Study of the reaction e+e- → ψ (2S)π+π- via initial-state radiation at B a B ar

Abstract

We study the process e + e − → ψ ( 2 S ) 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 ( 2 S ) 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 ( 2 S ) π + π − cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the ψ ( 2 S ) π + π − mass distribution corresponding to the decay mode ψ ( 2 S ) → J / ψ π + 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.