Study of the pi+pi-J/psi Mass Spectrum via Initial-State Radiation at BABAR

Abstract

We present an update of the study of the Y(4260) resonance, produced in the process $e^+e^-\to\gamma_{ISR} \pi^+\pi^-J/\psi$ using initial-state radiation events at the PEP-II $e^+e^-$ storage rings. This study is based on 454fb$^{-1}$ of data recorded with the {\slshape B\kern-0.1em{\smaller A}\kern-0.1em B\kern-0.1em{\smaller A\kern-0.2em R}} detector at a center-of-mass energy in the $\Upsilon(4S)$ resonance region. From a fit with a single non-relativistic Breit-Wigner shape we obtain updated parameters for the Y(4260) resonance which are $m_Y = 4252 \pm6 ^{+2}_{-3}$MeV/c$^2$ and $\Gamma_Y = 105 \pm 18^{+4}_{-6}$MeV/c$^2$; we also measure ${\calB}(\pi^+\pi^-J/\psi)\Gamma_{e^+e^-} = (7.5\pm 0.9 \pm0.8)$ eV. We cannot confirm the recent BELLE observation of a broad structure around 4.05GeV/c$^2$ in this decay mode.