Observation of Double cc bar Production in e+ e- Annihilation at sqrt{s} ~ 10.6 GeV

Abstract

We report the observation of prompt J/psi via double ccbar production from the e+e- continuum. In this process one ccbar pair fragments into a J/psi meson while the remaining pair either produces a bound charmonium state or fragments into open charm. Both cases have been observed: the first by studying the mass spectrum of the system recoiling against the J/psi, and the second by reconstructing the J/psi together with a charmed meson. We find cross-sections of σ(e+ e- -> J/psi eta_c (gamma)) * BR (eta_c -> >=4 charged) = 0.033 (+0.007 -0.006)(stat) \pm 0.009(syst)pb and σ(e+ e- -> J/psi D*+ X) = 0.53 (+0.19 -0.15)(stat) \pm 0.14(syst) pb, and infer σ(e+ e- -> J/psi c cbar) / σ(e+ e- -> J/psi X) = 0.59 (+0.15 -0.13)(stat) \pm 0.12(syst). These results are obtained from a 46.2/fb data sample collected near the Upsilon(4S) resonance, with the Belle detector at the KEKB asymmetric energy e+ e- collider.

Figures (2)

• Figure 1: a) The recoil mass distribution for the $J/\psi$ signal region (points) and scaled sidebands (shaded histogram). The inset shows the MC reconstruction efficiency for $e^+e^- \rightarrow J/\psi\,q\bar{q}$ ($q = u,d,s$; open circles) and $e^+e^- \rightarrow J/\psi\,c\bar{c}$ events (closed circles). b) The recoil mass distribution after refitting the $J/\psi$ candidate with a mass constraint for the $J/\psi$ signal region (points) and scaled sidebands (shaded histogram). The curve represents the fit described in the text.
• Figure 2: Results of a search for associated production of $J/\psi$ and charm mesons: a) the scatter plot $M(l^{+}l^{-})$ vs $M(D^0 \pi^+)$; b) projection onto the $M(D^0 \pi^+)$ axis; c) the scatter plot $M(l^{+}l^{-})$ vs $M(K^- \pi^+ (K^+ K^-))$; d) projection onto the $M(K^- \pi^+ (K^+ K^-))$ axis. Points with error bars show the $J/\psi$ signal region and the shaded histograms show the scaled sidebands. The curves represent the fit described in the text.