Study of the Reaction e⁺e⁻ → ψ(2S)π⁺π⁻ via Initial-State Radiation at BaBar


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/c², 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/c² 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/c² and a width of 104 ± 48 (stat) ±10 (syst) MeV. In addition, we show the π⁺ π⁻ mass distributions for these resonant regions.



Branching fractions (Nuclear physics), Atomic mass


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