/ hep-ex arXiv:1611.01317

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

Pages: 10

Abstract: 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 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 $(4222.0\pm 3.1\pm 1.4)$~MeV/$c^2$ and a width of $(44.1\pm 4.3\pm 2.0)$~MeV, while the second one has a mass of $(4320.0\pm 10.4 \pm 7.0)$~MeV/$c^2$ and a width of $(101.4^{+25.3}_{-19.7}\pm 10.2)$~MeV, where the first errors are statistical and second ones systematic. The first resonance is near $4.22$~GeV/$c^2$, corresponding to the so-called $Y(4260)$ resonance reported by previous experiments. However, our measured mass is lower and the width is narrower than previous measurements. The second structure is observed in $e^+e^-\to \pi^+\pi^-J/\psi$ for the first time. The statistical significance is estimated to be larger than $7.6\sigma$.

Note: 8 pages, 1 figure

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