross section of the process e^+e^-to pi^+pi^- was measured in the SND experiment at the VEPP-2M collider in the energy region 400<sqrt[]{s}<1000 MeV. This measurement was based on about 12.4 times 10^6 selected collinear events, which include 7.4times 10^6 e^+e^-to e^+e^-, 4.5times 10^6 e^+e^-topi^+pi^- and 0.5times 10^6 e^+e^-tomu^+mu^- selected events. The systematic uncertainty of the cross section determination is 1.3 %. The rho-meson parameters were determined: m_rho=774.9pm 0.4pm 0.5 MeV, Gamma_rho=146.5pm 0.8pm 1.5 MeV, sigma(rhotopi^+pi^-)=1220pm 7pm 16 nb as well as the parameters of the G-parity suppressed decay omegatopi^+pi^-: sigma(omegatopi^+pi^-)=29.9pm 1.4pm 1.0 nb and phi_{rhoomega} = 113.5pm 1.3pm 1.7 degree.
The cross section of the process e+e-tomu+mu- was measured in the SND experiment at the VEPP-2M e+e- collider in the energy region sqrt{s}=980, 1040 -- 1380 MeV. The event numbers of the process e+e-tomu+mu- were normalized to the integrated luminosity measured using e+e-to e+e- and e+e-togammagamma processes. The ratio of the measured cross section to the theoretically predicted value is 1.006pm 0.007 pm 0.016 and 1.005 pm 0.007 pm 0.018 in the first and second case respectively. Using results of the measurements, the electromagnetic running coupling constant alpha in the energy region sqrt{s}=1040 -- 1380 MeV was obtained <1/alpha> = 134.1pm 0.5 pm 1.2 and this is in agreement with theoretical expectation.
We report the results of a search for the $X(1835)$ state in the process $e^+e^-to J/psi+X(1835)$ using a data sample of 672 fb$^{-1}$ collected with the Belle detector at and near the $Upsilon(4S)$ resonance at the KEKB asymmetric-energy $e^+e^-$ collider. No significant evidence is found for this process, and an upper limit is set on its cross section times the branching fraction: $sigma_{rm Born}(e^+e^- to J/psi X(1835)) cdot$ {${cal B}(X(1835)to ge 3$ charged tracks)} $< 1.3 {rm fb}$ at 90% confidence level.
The cross section of the process $e^+e^-to pi^+pi^-pi^0$ was measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2M collider in the energy region $sqrt[]{s}$ below 980 MeV. This measurement was based on about $1.2 times 10^6$ selected events. The obtained cross section was analyzed together with the SND and DM2 data in the energy region $sqrt[]{s}$ up to 2 GeV. The $omega$-meson parameters: $m_omega=782.79pm 0.08pm 0.09$ MeV, $Gamma_omega=8.68pm 0.04pm 0.15$ MeV and $sigma(omegato 3pi)=1615pm 9pm 57$ nb were obtained. It was found that the experimental data cannot be described by a sum of only $omega$, $phi$, $omega^prime$ and $omega^{primeprime}$ resonances contributions. This can be interpreted as a manifestation of $rhoto 3pi$ decay, suppressed by $G$-parity, with relative probability $B(rhoto 3pi) = (1.01pm^{0.54}_{0.36}pm 0.034) times 10^{-4}$.
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