Search for charged Higgs bosons in e+e- collisions at energies up to sqrt(s) = 209GeV

A search for charged Higgs bosons produced in pairs is performed with data collected at centre-of-mass energies ranging from 189 to 209 GeV by ALEPH at LEP, corresponding to a total luminosity of 629 invpb. The three final states taunutaunu, taunucs and cscs are considered. No evidence for a signal is found and lower limits are set on the mass M_H+ as a function of the branching fraction B(H to taunu). In the framework of a two-Higgs-doublet model, and assuming B(H+ to taunu + B(H+ to cs) = 1 charged Higgs bosons with masses below 79.3 Gev/c2 are excluded at 95% confidence level independently of the branching ratios

Event shapes and power corrections in e+e- annihilitions

Hadronic final states in e+e- annihilitions at centre-of-mass energies from 14GeV up to 189GeV are studied in order to test recent predictions for power corrections to the mean values as well as the distributions of event shape variables.Comment: 3 pages, 3 figures, DIS99 Workshop, Berlin, Germany, April 19-23, 199

Lepton non-universality at LEP and charged Higgs

A recent analysis of the LEP data shows an interesting deviation from lepton universality in W boson decays. An excess at the level of 2.8 sigma is found in the tau mode branching ratio with respect to the other two modes. It is suggested that this seeming lepton non-universality might stem from pair production of charged Higgs bosons almost degenerate with W, that preferentially decay to heavy fermions. It is shown that the deviation can be reduced to 1.4 sigma in two Higgs doublet model I without any conflict with the existing direct or indirect constraints. This conclusion is largely independent of tan beta, the ratio of Higgs vacuum expectation values. This scenario can be tested at the forthcoming international linear collider.Comment: 16 pages, published version with minor change

Spin Physics at e^+e^- Colliders

A large number of measurements with polarized beams and/or spin analysis of final state particles has been performed at the e^+e^- colliders LEP and SLC, providing important information on the dynamics of high energy interactions. In this paper three subjects, for which the role of spin studies was particularly relevant, will be covered: the measurements of the electroweak couplings, the study of fragmentation dynamics and the search for physics beyond the Standard Model.Comment: 11 pages, Invited talk given at the International Workshop on Symmetry and Spin - Prague, Czech Republic, August 30 - September 5, 199

Signals of Z' boson in the Bhabha process within the LEP2 data set

The LEP2 data set on the Bhabha process is analyzed with the aim to detect the signals of the heavy virtual Z' gauge bosons. The state interacting with the left-handed standard-model doublets and called the Chiral Z' is investigated. This particle was introduced already as the low-energy state allowed by the renormalizability of the model. The contribution of the Chiral Z' state to the Bhabha process is described by two parameters: the coupling to electrons and the Z-Z' mixing angle. The sign-definite one-parameter observable is proposed to measure the Z' coupling to the electron current. The one-parameter fit of the data shows no signals of the particle. The alternative two-parameter fit of the differential cross-sections is also performed. It also shows no Chiral Z' signals. The comparisons with other fits are discussed.Comment: 15 pages, 4 figures. The paper was completely rewritten on the base of new dat