Measurements of the observed cross sections for exclusive light hadron production in e+e− annihilation at s=3.773 and 3.650 GeV

By analyzing the data sets of 17.3 pb−1 taken at s = 3.773 GeV and 6.5 pb−1 taken at s = 3.650 GeV with the BESII detector at the BEPC collider, we have measured the observed cross sections for 12 exclusive light hadron final states produced in e + e − annihilation at the two energy points. We have also set the upper limits on the observed cross sections and the branching fractions for ψ ( 3770 ) decay to these final states at 90% C.L.