Measurement of the $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ process cross section with the SND detector at the VEPP-2000 collider in the energy region $0.525<\sqrt{s}<0.883$ GeV

Abstract

The cross section of the process $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 $e^{+}{e}^{-}$ collider VEPP-2000 in the energy region $525<\sqrt[]{s}<883$ MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb${}^{-1}$. The systematic uncertainty of the cross section determination is 0.8 % at $\sqrt{s}>0.600$ GeV. The $\ddot{I}$ meson parameters are obtained as $m_{\ddot{I}}=775.3\pm 0.5\pm 0.6$ MeV, $\hat{I}{“}_{\ddot{I}}=145.6\pm 0.6\pm 0.8$ MeV, $B_{\ddot{I}\to e^{+}{e}^{-}}\times B_{\ddot{I}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}}=(4.89\pm 0.02\pm 0.04)\times 10^{-5}$, and the parameters of the $e^{+}{e}^{-}\to \ddot{I}‰\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ process, suppressed by $G$-parity, as $B_{\ddot{I}‰\to e^{+}{e}^{-}}\times B_{\ddot{I}‰\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}}=(1.32\pm 0.06\pm 0.02)\times 10^{-6}$ and $\ddot{I}{•}_{\ddot{I}\ddot{I}‰}=110.7\pm 1.5\pm 1.0$ degrees.