Confirmation of the $Y(4260)$ resonance production in initial state radiation

Using $13.3{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken in the ${\rm Y}(1S-4S)$ region with the CLEO III detector at the CESR collider, a search has been made for the new resonance $Y(4260)$ recently reported by the BABAR Collaboration. The production of $Y(4260)$ in initial state radiation (ISR), and its decay into ${\pi }^{+}{\pi }^{-}J/\psi$, are confirmed. A good quality fit to our data is obtained with a single resonance. We determine $M(Y(4260))=({4284}_{-16}^{+17}(\mathrm{stat})\pm 4(\mathrm{syst}))\mathrm{MeV}/c^2$, $\Gamma (Y(4260))=({73}_{-25}^{+39}(\mathrm{stat})\pm 5(\mathrm{syst}))\mathrm{MeV}/c^2$, and ${\Gamma }_{ee}(Y(4260))\times \mathcal{B}(Y(4260)\to {\pi }^{+}{\pi }^{-}J/\psi )=({8.9}_{-3.1}^{+3.9}(\mathrm{stat})\pm 1.8(\mathrm{syst}))\mathrm{eV}/c^2$.

Figure 1

Distributions of data events (points) for $M_{\mathrm{miss}}^2$, as defined in the text. The peaks centered at $M_{\mathrm{miss}}^2=0$ and bounded by the dashed lines correspond to the missing ISR photons. The shaded histograms show $\psi (2S)$ ISR signal Monte Carlo predictions normalized to the peak counts.

Figure 2

Event distributions after kinematic fitting for the invariant mass $M({\pi }^{+}{\pi }^{-}J/\psi )$, with $J/\psi \to e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$. Evidence for the production of $Y(4260)$ is present in both distributions.

Figure 3

The $M({\pi }^{+}{\pi }^{-}J/\psi )$ distribution for the sum of $J/\psi \to e^{+}{e}^{-}$ and $J/\psi \to {\mu }^{+}{\mu }^{-}$. The dotted line denotes the fitted background, and the solid curve denotes the fit with a single resonance. The semilog plot in the insert illustrates the $\psi (2S)$ excitation in the extended mass region.

Figure 4

Dipion mass distribution for data events (points). The shaded histogram is the Monte Carlo prediction for $M({\pi }^{+}{\pi }^{-})$ based on a $S$-wave phase space model. Neither the data nor the Monte Carlo distributions have been corrected for the experimental efficiency.