Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Measurement of the $e^+e^-\toπ^+π^-π^0$ cross section in the energy region from 0.56 to 1.1 GeV with the SND detector

SND Collaboration, M. N. Achasov, A. E. Alizzi, A. Yu. Barnyakov, K. I. Beloborodov, A. V. Berdyugin, D. E. Berkaev, A. G. Bogdanchikov, A. A. Botov, V. S. Denisov, T. V. Dimova, V. P. Druzhinin, R. A. Efremov, E. A. Eminov, L. B. Fomin, L. V. Kardapoltsev, A. A. Kattsin, A. G. Kharlamov, I. A. Koop, A. A. Korol, D. P. Kovrizhin, A. S. Kupich, A. P. Kryukov, N. A. Melnikova, N. Yu. Muchnoi, A. E. Obrazovsky, A. A. Oorzhak, I. V. Ovtin, E. V. Pakhtusova, E. A. Perevedentsev, I. A. Polomoshnov, K. V. Pugachev, Yu. A. Rogovsky, V. A. Romanov, S. I. Serednyakov, Yu. M. Shatunov, D. A. Shtol, Z. K. Silagadze, K. D. Sungurov, M. V. Timoshenko, I. K. Surin, Yu. V. Usov, I. M. Zemlyansky, V. N. Zhabin, Yu. M. Zharinov, V. V. Zhulanov, P. V. Zhulanova

Abstract

The precise measurement of the $e^+e^-\toπ^+π^-π^0$ cross section is performed in the center-of-mass energy range $E = 560$--1100 MeV using a data sample of 66 pb$^{-1}$ collected in the experiment with the SND detector at the VEPP-2000 $e^+e^-$ collider. The systematic uncertainty of the cross section measurement is 0.9\% at the maximum of the $ω$ resonance and 1.2\% at the maximum of the $φ$ resonance. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the $e^+e^-\toπ^+π^-π^0$ cross section measured by SND from 0.62 to 1.975 GeV is $(42.96\pm0.06\pm 0.45)\times 10^{-10}$. From the fit to the cross section data with the vector meson dominance model, the parameters of the $ω$, $ρ$, and $φ$ resonances are obtained. The obtained values of ${\cal B}(ω\to e^+e^-) {\cal B}(ω\to 3π)$, mass and width of the $ω$ meson, and ${\cal B}(ρ\to 3π)$ have accuracy better than the current world average values.

Measurement of the $e^+e^-\toπ^+π^-π^0$ cross section in the energy region from 0.56 to 1.1 GeV with the SND detector

Abstract

The precise measurement of the cross section is performed in the center-of-mass energy range --1100 MeV using a data sample of 66 pb collected in the experiment with the SND detector at the VEPP-2000 collider. The systematic uncertainty of the cross section measurement is 0.9\% at the maximum of the resonance and 1.2\% at the maximum of the resonance. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the cross section measured by SND from 0.62 to 1.975 GeV is . From the fit to the cross section data with the vector meson dominance model, the parameters of the , , and resonances are obtained. The obtained values of , mass and width of the meson, and have accuracy better than the current world average values.
Paper Structure (10 sections, 13 equations, 18 figures, 7 tables)

This paper contains 10 sections, 13 equations, 18 figures, 7 tables.

Table of Contents

  1. Introduction
  2. SND detector
  3. Selection of $e^+e^-\to\pi^+\pi^-\pi^0$ events
  4. Fitting the $M_{\gamma\gamma}$ distribution
  5. Background distribution
  6. Systematic uncertainty in $N_{3\pi}$
  7. Detection efficiency
  8. Fitting the measured cross section
  9. Comparison with previous measurements
  10. Conclusion

Figures (18)

  • Figure 1: SND detector, section along the beams: (1) beam pipe, (2) tracking system, (3) aerogel Cherenkov counters, (4) NaI (Tl) crystals, (5) vacuum phototriodes, (6) iron absorber, (7) proportional tubes, (8) iron absorber, (9) scintillation counters, (10) VEPP-2000 focusing solenoids.
  • Figure 2: The Born (solid curve) and visible (dashed curve) cross sections for the process $e^+e^-\to\pi^+\pi^-\pi^0$ in the energy region under study. The vertical lines separate five intervals in which different event selection conditions are used.
  • Figure 3: Left panel: The $\chi^2_{3\pi}$ distributing for data (point with error bars) and simulated events at $E=782.76$ MeV. The solid histogram is a sum of simulated signal and background distributions. The filled histogram represents background contribution. The dashed histogram is the background distribution multiplied by a factor of 25. Right panel: The $\Delta\varphi$ distribution for data events at $E=719.93$ MeV (solid histogram). The dotted histogram represents the signal simulation. The arrows indicate the selection condition.
  • Figure 4: Left panel: The distribution of the open angle between charged pions for simulated signal (solid histogram), $\pi^+\pi^-(\gamma)$ (dashed histogram), and $e^+e^-(\gamma\gamma)$ (dotted histogram) events at $E=719.93$ MeV. The arrow indicates the condition $\psi<140^\circ$. Right panel: The $E_{\rm EMC}/E$ distribution for data events at $E=679.78$ MeV (solid histogram). The dotted histogram represents the signal simulation. The arrow indicates the selection condition.
  • Figure 5: Left panel: The $M_{\gamma\gamma}$ spectrum for data events at $E=719.93$ MeV after applying the selection criteria for energy interval I (solid), II (dashed), III (dotted), and IV (dash-dotted). Right panel: The distribution of the open angle between charged pions for data (solid histogram), simulated signal (dashed histogram), and $K_S K_L$ (dotted histogram) events at $E=1019.1$ MeV, selected with the condition $\chi^2_{3\pi}<30$. The arrow indicates the condition $\psi<140^\circ$.
  • ...and 13 more figures