A measurement of the spectral functions of non-strange τ vector current final states is presented, using 124 358 τ pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two- and four-pion τ decay channels are compared to published results of e+e- annihilation experiments via isospin rotation. A combined fit of the pion form factor from τ decays and e+e- data is performed using different parametrizations. The mass and the width of the ρ±(770) and the ρ0(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be Mρ±(770) - Mρ0(770) = (0.0 ± 1.0) MeV/c2 and Γρ±(770) - Γρ0(770) = (0.1 ± 1.9) MeV/c2.
Invariant mass-squared distribution of the $\tau^- \to h^- \pi^0 \nu_{\tau}$ decay. The error has been set to zero if it is smaller than the point size. A dash indicates a data point lying outside the plot range.
Invariant mass-squared distributions of the $h^- 3\pi^0 \nu_{\tau}$ decay channel. The error has been set to zero if it is smaller than the point size.
Invariant mass-squared distribution of the $2h^- h^+ \pi^0 \nu_{\tau}$ decay channel. The error has been set to zero if it is smaller than the point size.
Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios CA/CF and TF /CF and the strong coupling constant αs = CFαs(MZ)/(2π) 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, {fx4-1} Fixing CA/CF and TF/CF to the QCD values permits a determination of αs(MZ) and ηf, the number of active flavours. With this measurement the existence of a gluino with mass below 6.3 GeV/c2 is excluded at 95% confidence level.
Fit A: using all kinematical distributions. NC, CF, and TF are the color factors for SU(3) group, NF is the number of the active flavors.
Fit B: using all kinematical distributions, but QCD magnitudes for color factors are used: FA(DEF=NC/CF)) = 2.25 and TF/CF = 0.375. NC, CF, and TF are the color factors for SU(3) group, NF is the number of the active flavors.
Fit C: the QCD magnitudes for color factors and NF = 5 are used.
Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.
Charged particle sphericity distribution.
Charged particle aplanarity distribution.
Charged particle Thrust distribution.
A measurement of the inclusive production of π0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of ⊡s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive π0 momentum spectrum is measured in the range 0.025 < xp = p/pbeam < 1. In this range the number of π0 per hadronic Z is found to be 4.80 ± 0.07(stat) ± 0.31(sys). The differential inclusive π0 cross section is also measured as a function of transverse momentum with respect to the event plane (pTin and pTout).
PI0 multiplicity and cross sections for events with two converted photons.
PI0 multiplicity and cross sections for events with only one converted photon. Final data point for full x range uses jetset 7.4 monte carlo extrapolation prediction.
PI0 cross sections as a function of the transverse momentum PTOUT relative to the plane defined by the sphericity tensor.
Two samples of exclusive semileptonic decays, 579 B 0 → D ∗+ ℓ − ν ℓ events and 261 B 0 → D + ℓ − ν ℓ events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F (ω) at zero recoil of the D (∗)+ meson and the CKM matrix element | V cb | are measured to be F D ∗+ (1)|V cb | = (31.9 ± 1.8 stat ± 1.9 syst ) × 10 −3 , F D + (1)| V cb | = (27.8 ± 6.8 stat ± 6.5 syst ) × 10 −3 . The ratio of the form factors F D + (1) and F D ∗+ (1) is measured to be F D + (1) F D ∗+ (1) = 0.87 ± 0.22 stat ± 0.21 syst . A value of | V cb | is extracted from the two samples, using theoretical constraints on the slope and curvature of the hadronic form factors and their normalization at zero recoil, with the result | V cb | = (34.4 ± 1.6 stat ± 2.3 syst ± 1.4 th ) × 10 −3 . The branching fractions are measured from the two integrated spectra to be Br ( B 0 → D ∗+ ℓ − ν ℓ ) = (5.53 ± 0.26 stat ±0.52 syst ) %, Br ( B 0 → D ∗+ ℓ − ν ℓ ) = (2.35 ± 0.20 stat ± 0.44 syst ) %.
The formfactors are evaluated at zero recoil of D meson. Two different methods are used (see text for details). VCB is the KCM matrix element. The formfactor fitted to dependence: FF(OM) = FF(1)*(1-CONST*(OM-1)).
VCB is the KCM matrix element.
VCB is the KCM matrix element.
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).
$\pi^+\pi^-\pi^0$ mass distribution (two entries per event) in the $\pi^{\pm}\pi^+\pi^-\pi^0$ final state for the one-photon sample. The bin size has been chosen to display the detailed shape of the $\omega$ peak. The non-resonant contribution is represented by a simple polynomial. Non-$\tau$ background has been subtracted. The error has been set to zero if it is smaller than the point size.
$\pi^+\pi^-\pi^0$ mass distributions (two entries per event) in the $\pi^{\pm}\pi^+\pi^-\pi^0$ final state for the two-photon sample. The bin size has been chosen to display the detailed shape of the $\omega$ peak. The non-resonant contribution is represented by a simple polynomial. Non-$\tau$ background has been subtracted. The error has been set to zero if it is smaller than the point size.
Background-subtracted $\omega\pi$ mass spectrum for the data presented here, plotted as black dots. The error has been set to zero if it is smaller than the point size.
The B<sup loc="post">0</sup> - B̄<sup loc="post">0</sup> average mixing parameter <math altimg="si1.gif"><rm><ovl type="bar" style="s">χ</ovl></rm></math> and b forward-backward asymmetry AFB<sup loc="post">0</sup>(b) are measured from a sample of about 4 200 000 Z → qq̄ events recorded with the ALEPH detector at LEP in the years 1990–1995. High transverse momentum electrons and muons produced in b semileptonic decays provide the tag of the quark flavour and of its charge. The average mixing parameter and the pole b asymmetry are measured to be <math altimg="si1.gif"><rm><ovl type="bar" style="s">χ</ovl></rm></math> = 0.1246 ± 0.0051stat ± 0.0052syst, AFB<sup loc="post">0</sup>(b) = 0.1008 ± 0.0043stat ± 0.0028syst. The value of sin<sup loc="post">2</sup>θw<sup loc="post">eff</sup> = 0.23198 ± 0.00092 is extracted from the asymmetry measurement.
ASYM(N=FB,C=OBSERVED) is observed asymmetry including BQ, CQ and backround.
No description provided.
A lower limit on the oscillation frequency of the B s 0 B s 0 system is obtained from approximately four million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1995. Leptons are combined with opposite sign D s − candidates reconstructed in seven different decay modes as evidence of semileptonic B s 0 decays. Criteria designed to ensure precise proper time reconstruction select 277D s − ℓ + combinations. The initial state of these B s 0 candidates is determined using an algorithm optimized to efficiently utilise the tagging information available for each event. The limit at 95% confidence level on the B s 0 B s 0 oscillation frequency is Δm s > 6.6 ps −1 . The same data is used to update the measurement of the B s 0 lifetime, τ s = 1.54 −0.13 +0.14 (stat) ± 0.04 (syst) ps.
This result supersedes the previous measurement ( 1.59 +0.17 -0.15 (stat.) +-0.03 (sys.) ps ) presented in reference PL 361B, 221.
No description provided.
The polarization of Λ baryons from Z decays is studied with the Aleph apparatus. Evidence of longitudinal polarization of s quarks from Z decay is observed for the first time. The measured longitudinal Λ polarization is P L Λ = −0.32 ± 0.07 for z = p p beam > 0.3 . This agrees with the prediction of −0.39 ± 0.08 from the standard model and the constituent quark model, where the error is due to uncertainties in the mechanism for Λ production. The observed Λ polarization is diluted with respect to the primary s quark polarization by Λ baryons without a primary s quark. Measurements of the Λ forward-backward asymmetry and of the correlation between back-to-back Λ Λ pairs are used to check this dilution. In addition the transverse Λ polarization is measured. An indication of transverse polarization, more than two standard deviations away from zero, is found along the normal to the plane defined by the thrust axis and the Λ direction.
No description provided.
No description provided.
No description provided.
None
The first sytematic error is due to the experimental uncertainties, whilst the second is due to the uncertainties in the quark charge separations.
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