Tau lepton physics at LEP

The talk covers three contributions on (i) the final measurement of branching ratios and spectral functions of t decays using the full LEP-I data from ALEPH, (ii) a preliminary measurement of the t hadronic branching ratios from DELPHI and (iii) a measurement of the strange spectral function in hadronic t decays from OPAL. These measurements are discussed and the relevant physics topics are briefly reviewed.Comment: Presented at the International Europhysics Conference on High Energy Physics (EPS-HEP2005), Lisboa, Portugal, July 21-27, 2005, On behalf of the ALEPH, DELPHI and OPAL Collaboration

Search for Charged Higgs bosons: Preliminary Combined Results Using LEP data Collected at Energies up to 209 GeV

In the year 2000 the four LEP experiments have collected 870 pb-1 of data at energies between 200 and 209 GeV, with about 510 pb-1 above 206 GeV. These data have been combined with data sets collected earlier at lower energies. %The following 95% confidence level bounds have been obtained. For charged Higgs bosons predicted by two-doublet extensions of the Standard Model and decaying only into the channels H+->csbar and tau+nutau, a lower mass bound of 78.6 GeV is obtained, at the 95% confidence level.Comment: 9 pages, 4 figures, figures supplied as .eps files. Note submitted to the EPS '01 conference in Budapest, and the Lepton-Photon '01 conference in Rom

Searches for Higgs Bosons Decaying into Photons: Preliminary Combined Results Using LEP Data Collected at Energies up to 209 GeV

This note describes preliminary LEP-combined results of searches for Higgs bosons decaying into photons. The analyses use data collected at sqrt(s)~88-209 GeV. Using the combined data for H -> gamma gamma, a lower bound of 108.2 GeV is set at the 95% confidence level for the ``benchmark'' fermiophobic Higgs boson.Comment: 7 pages, 4 figures. Figures are supplied as .eps files. Submitted to the EPS '01 conference in Budapest, and the Lepton-Photon '01 conference in Rom

A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model

This note presents a combination of published and preliminary electroweak results from the four LEP collaborations ALEPH, DELPHI, L3 and OPAL based on electron-positron collision data taken at centre-of-mass energies above the Z-pole, 130 \GeV to 209 \GeV (\LEPII), as prepared for the 2006 summer conferences. Averages are derived for di-fermion cross sections and forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and single-Z cross sections, electroweak gauge boson couplings, W mass and width and W decay branching ratios. An investigation of the interference of photon and Z-boson exchange is presented, and colour reconnection and Bose-Einstein correlation analyses in W-pair production are combined. The main changes with respect to the experimental results presented in 2005 are new preliminary combinations of final {\LEPII} results on the mass and width of the W boson. Including the precision electroweak measurements performed at the Z pole published recently, the results are compared with precise electroweak measurements from other experiments, notably CDF and D{\O}at the Tevatron. Constraints on the input parameters of the Standard Model are derived from the results obtained in high-$Q^2$ interactions, and used to predict results in low-$Q^2$ experiments, such as atomic parity violation, M{\"o}ller scattering, and neutrino-nucleon scattering.Comment: 173 pages; v2: Update of titlepage and addition of two reference

Combination procedure for the precise determination of Z boson parameters from results of the LEP experiments

The precise determination of the Z boson parameters from the measurements at the Z resonance by the four collaborations ALEPH, DELPHI, L3 and OPAL in e+e- collisions at the large electron positron collider LEP at CERN is a landmark for precision tests of the electroweak theory. The four experiments measured quantities which were used to extract the mass and width of the Z boson, the hadronic cross-section at the pole of the resonance, the ratio of hadronic and leptonic decay widths, and the leptonic forward-backward asymmetries at the pole. The combination procedure based on these parameters is presented in this paper.Comment: 41 pages, 4 figure

Search for the Standard Model Higgs Boson at LEP

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have collected 2465 pb-1 of e+e- collision data at energies between 189 and 209 GeV, of which 542 pb-1 were collected above 206 GeV. Searches for the Standard Model Higgs boson have been performed by each of the LEP collaborations. Their data have been combined and examined for their consistency with the Standard Model background and various Standard Model Higgs boson mass hypotheses. A lower bound of 114.1 GeV has been obtained at the 95% confidence level for the mass of the Higgs boson. The likelihood analysis shows a preference for a Higgs boson with a mass of 115.6 GeV. At this mass, the probability for the background to generate the observed effect is 3.4%.Comment: 27 pages, 13 figures. Figures supplied as .eps files. This note summarizes the LEP combined SM Higgs search results to be presented at EPS01 in Budapest, and at Lepton-Photon '01 in Rome. Submitted to CERN-EP preprints First update (v2): remove extraneous .eps files Second update (v3): Some minor corrections. 1-CLb(mh=115.6) -> 3.4% (was 3.5% before), "test signal curve" in fig. 1 updated. Cosmetic changes to figures v4: change word "revise" to "review" (was written assuming British meaning of the word

Flavour Independent Search for Hadronically Decaying Neutral Higgs Bosons at LEP

Hadronic decays of Higgs bosons, not necessarily into b-quarks, have been searched for using data collected at LEP-2. Such searches are complementary to the usual Standard Model Higgs searches and lead to more model-independence. Preliminary results obtained by the four LEP collaborations are presented for the hZ production mechanism (using the q-qbarq-qbar, q-qbarnu-nubar and q-qbarl+l- channels) and combined for the first time.Comment: 7 pages, 2 figures. Figures are supplied as .eps files. Sumbitted to the EPS '01 conference in Budapest, and the Lepton-Photon '01 conference in Rom

Searches for Invisible Higgs bosons: Preliminary combined results using LEP data collected at energies up to 209 GeV

In the year 2000 the four LEP experiments have collected data at energies between 200 and 209 GeV, for approximately 868 pb-1 integrated luminosity. The LEP working group for Higgs boson searches has combined these data with earlier data sets collected at lower centre-of-mass energies to search for a neutral CP-even Higgs boson, produced at the Standard Model rate, decaying into "invisible" particles. No statistically significant excess has been observed when compared to the Standard Model background prediction, and assuming that the Higgs boson decays only into such states a lower bound has been set on its mass at 95% confidence level of 114.4 GeV.Comment: 7 pages, 5 figures, figures supplied as .eps files. Submitted to the EPS '01 conference in Budapest and the Lepton-Photon '01 conference in Rome. Version 2 adds theoretical citation

Searches for the Neutral Higgs Bosons of the MSSM: Preliminary Combined Results Using LEP Data Collected at Energies up to 209 GeV

In the year 2000 the four LEP experiments collected data at centre-of-mass energies between 200 and 209 GeV, integrating approximately 870 pb-1 of luminosity, with about 510 pb-1 above 206 GeV. The LEP working group for Higgs boson searches has combined these data with data sets collected previously at lower energies. In representative scans of the parameters of the Minimal Supersymmetric Standard Model (MSSM), the mass limits mh>91.0 GeV and mA>91.9 GeV are obtained for the light CP-even and the CP-odd neutral Higgs boson, respectively. For a top quark mass less than or equal to 174.3 GeV, assuming that the stop quark mixing is maximal, and choosing conservative values for other SUSY parameters affecting the Higgs sector, the range 0.5<tanbeta<2.4 is excluded. Additionally, the results of flavour-independent searches for hadronically decaying Higgs bosons are included, allowing exclusion of MSSM models with suppressed decays of the Higgs bosons to pairs of b quarks.Comment: 20 Pages, 8 figures. Submitted to EPS'01 in Budapest and Lepton-Photon '01 in Rome. Figures supplied as .eps files, including separate color version

A Combination of Preliminary Electroweak Measurements and Constraints on the Standard Model

This note presents a combination of published and preliminary electroweak results from the four LEP collaborations and the SLD collaboration which were prepared for the 2002 summer conferences. Averages from Z resonance results are derived for hadronic and leptonic cross sections, the leptonic forward-backward asymmetries, the tau polarisation asymmetries, the b-bbar and c-cbar partial widths and forward-backward asymmetries and the q-qbar charge asymmetry. Above the Z resonance, averages are derived for di-fermion cross sections and forward-backward asymmetries, photon-pair, W-pair, Z-pair, single-W and single-Z cross sections, electroweak gauge boson couplings, W mass and width and W decay branching ratios. The main changes with respect to the experimental results presented in summer 2001 are updates to the Z-pole heavy flavour results from SLD and LEP, and new combinations of results above the Z pole. A new investigation of the interference of photon and Z-boson exchange is presented. For the first time, colour reconnection and Bose-Einstein correlation analyses in W-pair production are combined. The results are compared with precise electroweak measurements from other experiments, notably the recent final result on the electroweak mixing angle determined in neutrino-nucleon scattering by the NuTeV collaboration. The parameters of the Standard Model are evaluated, first using the combined LEP electroweak measurements, and then using the full set of electroweak results.Comment: 216 pages; v2: add CERN EP preprint number to title page; v3: small corrections to author list, text and reference