Measurement of the Relative Total Hadronic Cross Section<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi></mml:math>at PETRA

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