New results on the reaction e+e−→μ+μ− at √s =29 GeV

Abstract

We have measured the process $e^{+}$ $e^{\mathrm{-}}$→${\mu }^{+}$ ${\mu }^{\mathrm{-}}$ at √s =29 GeV using the High Resolution Spectrometer at SLAC PEP. The forward-backward charge asymmetry is $A_{\mu \mu }$=-(4.9±1.5±0.5)% based on 5057 events. A subsample of 3488 ${\mu }^{+}$ ${\mu }^{\mathrm{-}}$ events in the angular range ‖cosθ‖<0.55 gives a cross-section ratio of $R_{\mu \mu }$=0.990±0.017±0.030. The resulting couplings of the weak neutral current are $g_a^e$ $g_a^{\mu }$=0.208±0.064± 0.021 and $g_v^e$ $g_v^{\mu }$=0.027 ±0.051±0.089. The QED cutoff parameters are ${\Lambda }_{+}$>170 GeV and ${\Lambda }_{\mathrm{-}}$>146 GeV at 95% C.L.