MEASUREMENT OF THE RELATIVE TOTAL HADRONIC CROSS-SECTION R AT PETRA

We report the first measurement of the ratio R=(σe+e-→hadrons) (σe+e-→μ+μ-) (with negligible τ-lepton contribution) at a center-of-mass energy s=13 GeV and s=17 GeV, from the just finished electron-positron colliding-beam facility PETRA. The detector, MARK-J, has an approximately 4π solid angle and measures γ, e, μ, and charged and neutral hadrons simultaneously. Our results yield R(s=17 GeV)=4.9±0. 6(statistical)±0.7(systematic error), and R(s=13 GeV)=4.6±0.5 (statistical)±0.7(systematic error). The ratio R(s=17 GeV)R(s=13 GeV) is 1.08±0.18. © 1979 The American Physical Society.