Precision determination of the electroweak mixing angle and test of neutral current universality from the tau polarization measurements at OPAL




Graham, Kevin

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Measurements of the Ƭ lepton polarization and forward-backward polarization asymmetry near the Z° resonance using the OPAL detector are described. The measurements are based on analyses of [special characters omitted] decays from a sample of 144, 810 [special characters omitted] candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the Ƭ lepton decays according to V-A theory, the average Ƭ polarization near [special characters omitted] is measured to be [special characters omitted] = (-14.10 ± 0.73 ± 0.55)% and the Ƭ polarization forward-backward asymmetry to be [special characters omitted] = (-10.55 ± 0.76 ± 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z° interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: AƬ = 0.1466 ± 0.0076 ± 0.0057, Ae = 0.1464 ± 0.0108 ± 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give [special characters omitted] = 0.1455 ± 0.0073. Within the context of the standard model this combined result corresponds to sin [special characters omitted] = 0.23172 ± 0.00092. Combining these results with those from the other OPAL neutral current measurements yields a value of sin [special characters omitted] = 0.23211 ± 0.00068.



Heavy particles (Nuclear physics), Kaons, Radioactive decay