Measurement of the e+e- -> J/psi ccbar cross section at \sqrt{s} ~10.6 GeV

Abstract

We present a new measurement of the e+e- -> J/psi ccbar cross section where the ccbar pair can fragment either into charmed hadrons or a charmonium state. In the former case the J/psi and a charmed hadron are reconstructed, while the latter process is measured using the recoil mass technique, which allows the identification of two-body final states without reconstruction of one of the charmonia. The measured e+e- -> J/psi ccbar cross section is (0.74 +- 0.08 + 0.09 - 0.08) pb, and the e+e- -> J/psi non-ccbar cross section is (0.43 +- 0.09 +-0.09) pb. We note that the measured cross sections are obtained from a data sample with the multiplicity of charged tracks in the event larger than four; corrections for the effect of this requirement are not performed as this cannot be done in a model-independent way. The analysis is based on a data sample with an integrated luminosity of 673/fb recorded near the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- asymmetric-energy collider.

Figures (4)

• Figure 1: The mass of the system recoiling against the reconstructed a) $J/\psi$, b) $\psi^\prime$, c) $\chi_{c1}$ and d) $\chi_{c2}$. The curves show the fit results described in the text.
• Figure 2: $M_{\ell^+ \ell^-}$ spectra for $H_c$ signal (points with errors) and scaled $H_c$ sideband windows (histograms), where $H_c$= a) $D^0$, b) $D^+$, c) $D^+_s$ and d) $\Lambda_c^+$. The curves represent the result of the fit; solid curves correspond to the $H_c$ signal windows, and dashed curves to the $H_c$ sidebands.
• Figure 3: $J/\psi$ momentum spectra: a) inclusive (open circles), from $e^+ e^- \to J/\psi \, H_c \, X$ (filled squares) and from double charmonium production (filled circles); b) the sum of all $e^+ e^- \to J/\psi \,{c\bar{c}}$ processes (open squares), from the $e^+ e^- \to \hbox{$J/\psi \, X_{\text{non-}c\bar{c}}$}$ processes (filled triangles). The results of fits to the Peterson function are shown in a) for the inclusive spectrum (solid curve); in b) for the processes $e^+ e^- \to J/\psi \,{c\bar{c}}$ (solid curve), and $e^+ e^- \to \hbox{$J/\psi \, X_{\text{non-}c\bar{c}}$}$ (dashed curve).
• Figure 4: Angular distributions ($\left|\cos\theta_{\rm{hel}}\right|$ in a), $\left|\cos\theta_{\rm{prod}}\right|$ in b)) for inclusive $e^+ e^- \to J/\psi \, X$ (open circles), $e^+ e^- \to J/\psi \,{c\bar{c}}$ (open squares), and $e^+ e^- \to \hbox{$J/\psi \, X_{\text{non-}c\bar{c}}$}$ processes (filled triangles). The results of the fits described in the text are shown with the dash-dotted, solid, and dashed curves respectively.