Measurement of $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)$ via Initial State Radiation at Belle

Abstract

We report measurement of the cross section of $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)$ between 4.0 and $5.5\mathrm{GeV}$, based on an analysis of initial state radiation events in a $980\mathrm{f}{\mathrm{b}}^{-1}$ data sample recorded with the Belle detector. The properties of the $Y(4360)$ and $Y(4660)$ states are determined. Fitting the mass spectrum of $\ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)$ with two coherent Breit-Wigner functions, we find two solutions with identical mass and width but different couplings to electron-positron pairs: $M_{Y(4360)}=(4347\pm 6\pm 3)\mathrm{MeV}/c^2$, $\hat{I}{“}_{Y(4360)}=(103\pm 9\pm 5)\mathrm{MeV}$, $M_{Y(4660)}=(4652\pm 10\pm 8)\mathrm{MeV}/c^2$, $\hat{I}{“}_{Y(4660)}=(68\pm 11\pm 1)\mathrm{MeV}$; and $\mathcal{B}[Y(4360)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)]\cdot \hat{I}{“}_{Y(4360)}^{e^{+}{e}^{-}}=(10.9\pm 0.6\pm 0.7)\mathrm{eV}$ and $\mathcal{B}[Y(4660)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)]\cdot \hat{I}{“}_{Y(4660)}^{e^{+}{e}^{-}}=(8.1\pm 1.1\pm 0.5)\mathrm{eV}$ for one solution; or $\mathcal{B}[Y(4360)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)]\cdot \hat{I}{“}_{Y(4360)}^{e^{+}{e}^{-}}=(9.2\pm 0.6\pm 0.6)\mathrm{eV}$ and $\mathcal{B}[Y(4660)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(2S)]\cdot \hat{I}{“}_{Y(4660)}^{e^{+}{e}^{-}}=(2.0\pm 0.3\pm 0.2)\mathrm{eV}$ for the other. Here, the first errors are statistical and the second systematic. Evidence for a charged charmoniumlike structure at $4.05\mathrm{GeV}/c^2$ is observed in the $\ddot{I}{€}^{\pm }\ddot{I}ˆ(2S)$ intermediate state in the $Y(4360)$ decays.

21 pages, 12 figures