Observation of a Near-Threshold Enhancement in the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\Lambda}}_{c}^{+}{\ensuremath{\Lambda}}_{c}^{\ensuremath{-}}$ Cross Section Using Initial-State Radiation

Observation of a Near-Threshold Enhancement in the $e^{+} e^{-} \to Λ_{c}^{+} Λ_{c}^{-}$ Cross Section Using Initial-State Radiation

G. Pakhlova et al. (The Belle Collaboration)

Phys. Rev. Lett. 101, 172001 – Published 24 October 2008

Abstract

We report a measurement of the exclusive $e^{+} e^{-} \to Λ_{c}^{+} Λ_{c}^{-}$ cross section as a function of center-of-mass energy near the $Λ_{c}^{+} Λ_{c}^{-}$ threshold. A clear peak with a significance of $8.2 σ$ is observed in the $Λ_{c}^{+} Λ_{c}^{-}$ invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of $M = [4634_{- 7}^{+ 8} (stat)_{- 8}^{+ 5} (syst)] MeV / c^{2}$ and $Γ_{tot} = [92_{- 24}^{+ 40} (stat)_{- 21}^{+ 10} (syst)] MeV$ are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the $Υ (4 S)$ resonance and nearby continuum with an integrated luminosity of $695 {fb}^{- 1}$ at the KEKB asymmetric-energy $e^{+} e^{-}$ collider.