By analyzing the data collected at the center-of-mass energy $E_{\mathrm{cm}}=3.773\mathrm{GeV}$ and below the $D\overline{D}$ meson pair production threshold with the BES-II detector at the BEPC Collider, we directly measured the observed non-$D\overline{D}$ cross section of $\psi (3770)$ decay to be ${\sigma }_{\psi (3770)\to \mathrm{non}\mathrm{\text{−}}D\overline{D}}^{\mathrm{obs}}=(0.95\pm 0.35\pm 0.29)\mathrm{nb}$ at $E_{\mathrm{cm}}=3.773\mathrm{GeV}$, and the branching fraction $BF[\psi (3770)\to \mathrm{non}\mathrm{\text{−}}D\overline{D}]=(13.4\pm 5.0\pm 3.6)\%$ for inclusive non-$D\overline{D}$ decay of $\psi (3770)$. We also determined the cross section for $D\overline{D}$ meson pair production to be ${\sigma }_{D\overline{D}}^{\mathrm{obs}}=(6.12\pm 0.37\pm 0.23)\mathrm{nb}$ at $E_{\mathrm{cm}}=3.773\mathrm{GeV}$.

• Received 24 August 2007

DOI:https://doi.org/10.1103/PhysRevD.76.122002