Measurement of Ab_FB using inclusive b-hadron decays

Based on a sample of four million events collected by ALEPH from 1991 to 1995, a measurement of the forward-backward asymmetry in Z -> b-barb decays using inclusive final states is presented. High-performance tagging of b-barb events in a wide angular range is achieved using neural network techniques. An optimal hemisphere charge estimator is built by merging primary and secondary vertex information, leading kaon identification and jet charge in a neural network. The average charge asymmetry, the flavour tagging efficiencies and mean b-hemisphere charges are measured from data and used to extract the pole b asymmetry in the Standard Model A^{0,b}_{FB} = 0.1009 +- 0.0027 (stat) +- 0.0015 …

Single vector boson production in e(+)e(-) collisions at centre-of-mass energies from 183 to 209 GeV

The cross sections for single vector boson production in the Wenu and Zee channels are measured from the data collected by AA the ALEPH detector at LEP for centre-of-mass energies between 183 and 209 GeV. These data correspond to a total integrated luminosity of 683 pb(-1). Single-W production is studied in both hadronic and leptonic decay channels. Hadronic and dimuon decays are used for single-Z production. The measured cross sections agree with the Standard Model predictions.

Search for scalar leptons in e+e- collisions at centre-of-mass energies up to 209 GeV

A search for selectron, smuon and stau pair production is performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies up to 209 GeV. The numbers of candidate events are consistent with the background predicted by the Standard Model. Final mass limits from ALEPH are reported.

Test of Colour Reconnection Models using Three-Jet Events in Hadronic Z Decays

Hadronic Z decays into three jets are used to test QCD models of colour reconnection (CR). A sensitive quantity is the rate of gluon jets with a gap in the particle rapidity distribution and zero jet charge. Gluon jets are identified by either energy-ordering or by tagging two b-jets. The rates predicted by two string-based tunable CR models, one implemented in JETSET (the GAL model), the other in ARIADNE, are too high and disfavoured by the data, whereas the rates from the corresponding non-CR standard versions of these generators are too low. The data can be described by the GAL model assuming a small value for the R_0 parameter in the range 0.01-0.02.

Measurement of the cross section for open b-quark production in two-photon interactions at LEP

The topology dependence of charged particle multiplicities in three-jet events

A study of individual jet and whole-event charged particle multiplicities in three-jet events measured in e(+)e(-) annihilation at the Z reveals a significant topology dependence. Mean jet multiplicities are inadequately described by jet energies; interjet angles must also be specified. Quantitative tests suggest that it is necessary to use transverse-momentum-like scales to describe the data. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

Deuteron and anti-deuteron production in e+ e- collisions at the Z resonance

Deuteron and anti-deuteron production in Z decays has been observed in the ALEPH experiment at LEP. The production rate of anti-deuterons is measured to be per hadronic Z decay in the anti-deuteron momentum range from 0.62 to 1.03 GeV/c. The coalescence parameter , which characterizes the likelihood of anti-deuteron production, is measured to be in Z decays. These measurements indicate that the production of anti-deuterons is suppressed in collisions compared to that in pp and photoproduction collisions

Measurement of the W boson Mass and Width in $e^{+}e^{-}$ Collisions at LEP

The mass of the W boson is determined from the direct reconstruction of W decays in WW→qq̄qq̄ and WW→ℓνqq̄ events in e+e- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 pb-1 collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection a new procedure is adopted in which low energy particles are not considered in the mass determination from the qq̄qq̄ channel. The combined result from all channels is mW=80.440±0.043(stat.)±0.024(syst.)±0.009(FSI)±0.009(LEP)GeV/c2,where FSI represents the possible effects of final state interactions in the qq̄qq̄ channel and LEP indicates the uncertainty in the b…

Measurement of the Michel parameters and the nu(tau) helicity in tau lepton decays

A measurement of the Michel parameters and the average $\nu_\tau$ helicity in $\tau$ 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\,$\text{pb}^{-1}$ is analysed. The Michel parameters $\rho_l$, $\xi_l$, $(\xi\delta)_l$ ($l=e,\mu$), and $\eta_\mu$ are determined for the leptonic deca ys, and the chirality parameters $\xi_\pi$, $\xi_\rho$, and $\xi_{a_1}$ for the hadronic final states. Under the assumptions of $e$\bis $\mu$ universality and $\xi_\pi=\xi_\rho=\xi_{a_1}$, the values $\rho_l=0.742\pm 0.016, \eta_l=0.01 2\pm 0.026,\break (\xi\delta)_l=0.776\pm 0.051, \xi_l=0.986\pm 0.074$, and …

A measurement of Rb using mutually exclusive tags

A measurement of R-b using five mutually exclusive hemisphere tags has been performed by ALEPH using the full LEP1 statistics. Three tags are designed to select the decay of the Z(0) to b quarks, while the remaining two select Z(0) decays to c and light quarks, and are used to measure the tagging efficiencies. The result, R-b = 0.2159 +/- 0.0009(stat) +/-0.0011(syst), is in agreement with the electroweak theory prediction of 0.2158 +/- 0.0003. (C) 1997 Published by Elsevier Science B.V. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Forti, Francesco/H-3035-2011; Ferrante, Isidoro/F-1017-2012

Two-particle correlations in pp, (p)over-bar(p)over-bar and (KSKS0)-K-0 pairs from hadronic Z decays

Two-particle correlations in pp, and pairs have been studied in hadronic Z decays recorded at LEP with the ALEPH detector. The correlations were measured as a function of the four-momentum difference Q of the pair. For pp, pairs a depletion of events is observed in the region , and for pairs an enhancement of events is observed in the region . These features are consistent with expectations from Fermi–Dirac and Bose–Einstein statistics, respectively.

A measurement of the QCD colour factors and a limit on the light gluino

Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios C-A/C-F and T-F/C-F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD. C-A/C-F = 2.20 +/- 0.09 (stat) +/- 0.13 (syst), T-F/C-F = 0.29 +/- 0.05 (stat) +/- 0.06 (syst). Fixing C-A/C-F and T-F/C-F to the QCD values permits a determination of alpha(s) (M-Z) and n(f), the number of active flavours. With this measurement the existence of a gluino with mass below …

Bose-Einstein correlations in W-pair decays with an event-mixing technique

Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW→qq̄qq̄ events to "mixed" events constructed with the hadronic part of WW→qq̄ℓν events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured.

Improved measurement of the triple gauge-boson couplings gamma WW and ZWW in e(+)e(-) collisions

Triple gauge-boson couplings ?WW and ZWW involving single-photon, single-W and W-pair production are determined using data samples collected at LEP with the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. The integrated luminosity used is 700 pb-1 for the single-photon measurement and 683 pb-1 for the W channels. Restricting the measurement to C- and P-conserving terms and applying local SU(2) L×U(1)Y gauge invariance, the measured values of the parameters g1 Z, ?? and ?? are: g1 Z=1.001±0. 027(stat)±0.013(syst), ??=0.971±0.055(stat) ±0.030(syst), ??=-0.012±0.027(stat) ±0.011(syst) for single-parameter fits, where the two other parameters are fixed to their Standard Model…