Study of the fragmentation of b quarks into B mesons at the Z peak

The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991-1995. A semi-exclusive reconstruction of B->l nu D(*) decays is performed, by combining lepton candidates with fully reconstructed D(*) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xewd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be mxewd = 0.716 +- 0.006 (stat) +- 0.006 (syst) using a model-independent method; the corresponding value for the energy of the leading B meson is mxel = 0.736 +- 0.006 (stat) +- 0.006 (syst). The reconstructed spectra …

Two-dimensional analysis of Bose-Einstein correlations in hadronic Z decays at LEP

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.

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

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

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.

Search for Single Top Production in $e^{+} e^{-}$ Collisions at $\sqrt{s}$ up to 209 GeV

Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c, \bar{t}u is searched for within the 214 pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> ��c)+BR(t -> ��u)= 0 and mt=174 GeV/c2.

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…