Tau and Charm Physics Highlights

In τ physics, we are at the frontier between the completion of the LEP program and the start of analyses from b-factories, which are expected to produce results in the coming years. Nice results from CLEO are steadily delivered in the meantime. For charm, impressive progress have been achieved by fixed target experiments in the search for CP violation and D • − D • oscillations. First results from b-factories demonstrate the power of these facilities in such areas. The novel measurement of the D * width by CLEO happens to be rather different from current expectations. The absence of a charm factory explains the lack or the very slow progress in the absolute scale determinations for charm decays. 1 Tau physics τ physics is an extremely rich area. In the following, I will consider the tests of lepton couplings universality to weak vector bosons, in light of recent measurements. In a different domain, τ decays into two pions play a special role as they can be related to e + −e − annihilation into hadrons (I=1 component) and thus provide an accurate determination of the pion form factor. It can be noted that, in τ decays , measurements are obtained within the same experimental running conditions and that hadronic decays are normalized relative to leptonic decays. These favourable circumstances allow, in general, a better control of systematics as compared with experiments operating at low energy e + − e − machines which need to run at different energies and have to determine an absolute normalization for each energy point. These properties have been used to reduce uncertainties related to the virtual photon hadronic component in the evaluation of, for instance, the muon anomalous magnetic moment. Hadron production in τ decays, through the charged weak current , is theoretically " clean " and allows to measure α s (m 2 τ) and to determine the value of the strange quark mass. Because of the time allocated for this presentation , I was unable to cover other topics as the detailed spectroscopy of hadronic states in n π; n ≥ 3 decays, recent results on the Lorentz structure in leptonic decays 1 and new measurements of topological branching fractions 2. Results presented in this review have been obtained by analysing a few 10 5 τ pairs in each LEP collaboration and a few 10 6 events in CLEO. In future a …