Study of the reaction e^{+}e^{-}->psi(2S)pi^{-}pi^{-} via initial state radiation at BaBar

Abstract

We study the process $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the \BaBar detector at center-of-mass energies at and near the ${\rm Y}(\mathrm{nS})$ (n = 2, 3, 4) resonances and correspond to an integrated luminosity of 520$f{b}^{-}$. We investigate the $\psi (2S){\pi }^{+}{\pi }^{-}$ mass distribution from 3.95 to 5.95 $GeV/c^2$, and measure the center-of-mass energy dependence of the associated $e^{+}{e}^{-}\to \psi (2S){\pi }^{+}{\pi }^{-}$ cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the $\psi (2S){\pi }^{+}{\pi }^{-}$ mass distribution corresponding to the decay mode $\psi (2S)\to J/\psi {\pi }^{+}{\pi }^{-}$ yields a mass value of $4340\pm 16$ (stat) $\pm 9$ (syst) $MeV/{\mathrm{c}}^{2}andawidthof$94 \pm 32$(stat)$\pm 13$(syst)MeVforthefirstresonance,andforthesecondamassvalueof$4669 \pm 21$(stat)$\pm 3$(syst)${\mathrm {MeV/c^{2}}}$andawidthof$104 \pm 48$(stat)$\pm 10$(syst)MeV.Inaddition,weshowthe$pi^{+}π^{-}$ mass distributions for these resonant regions.

6 pages, 8 figures, submitted to Phys. Rev. D (Rapid Communications)