Study of the reaction e^+ e^− → ψ(2S)π^+ π^− via initial-state radiation at BaBar

Abstract

We study the process e^+ e^− →ψ(2S)π^+ π^− 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 Υ(nS) (n=2,3,4) resonances and correspond to an integrated luminosity of 520  fb^(−1). We investigate the ψ(2S)π^+ π^− mass distribution from 3.95 to 5.95  GeV/c^2, and measure the center-of-mass energy dependence of the associated e^+ e^− →ψ(2S)π^+ π^− cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the ψ(2S)π^+ π^− mass distribution corresponding to the decay mode ψ(2S)→J/ψπ^+ π^− yields a mass value of 4340±16 (stat) ±9 (syst)  MeV/c^2 and a width of 94±32 (stat) ±13 (syst)  MeV for the first resonance, and for the second a mass value of 4669±21 (stat) ±3 (syst)  MeV/c^2   and a width of 104±48 (stat) ±10 (syst)  MeV . In addition, we show the π^+ π^− mass distributions for these resonant regions.

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