The process $e^+e^-\to\omega\eta\pi^0$ is studied in the energy range $1.45-2.00$ GeV using data with an integrated luminosity of 33 pb$^{-1}$ accumulated by the SND detector at the $e^+e^-$ collider VEPP-2000. The $e^+e^-\to\omega\eta\pi^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range $1.8-2.0$ GeV. The dominant intermediate state for the process $e^+e^- \to \omega\eta\pi^0$ is found to be $\omega a_0(980)$.
The energy interval, integrated luminosity ($L$), number of selected events ($N$), estimated number of background events ($N_{bkg}$), detection efficiency for $e^+e^-\to\omega\eta\pi^0\to 7\gamma$ events ($\epsilon$), radiative correction ($\delta+1$), and $e^+e^-\to\omega\eta\pi^0$ Born cross section ($\sigma$). The shown cross-section errors are statistical. The systematic error is 4.2%. The 90% confidence level upper limits are listed for the first two energy intervals.
In the study of the reaction $e^+e^-\to K_{S}K_{L}$ at the VEPP-2M $e^+e^-$ collider with the SND detector the nuclear interaction length of $K_{L}$ meson in NaI(Tl) has been measured. Its value is found to be 30--50 cm in the $K_{L}$ momentum range 0.11--0.48 GeV/$c$. The results are compared with the values used in the simulation programs GEANT4 and UNIMOD.
The energy interval ($\sqrt{s}$), integrated luminosity ($IL$), number of selected events ($N$), number of background events ($N_{\rm bkg}$), number of events with five or more photons ($N_{5\gamma}$, $N_{5\gamma,{\rm bkg}}$), and the measured $K_L$ nuclear interaction length in NaI(Tl) ($\lambda_{\rm int}$).
In the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider the cross section for the process $e^+e^-\to\eta\pi^+\pi^-$ has been measured in the center-of-mass energy range from 1.22 to 2.00 GeV. Obtained results are in agreement with previous measurements and have better accuracy. The energy dependence of the $e^+e^-\to\eta\pi^+\pi^-$ cross section has been fitted with the vector-meson dominance model. From this fit the product of the branching fractions $B(\rho(1450)\to\eta\pi^+\pi^-)B(\rho(1450)\to e^+e^-)$ has been extracted and compared with the same products for $\rho(1450)\to\omega\pi^0$ and $\rho(1450)\to\pi^+\pi^-$ decays. The obtained cross section data have been also used to test the conservation of vector current hypothesis.
The c.m. energy ($\sqrt{s}$), integrated luminosity ($L$), detection efficiency ($\varepsilon$), number of selected signal events ($N$), radiative-correction factor ($1 + \delta$), measured $e^+e^- \to \eta \pi^+\pi^-$ Born cross section ($\sigma_B$). For the number of events and cross section the statistical error is quoted. The systematic uncertainty on the cross section is 8.3% at $\sqrt{s}<1.45$ GeV, 5.0% at $1.45<\sqrt{s}<1.60$ GeV, and 7.8% at $\sqrt{s}>1.60$ GeV.
The process $e^+e^-\to n\bar{n}$ has been studied at the VEPP-2000 $e^+e^-$ collider with the SND detector in the energy range from threshold up to 2 GeV. As a result of the experiment, the $e^+e^-\to n\bar{n}$ cross section and effective neutron form factor have been measured.
The $e^+e^-\to n\bar{n}$ cross section ($\sigma_{n\bar{n}}$) and neutron effective form factor ($F_n$) measured in 2011. The quoted errors are statistical. The systematic error is 17$\%$ for the cross section and 9$\%$ for the form factor.
The $e^+e^-\to n\bar{n}$ cross section ($\sigma_{n\bar{n}}$) and neutron effective form factor ($F_n$) measured in 2012. The quoted errors are statistical. The systematic error is 17$\%$ for the cross section and 9$\%$ for the form factor. NOTE: corrected an apparent typo in paper for second-last data point (1990 $\to$ 1960) to make the numbers consistent with the plot in Figure 9.
The cross section for the process e+e- --> omega pi0 --> pi0 pi0 gamma has been measured in the energy range 1.05--2.00 GeV. The experiment has been performed at the e+e- collider VEPP-2000 with the SND detector. The measured e+e- --> omega pi0 cross section above 1.4 GeV is the most accurate to date. Below 1.4 GeV our data are in good agreement with the previous SND and CMD-2 measurements. Data on the e+e- --> omega pi0 cross section are well described by the VMD model with two excited rho-like states. From the measured cross section we have extracted the gamma^* --> omega pi0 transition form factor. It has been found that the VDM model cannot describe simultaneously our data and data obtained from the omega --> pi0 mu+ mu- decay. We have also tested CVC hypothesis comparing our results on the e+e- --> omega pi0 cross section with data on the tau- --> omega pi- nu_{tau} decay.
The c.m. energy(E) and measured Born cross section(SIG). For the cross section, the first error is statistical, the second is systematic.
The cross section of the process e+e-\to\mu+\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-\to\mu+\mu- were normalized to the integrated luminosity measured using e+e-\to e+e- and e+e-\to\gamma\gamma processes. The ratio of the measured cross section to the theoretically predicted value is 1.006\pm 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> = 134.1\pm 0.5 \pm 1.2 and this is in agreement with theoretical expectation.
The E+ E- --> MU+ MU- cross section obtained using the (GAMMA GAMMA) luminosity measurement.
The measured E+ E- --> E+ E- cross section in the electron angle 30 to 150 degrees.
The cross section for the process $e^+e^- \to K^+K^-$ was measured in the energy range $\sqrt{s}$ = 1.04--1.38 GeV in the SND experiment at VEPP-2M $e^+e^-$ collider. The measured cross section is described by the Vector Meson Dominance model with contributions from the light vector mesons $\rho$, $\omega$, $\phi$ and their lowest excitations. The mean statistical accuracy of the measurement is 4.4 %, and the systematic uncertainty is 5.2 %.
The measured cross section and charged kaon form factor.
We present a measurement of the $e^+e^-\to K_SK_L$ cross section in the energy range $\sqrt{s}=1.04 \div 1.38$ GeV. For the energy $\sqrt{s}\geq 1.2$ GeV the cross section exceeds vector meson dominance model predictions with only $\rho(770)$, $\omega(783)$, and $\phi(1020)$ mesons taken into account. Measured cross section agrees well with previous measurements.
The Born cross section for the process E+ E- --> KS KL.
In experiment with the SND detector at VEPP-2M $e^+e^-$ collider the $e^+e^-\to\eta\gamma$ cross section was measured in the energy range $E$=0.60--1.38 GeV with the integrated luminosity of 27.8 pb$^{-1}$. The measured cross section is well described by the vector meson dominance model with contributions from the $\rho(770)$, $\omega(783)$, $\phi(1020)$, $\rho^{\prime}(1465)$ resonances and agrees with results of previous measurements. The decay probabilities $\BR(\phi\to\eta\gamma)$, $\BR(\omega\to\eta\gamma)$ and $\BR(\rho\to\eta\gamma)$ were measured with the accuracies better than or comparable to the world averages.
Cross section from the ETA --> 3PI0 decay mode.
Cross section from the ETA --> PI+ PI- PI0 decay mode.
The reactions gamma gamma -> pi^+pi^-pi^+pi^- and gamma gamma -> pi^+pi^0pi^-pi^0 are studied with the L3 detector at LEP in a data sample collected at centre-of-mass energies from 161GeV to 209GeV with a total integrated luminosity of 698/pb. A spin-parity-helicity analysis of the rho^0 rho^0 and rho^+ rho^- systems for two-photon centre-of-mass energies between 1GeV and 3GeV shows the dominance of the spin-parity state 2+ with helicity 2. The contribution of 0+ and 0- spin-parity states is also observed, whereas contributions of 2- states and of a state with spin-parity 2+ and zero helicity are found to be negligible.
Cross section for 4PI and (RHO0 RHO0) production.
Cross section for 4PI and (RHO+ RHO-) production.
Spin parity analysis fits for RHO0 RHO0.
Exclusive rho^+ rho^- production in two-photon collisions involving a single highly-virtual photon is studied with data collected at LEP at centre-of-mass energies 89 GeV < \sqrt{s} < 209 GeV with a total integrated luminosity of 854.7 pb^-1. The cross section of the process gamma gamma^* -> rho^+ rho^- is determined as a function of the photon virtuality, Q^2, and the two-photon centre-of-mass energy, W_gg, in the kinematic region: 1.2 GeV^2 < Q^2 < 30 GeV^2 and 1.1 GeV < W_gg < 3 GeV. The \rho^+\rho^- production cross section is found to be of the same magnitude as the cross section of the process gamma gamma^* -> rho^0 rho^0, measured in the same kinematic region by L3, and to have similar W_gg and Q^2 dependences.
Cross sections for the reaction E+ E- --> E+ E- RHO+ RHO-. The differentialcross sections are corrected to the centre of each bin.
Cross sections for the two photon production of RHO+ RHO-.
Differential cross section for the process E+ E- --> E+ E- (RHO+ PI- PI0 + RHO+ RHO- PI0 PI0) corrected to bin centre.
The cross section of the process $e^+e^-\to \pi^+\pi^-\pi^0$ was measured in the Spherical Neutral Detector experiment at the VEPP-2M collider in the energy region $\sqrt[]{s} = 980 \div 1380$ MeV. The measured cross section, together with the $e^+e^-\to \pi^+\pi^-\pi^0$ and $\omega\pi^+\pi^-$ cross sections obtained in other experiments, was analyzed in the framework of the generalized vector meson dominance model. It was found that the experimental data can be described by a sum of $\omega$, $\phi$ mesons and two $\omega^\prime$ and $\omega^{\prime\prime}$ resonances contributions, with masses $m_{\omega^\prime}\sim 1490$,$m_{\omega^{\prime\prime}}\sim 1790$ MeV and widths $\Gamma_{\omega^\prime}\sim 1210$, $\Gamma_{\omega^{\prime\prime}}\sim 560$ MeV. The analysis of the $\pi^+\pi^-$ invariant mass spectra in the energy region $\sqrt[]{s}$ from 1100 to 1380 MeV has shown that for their descriptionone should take into account the $e^+e^-\to\omega\pi^0\to\pi^+\pi^-\pi^0$ mechanism also. The phase between the amplitudes corresponding to the $e^+e^-\to\omega\pi$ and $e^+e^-\to\rho\pi$ intermediate states was measured for the first time. The value of the phase is close to zero and depends on energy.
The measured E+ E- --> PI+ PI- PI0 cross section.
The cross section of the $e^+e^-\to\omega\pi^0\to\pi^0\pi^0\gamma$ reaction was measured by the SND detector at VEPP-2M $e^+e^-$ collider in the energy range from threshold up to 1.4 GeV. Results of the cross section fitting by the sum of $\rho$, $\rho^{\prime}$ and $\rho^{\prime\prime}$ contributions are presented.
Only statistical errors are presented.
The processes$e^+e^-\rightarrow\eta\gamma, \pi^0\gamma\rightarrow 3\gamma$were studied in the SND experiment at the VEPP-2M collider in the energy region of the
Results of energy scan of the cross section.
Cross sections for PHI production and decay into the two states from a fit to the data at the peak.
In the experiment with the SND detector at VEPP-2M e^+e^- collider the process $e^+e^-\to\pi^+\pi^-\pi^0$ was studied in the energy range 2E_0 from 1.04 to 1.38 GeV. A broad peak was observed with the visible mass $M_{vis}=1220\pm 20$ MeV and cross section in the maximum $\sigma_0\simeq 4$ nb. The peak can be interpreted as a $\omega$-like resonance $\omega (1200)$.
The total cross section for E+ E- --> PI+ PI- PI0 after correction for efficiency and radiative effects.
Results of the SND experiment at the VEPP-2M e+ e- collider on the QED processes e+ e- --> e+ e- gamma and e+ e- --> e+ e- gamma gamma with production at large angles are presented. Energy and angular distributions of the final particles were studied. No deviations from QED with an accuracy of 3.8% for the first process and 10.3% for the second were found.
No statistical errors are given. 3.8 PCT is the total systematic error.
No statistical errors are given. 5.8 PCT is the total systematic error.
The $e^+e^- \to \omega \pi^0 \to \pi^0 \pi^0 \gamma$ process was investigated in the SND experiment at the VEPP-2M collider. A narrow energy interval near the $\phi$-meson was scanned. The observed cross-section reveals, at the level of three standard deviation, the interference effect caused by $\phi \to \pi^0\pi^0\gamma$ decay. The cross-section parameters, as well as the real and imaginary parts of the $\phi$-meson related amplitude, were measured.
Only statistical errors are presented. Cross section times branching ratio.
Cross section corrected for the branching ratio OMEGA --> PI0 GAMMA, at the PHI meson. In the range 984 to 1060 MeV the E+ E- --> OMEGA PI0 cross section can be approximated as (7.5 +- 0.9) + (0.06 +- 0.03) (SQRT(S)-M(PHI)) NB where M(PHI) = 1019.4 MeV and S is in MeV**2.
Exclusive differential cross sections of virtual bremsstrahlung in proton-proton scattering below the pion-production threshold have been measured for the first time. The total cross section integrated over photon invariant masses of 15 to 80MeV/c2 and integrated over the acceptance of the detector is 3.2±0.1±0.5pb. The data are compared to a low-energy calculation and a fully relativistic microscopic model, which predict a virtual bremsstrahlung cross section of 3.4 and 5.9 pb, respectively. Over the entire experimentally covered phase space, the low-energy calculation gives a better description of the data than the microscopic model.
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Short overview of experiments with SND detector at VEPP-2M e^+e^- collider in the energy range 2E = 400 - 1400 MeV and preliminary results of data analysis are presented.
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The paper describes experiments with the SND detector at VEPP-2M collider, carried out during the period from October 1995 until June 1997. The total integrated luminosity of 6.4 pb^{-1} was collected in the energy range 2E=0.4-1.4 GeV (MHAD97 experiment), corresponding to 4*10^5 mu^+ mu^- pairs produced. Preliminary results of the 1996 phi-meson experiment (FI96) are presented. The total number of phi-mesons produced is 4*10^6. New data on rare decays of phi and eta (550) mesons, in particular B(phi -> eta gamma) = (1.30+-0.06+-0.07)%, B(phi -> pi^0 pi^0 gamma) = (1.1+-0.2)*10^{-4}, (M_{pi^0 pi^0} > 800 MeV), B(phi -> f^0 gamma) = (4.7+-1.0)*10^{-4}, B(phi -> eta pi^0 gamma) = (1.3+-0.5)*10^{-4}, B(phi -> eta' gamma) < 1.7*10^{-4}, B(phi -> 2 pi^0 ) < 6*10^{-4} were obtained.
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Measurements have been made of the polarization of the recoil proton in the process γ p → π o p for photon energies of 850 - 1250 MeV and centre-of-mass angles of 80° - 125°. The results, which are to a typical accuracy of ±0.09, show a marked disagreement with previous phenomenological analyses above 1000 MeV.
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