A measurement of muon pair production ine+e− annihilation at centre of mass energies 35.0≤\(\sqrt s \)≤46.8 GeV

The reactione+e−→µ+µ− has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction ofRμμ=σμμ/σo=0.932±0.018±0.044 andAμμ=(−10.6 −2.3 +2.2 ±0.5)%. At 38.3 GeV we findRμμ=0.951±0.072 −0.057 +0.063 andAμμ=(+1.7 −8.6 +8.5 ±0.5)%. At 43.6 GeV we measureRμμ=0.921±0.037±0.055 andAμμ=(−17.6 −4.3 +4.4 ±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions.