Search for Structure in $\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})$ between $\sqrt{s}=10.34\mathrm{} \mathrm{and} 11.6$ GeV

The CUSB detector at the Cornell Electron Storage Ring has been used to measure $R=\frac{\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})}{\sigma (e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-})}$ in the c.m. energy regions between the ${\Upsilon }^{\prime \prime }$ and the ${\Upsilon }^{\prime \prime \prime }$, and above the ${\Upsilon }^{\prime \prime \prime }$ up to $\sqrt{s}=11.6\mathrm{}$ GeV, with integrated luminosities of 5000 and 2100 ${\mathrm{nb}}^{-1\mathrm{}}$, respectively. No narrow resonances are observed, and limits on the leptonic widths are presented. The average value of $R$ increases by 0.31±0.06 across the flavor threshold.