The \(e^+e^- \to \eta\pi^+\pi^-\) cross section is measured at the SND detector in the \(\eta\) decay mode \(\eta\to 3\pi^0\). The analysis is based on the data sample with an integrated luminosity ...of 32.7 pb\(^{-1}\) collected at the VEPP-2000 \(e^+e^-\) collider in the center-of-mass energy range \(\sqrt{s}=1.075-2.000\) GeV. The data obtained in the \(\eta\to 3\pi^0\) decay mode are found to be in agreement with the previous SND measurements in the \(\eta\to \gamma\gamma\) mode. Therefore the measurements in the two modes are combined.
Using \(e^{+}e^{-}\) collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated ...luminosity of 300 pb^{-1}, a partial-wave analysis is performed for the process \(e^{+}e^{-} \to K^{+}K^{-}\pi^{0}\pi^{0}\). The total Born cross sections for the process \(e^{+}e^{-} \to K^{+}K^{-}\pi^{0}\pi^{0}\), as well as the Born cross sections f or the subprocesses \(e^{+}e^{-} \to \phi \pi^{0}\pi^{0}\), \(K^{+}(1460)K^{-}\), \(K^{+}_{1}(1400)K^{-}\), \(K^{+}_{1}(1270)K^{-}\) and \(K^{*+}(892)K^{*-}(892)\), are measured versus the center-of-mass energy. The corresponding results for \(e^{+}e^{-} \to K^{+}K^{-}\pi^{0}\pi^{0}\) and \(\phi \pi^{0}\pi^{0}\) are consistent with those of BaBar and have much improved precision.By analyzing the cross sections for the four subprocesses, \(K^{+}(1460)K^{-}\), \(K^{+}_{1}(1400)K^{-}\), \(K^{+ }_{1}(1270)K^{-}\) and \(K^{*+}K^{*-}\), a structure with mass \(M\) = (2126.5 \(\pm\) 16.8 \(\pm\) 12.4)~MeV/c^{2} and width \(\Gamma\) = (106.9 \(\pm\) 32.1 \(\pm\) 28.1)~MeV is observed with an overall statistical significance of 6.3 \(\sigma\), although with very limited significance in the subprocesses \(e^{+}e^{-} \to K^{+}_{1}(1270)K^{-}\) and \(K^{*+}(892)K^{*-}(892)\). The resonant parameters of the observed structure suggest it can be identified with the \(\phi(2170)\), thus the results provide valuable input to the internal nature of the \(\phi(2170)\).
Using the KEDR detector at the VEPP-4M \(e^+e^-\) collider, we have determined the values of \(R\) at thirteen points of the center-of-mass energy between 1.84 and 3.05 GeV. The achieved accuracy is ...about or better than \(3.9\%\) at most of the energy points with a systematic uncertainty less than \(2.4\%\).
The BEPC-II collider beam energy calibration system is discussed. The system is based on the Compton backscattering method. The expected precision of the electron and positron beam energy
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Using the KEDR detector at the VEPP-4M \(e^+e^-\) collider, we have measured the values of \(R_{\text{uds}}\) 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 \(3.3\%\) at most of energy points with a systematic uncertainty of about \(2.1\%\). At the moment it is the most accurate measurement of \(R(s)\) in this energy range.
Nucl. Phys. B (Proc. Suppl.) 225-227 (2012) 216 We report on the status of the Novosibirsk experiment on a precision
measurement of the ratio $R$ of the elastic $e^+ p$ and $e^- p$ scattering
cross ...sections. Such measurements determine the two-photon exchange effect in
elastic electron-proton scattering. The experiment is conducted at the VEPP-3
storage ring using a hydrogen internal gas target. The ratio $R$ is measured
with a beam energy of 1.6 GeV (electron/positron scattering angles are $\theta
= 55 \div 75^{\circ}$ and $\theta = 15 \div 25^{\circ}$) and 1 GeV ($\theta =
65 \div 105^{\circ}$). We briefly describe the experimental method, paying
special attention to the radiative corrections. Some preliminary results are
presented.
A precise comparison of the cross sections for the elastic scattering of electrons and positrons on protons was performed recently at the VEPP-3 storage ring in Novosibirsk, Russia. To provide the ...proposed accuracy, the energies of the electron and positron beams used during the experiment needed to be carefully maintained. This paper describes a special beam energy measurement system used in this experiment. This system is based on measuring the maximum energy of laser photons backscattered from electron and positron beams. It provides continuous beam energy measurements with a total relative uncertainty of less than \(4.4 \cdot 10^{-5}\).
A sensitivity of the VEPP-2000 \(e^+e^-\) collider in a search for the rare decay \(\eta \rightarrow e^+ e^-\) has been studied. The inverse reaction \(e^+ e^- \rightarrow \eta\) is proposed for this ...search. We have analyzed a data sample with an integrated luminosity of 108 nb\(^{-1}\) collected with the SND detector in the center-of-mass energy range 520-580 MeV and found no background events for the reaction \(e^+ e^- \rightarrow \eta\) in the decay mode \(\eta\to\pi^0\pi^0\pi^0\). In the absence of background, a sensitivity to \({\cal B}(\eta \rightarrow e^+ e^-)\) of \(10^{-6}\) can be reached during two weeks of VEPP-2000 operation. Such a sensitivity is better than the current upper limit on \({\cal B}(\eta \rightarrow e^+ e^-)\) by a factor of 2.3.
A search for the process \(e^+e^- \to \eta^\prime\) has been performed with the SND detector at the VEPP-2000 \(e^+e^-\) collider. The data were accumulated at the center-of-mass energy of ...\(957.78\pm 0.06\) MeV with an integrated luminosity of about 2.9 pb\(^{-1}\). For reconstruction of the \(\eta^\prime\) meson five decay chains have been used: \(\eta^{\prime}\to\eta\pi^+\pi^-\) followed by the \(\eta\) decays to \(\gamma\gamma\) and \(3\pi^0 \), and \(\eta^{\prime} \to \eta\pi^0\pi^0\) followed by the \(\eta\) decays to \(\pi^+\pi^-\pi^0\), \(\gamma\gamma\), and \(3\pi^0\). As a result, the upper limit has been set on the \(\eta^\prime\) electronic width: \(\Gamma_{\eta^{\prime}\to e^+e^-} < 0.0020\) eV at the 90\% confidence level.
The ratio of the elastic \(e^+ p\) to \(e^- p\) scattering cross sections has been measured precisely, allowing the determination of the two-photon exchange contribution to these processes. This ...neglected contribution is believed to be the cause of the discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. The experiment was performed at the VEPP-3 storage ring at beam energies of 1.6 and 1.0 GeV and at lepton scattering angles between \(15^\circ\) and \(105^\circ\). The data obtained show evidence of a significant two-photon exchange effect. The results are compared with several theoretical predictions.
