First study of the interference between initial and final state radiation at the Z resonance

The interference between initial and final state radiation in the process e(+)e(-) –> mu(+)mu(-) at root s approximate to M(Z) has been studied by measuring the forward-backward asymmetry as a function of the acoplanarity angle between the final state muons. The interference is expected to be sensitive to the space-time separation of the initial and final state radiation. The measured asymmetry distribution has been compared to theoretical predictions using the KORALZ generator, with and without O(alpha) interference, The magnitude of the interference between initial and final state radiation was found to be of the order predicted and to follow the expected distribution. Using the theoretical predictions, a value of Gamma(Z) = 2.50 +/- 0.21 (stat.) +/- 0.06 (syst.) GeV. has been extracted, The interpretation of this result is discussed. There is an additional uncertainty in the estimate of Gamma(Z) from as yet uncalculated higher order interference terms. By assuming a value of Gamma(Z) consistent with the world average, the data were used to estimate the size of these uncalculated corrections

CHARGED KAON PRODUCTION IN TAU-DECAYS AT LEP

Kaon production in one prong tau decays has been studied using data collected with the DELPHI detector at the LEP collider. Charged kaons were identified over a large momentum range by the DELPHI barrel Ring Imaging Cherenkov detector. The following branching ratios have been determined: BR(tau –> Knu(T)) = (0.85 +/- 0.18) %, BR(tau –> Knu(tau) greater-than-or-equal-to 0 neutrals) = (1.54 +/- 0.24) %, BR(tau –> Knu(tau) greater-than-or-equal-to 1 neutrals) = (0.69 +/- 0.25) %. The result for the exclusive branching ratio is consistent with the Standard Model prediction based on tau - mu - e universality. In addition, tau decay into K*- was studied in the channel K*- –> K- pi0. The result BR(tau –> K*-nu(tau)) x BR(K*- –> K- pi0) = (0.57 +/- 0.23)% was obtained