Measurement of the Relative Total Hadronic Cross SectionRat PETRA

We report the first measurement of the ratio $R=\frac{\left({\sigma }_{e^{+}{e}^{-}\to \mathrm{hadrons}}\right)}{\left({\sigma }_{e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}}\right)}$ (with negligible $\tau$-lepton contribution) at a center-of-mass energy $\sqrt{s}=13\mathrm{}$ GeV and $\sqrt{s}=17\mathrm{}$ GeV, from the just finished electron-positron colliding-beam facility PETRA. The detector, MARK-J, has an approximately $4\pi$ solid angle and measures $\gamma$, $e$, $\mu$, and charged and neutral hadrons simultaneously. Our results yield $R(\sqrt{s}=17\mathrm{} \mathrm{GeV})=4.9\mathrm{}\pm 0.6 \mathrm{}\left(\mathrm{statistical}\right)\mathrm{} \pm 0.7 \left(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{e}\mathrm{r}\mathrm{r}\mathrm{o}\mathrm{r}\right)$, and $R(\sqrt{s}=13\mathrm{} \mathrm{GeV})=4.6\mathrm{}\pm 0.5 \mathrm{}\left(\mathrm{statistical}\right)\mathrm{} \pm 0.7 \left(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{ }\mathrm{e}\mathrm{r}\mathrm{r}\mathrm{o}\mathrm{r}\right)$. The ratio $\frac{R(\sqrt{s}=17\mathrm{} \mathrm{GeV})}{R(\sqrt{s}=13\mathrm{} \mathrm{GeV})}$ is 1.08±0.18.