Observation of $e^{+}{e}^{-}\to \ddot{I}‰\ddot{I}{‡}_{c1,2}$ near $\sqrt{s}$ = 4.42 and 4.6 GeV

Abstract

Based on data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies $\sqrt{s}>$ 4.4 GeV, the processes $e^{+}{e}^{-}\to \ddot{I}‰\ddot{I}{‡}_{c1,2}$ are observed for the first time. With an integrated luminosity of $1074p{b}^{-1}$ near $\sqrt{s}=$ 4.42 GeV, a significant $\ddot{I}‰\ddot{I}{‡}_{c2}$ signal is found, and the cross section is measured to be $(20.9 \pm 3.2 \pm 2.5)\pb$. With $567p{b}^{-1}$ near $\sqrt{s}=$ 4.6 GeV, a clear $\ddot{I}‰\ddot{I}{‡}_{c1}$ signal is seen, and the cross section is measured to be $(9.5 \pm 2.1 \pm 1.3) \pb$, while evidence is found for an $\ddot{I}‰\ddot{I}{‡}_{c2}$ signal. The first errors are statistical and the second are systematic. Due to low luminosity or low cross section at other energies, no significant signals are observed. In the $\ddot{I}‰\ddot{I}{‡}_{c2}$ cross section, an enhancement is seen around $\sqrt{s}=$ 4.42 GeV. Fitting the cross section with a coherent sum of the $\ddot{I}ˆ(4415)$ Breit-Wigner function and a phase space term, the branching fraction $\mathcal{B}(\ddot{I}ˆ(4415)\to \ddot{I}‰\ddot{I}{‡}_{c2})$ is obtained to be of the order of $10^{-3}$.

7 pages, 3 figures