Precise Measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ Cross Section at Center-of-Mass Energies from 3.77 to 4.60 GeV

The cross section for the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using $9{\mathrm{fb}}^{-1}$ of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of $(4222.0\pm 3.1\pm 1.4)\mathrm{MeV}/c^2$ and a width of $(44.1\pm 4.3\pm 2.0)\mathrm{MeV}$, while the second one has a mass of $(4320.0\pm 10.4\pm 7.0)\mathrm{MeV}/c^2$ and a width of $(101.4_{-19.7}^{+25.3}\pm 10.2)\mathrm{MeV}$, where the first errors are statistical and second ones are systematic. The first resonance agrees with the $Y(4260)$ resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ for the first time. The statistical significance of this resonance is estimated to be larger than $7.6\sigma$. The mass and width of the second resonance agree with the $Y(4360)$ resonance reported by the BABAR and Belle experiments within errors. Finally, the $Y(4008)$ resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

Figure 1

Measured cross section $\sigma (e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi )$ and simultaneous fit to the $XYZ$ data (left) and scan data (right) with the coherent sum of three Breit-Wigner functions (red solid curves) and the coherent sum of an exponential continuum and two Breit-Wigner functions (blue dashed curves). Dots with error bars are data.