Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be:m(w) = 80.376 +/- 0.033 GeVGamma(w) = 2.195 +/- 0.083GeV B(W -> had) = 67.41 +/- 0.27%g(1)(Z) = 0.984(-0.020)(+0.018)K-gamma - 0.982 +/- 0.042lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.

A search for the production and non-standard decay of a Higgs boson, h, into four taus through intermediate pseudoscalars, a, is conducted on 683 pb−1 of data collected by the ALEPH experiment at centre-of-mass energies from 183 to 209 GeV. No excess of events above background is observed, and exclusion limits are placed on the combined production cross section times branching ratio, \( {\xi^2} = \frac{{\sigma \left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}}{{{\sigma_{\text{SM}}}\left( {{\text{e}^{+} }{\text{e}^{-} } \to {\text{Zh}}} \right)}} \times B\left( {h \to {\text{aa}}} \right) \times B{\left( {{\text{a}} \to {\tau^{+} }{\tau^{-} }} \right)^2} \). For m h < 107 GeV/c 2 and 4 < m a < 10 GeV/c 2, ξ 2 > 1 is excluded at the 95% confidence level.

The ZZ production cross section is measured from a data sample corresponding to a total integrated luminosity of 452 pb−1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 192 to 209 GeV. Individual cross sections, extracted at six centre-of-mass energies, are found to be in agreement with Standard Model calculations. The results are used to set limits on anomalous neutral gauge couplings.

Inclusive beauty-quark production in two-photon collisions has been measured at LEP using an integrated luminosity of 698 pb-1 collected by the ALEPH detector with sqrt(s) between 130 and 209 GeV. The b quarks were identified using lifetime information. The cross section is found to be sigma(e+ e- --> e+ e- b \bar{b} X) = (5.4 +/- 0.8 (stat) +/- 0.8 (syst)) pb which is consistent with Next-to-Leading Order QCD.

Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LER The production rate of anti-deuterons is measured to be (5.9 +/- 1.8 +/- 0.5) x 10(-6) per hadronic Z decay in the anti-deuteron momentum range from 0.62 to 1.03 GeV/c. The coalescence parameter B-2, which characterizes the likelihood of anti-deuteron production, is measured to be 0.0033 +/- 0.0013 GeV2 in Z decays. These measurements indicate that the production of anti-deuterons is suppressed in e(+)e(-) collisions compared to that in pp and photoproduction collisions. (c) 2006 Elsevier B.V. All rights reserved.

The full LEP-1 data set collected with the ALEPH detector at the Z pole during 1991–1995 is analysed in order to measure the τ decay branching fractions. The analysis follows the global method used in the published study based on 1991–1993 data, but several improvements are introduced, especially concerning the treatment of photons and π0's. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to over 300 000 measured and identified τ decays. Branching fractions are obtained for the two leptonic channels and 11 hadronic channels defined by their respective numbers of charged particles and π0's. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied to the hadronic channels to derive branching ratios for exclusive final states without kaons. Thus the analyses of the full LEP-1 ALEPH data are combined to yield a complete description of τ decays, encompassing 22 non-strange and 11 strange hadronic modes. Some physics implications of the results are given, in particular related to universality in the leptonic charged weak current, isospin invariance in a1 decays, and the separation of vector and axial-vector components of the total hadronic rate. Finally, spectral functions are determined for the dominant hadronic modes and updates are given for several analyses. These include: tests of isospin invariance between the weak charged and electromagnetic hadronic currents, fits of the ρ resonance lineshape, and a QCD analysis of the non-strange hadronic decays using spectral moments, yielding the value αs(mτ2)=0.340±0.005exp±0.014th. The evolution to the Z mass scale yields αs(MZ2)=0.1209±0.0018. This value agrees well with the direct determination from the Z width and provides the most accurate test to date of asymptotic freedom in the QCD gauge theory.

A search for single sneutrino production under the assumption that R-parity is violated via a single dominant LLĒ coupling is presented. This search considers the process eγ → ν̃ℓ and is performed using the data collected by the ALEPH detector at centre-of-mass energies from 189 GeV up to 209 GeV corresponding to an integrated luminosity of 637.1 pb-1. The numbers of observed candidate events are in agreement with Standard Model expectations and 95% confidence level upper limits on five of the LLĒ couplings are given as a function of the assumed sneutrino mass.

A search for the pseudoscalar meson ηb is performed in two-photon interactions at LEP 2 with an integrated luminosity of 699 pb−1 collected at e+e− centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Γγγ(ηb)×BR(ηb→4charged particles)<48 eV, Γγγ(ηb)×BR(ηb→6charged particles)<132 eV are obtained at 95% confidence level, which correspond to upper limits of 9.0% and 25% on these branching ratios.

Inclusive branching ratios involving b → τ transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio BR(b → τ-ν̄τX) and the semi-inclusive branching ratio BR(b → τ-ν̄τD*±X) are measured to be (2.43 ± 0.20 ± 0.25)% and (0.88 ± 0.31 ± 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions BR(B- → τ-v̄τ) and BR(b → sνν̄) are set to 8.3 × 10-4 and 6.4 × 10-4 at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 (GeV/c2)-1 to be set on the tan β/mH± ratio, in the framework of type-II two-Higgs-doublet models.

A measurement of the Michel parameters and the average vτ helicity in τ lepton decays is described. The data was collected with the ALEPH detector at LEP during the years 1991 to 1995. A total integrated luminosity of 155 pb-1 is analysed. The Michel parameters ρl, ξl, (ξδ)l (l = e, μ), and ημ are determined for the leptonic decays, and the chirality parameters ξπ, ξρ, and ξa1 for the hadronic final states. Under the assumptions of e-μ universality and ξπ = ξρ = ξa1, the values ρl = 0.742 ± 0.016, ηl = 0.012 ± 0.026, (ξδ)l = 0.776 ± 0.051, ξl = 0.986 ± 0.074, and ξh = 0.992 ± 0.011 are obtained. No significant deviation is observed from the Standard Model assumption of the V - A structure of the charged weak interaction.

An analysis based on 124 000 selected τ pairs recorded by the ALEPH detector at LEP provides the vector (V) and axial-vector (A) spectral functions of hadronic τ decays together with their total widths. This allows the evaluation of finite energy chiral sum rules that are weighted integrals over the (V - A) spectral functions. In addition, a precise measurement of αs, along with a determination of non-perturbative contributions at the τ mass scale is performed. The experimentally and theoretically most robust determination of αs(Mτ 2) is obtained from the (V + A) fit that yields αs (Mτ 2) = 0.334 ±0.022 giving αs (MZ 2) = 0.1202 ± 0.0027 after the extrapolation to the mass of the Z boson. The approach of the Operator Product Expansion (OPE) is tested experimentally studying the evolution of the τ hadronic widths to masses smaller than the τ mass.

During 1997 the ALEPH experiment at LEP gathered 57 pb(-1) of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e(+)e(-) --> HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m(H) > 87.9 GeV/c(2) at 95% confidence level. (C) 1998 Elsevier Science B.V. All rights reserved.

Using a sample of four million hadronic Z events collected in ALEPH from 1991 to 1995, the decays D8+ --> D(0)pi(s)(+), with D-0 decaying to K- pi(+) or to K+ pi(-), are studied. The relative branching ratio B(D-0 --> K+ pi(-))/B(D-0 --> K- pi(+)) is measured to be (1.84 +/- 0.59(stat.) +/- 0.34(syst.))%. The two possible contributions to the D-0 --> K+ pi(-) decay, doubly Cabibbo-suppressed decays and DO-DO mixing, are disentangled by measuring the proper-time distribution of the reconstructed DO's. Assuming no interference between the two processes, the upper limit obtained on the mixing rate is 0.92% at 95% CL. The possible effect of interference between the two amplitudes is also assessed. (C) 1998 Elsevier Science B.V. All rights reserved.

The data collected by the ALEPH experiment at LEP at centre-of-mass energies around 183 GeV are analysed to search for sleptons, the partners of leptons in supersymmetric theories. The previously published search for acoplanar leptons and missing energy has been updated. New searches have been developed to cover a wider range of slepton signals. These include single electrons, acoplanar leptons accompanied by two photons plus missing energy as well as particles with lifetime. No evidence for the production of any such particles is found. Slepton mass limits are reported within gravity mediated and gauge mediated SUSY breaking scenarios. © 1998 Elsevier Science B.V. All rights reserved.

Final states with charged kaons in three-prong τ decays are studied by exploiting the particle identification from the dE/dx measurement. The results are based on a sample of about 1.6 × 105 detected τ pairs collected with the ALEPH detector between 1991 and 1995 around the Z peak. The following branching ratios have been measured: B(τ- → K−K+π−ντ) = (1.63 ± 0.21 ± 0.17) × 10−3, B(τ− → K−π+π−ντ) = (2.14 ± 0.37 ± 0.29) × 10−3, B(τ− → K−K+π−π0ντ) = (0.75 ± 0.29 ± 0.15) × 10−3, and B(τ− → K−π+π−π0ντ) = (0.61 ± 0.39 ± 0.18) × 10−3. The first two measurements are more precise than the current world averages, while the last two channels are investigated for the first time. The 95% C.L. upper limit on the branching ratio for the decay τ− → K−K+K−ντ is 0.19 × 10−3. A study of intermediate states occurring in the K−K+π−ντ and K−π+π−ντ decays is also presented.

Inclusive π±, K± and (p, p̄) production is investigated using data recorded by the ALEPH detector between 1992 and 1994. The momentum spectra and multiplicities are measured separately in Z → bb̄, Z → cc̄ and Z → uū, dd̄, ss̄ decays. The number of protons found in b-hadron decays is used to estimate the fraction of b-baryons in b events to be (10.2 ± 0.7 ± 2.7)% assuming BR(b-baryon→ pX) = (58 ± 6)%. From an additional study of proton-lepton correlations in b events, the branching ratio BR(b-baryon → plv̄X) = (4.63 ± 0.72 ± 0.98)% is obtained. The ratio BR(b-baryon → plv̄X)/BR(b-baryon → pX) is found to be 0.080 ± 0.012 ± 0.014.

The 132 pbt - 1 of data collected by ALEPH from 1991 to 1994 have been used to analyze η and ω production in τ decays. The following branching fractions have been measured: \(B\left( {{\tau ^ - } \to {\nu _\tau }\omega {h^ - }} \right) = \left( {1.91 \pm 0.07 \pm 0.06} \right) \times {10^{ - 2}},\) \(B\left( {{\tau ^ - } \to {\nu _\tau }\omega {h^ - }{\pi ^0}} \right) = \left( {4.3 \pm 0.6 \pm 0.5} \right) \times {10^{ - 3}},\) \(B\left( {{\tau ^ - } \to {\nu _\tau }\eta {K^ - }} \right) = \left( {2.9_{ - 1.2}^{ + 1.3} \pm 0.7} \right) \times {10^{ - 4}},\) \(B\left( {{\tau ^ - } \to {\nu _\tau }\eta {h^ - }{\pi ^0}} \right) = \left( {1.8 \pm 0.4 \pm 0.2} \right) \times {10^{ - 3}}\) and the 95% C.L. limit B(τ− → ντηπt -) < 6.2 × 10t - 4 has been obtained. The ωπt- and ηπt -π0 rates and dynamics are found in agreement with the predictions made from e+e∼ - annihilation data with the help of isospin invariance (CVC).

The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb−1. An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c 2. The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses.

The lifetimes of theB 0 andB + mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB 0 andB + mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− or$$\bar D^0 $$ meson. The second method used fully reconstructedB 0 andB + mesons. The third method, used to measure theB 0 lifetime, employed a partial reconstruction technique to identifyB 0→D*− π + X decays. The combined results are $$\begin{gathered} \tau _0 = 1.55 \pm 0.06 \pm 0.03 ps, \hfill \\ \tau _ + = 1.58 \pm 0.09 \pm 0.03 ps, \hfill \\ \tfrac{{\tau _ + }}{{\tau _0 }} = 1.03 \pm 0.08 \pm 0.02. \hfill \\ \end{gathered} $$ .