The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> pi+ pi-. From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%. They are used to measure the CP asymmetry of this decay, given by sin 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%.
Standard Model predicts the time-dependent rate asymmetry as follows: A(t) = (B0(t)-BBAR0(t))/(B0(t)+BBAR0(t)) = SIN(2*BETA)*SIN(Delta(M)*t), where Delta(M) is the mass difference between the two B0 mass eigenstates.
Hadronic Z decay data taken with the ALEPH detector at LEP1 are used to measure the three-jet rate as well as moments of various event-shape variables. The ratios of the observables obtained from b-tagged events and from an inclusive sample are determined. The mass of the b quark is extracted from a fit to the measured ratios using a next-to-leading order prediction including mass effects. Taking the first moment of the y3 distribution, which is the observable with the smallest hadronization corrections and systematic uncertainties, the result is: mb(MZ) = [3.27+-0.22(stat) +-0.22(exp)+-0.38(had)+-0.16(theo)] GeV/c2. The measured ratio is alternatively employed to test the flavour independence of the strong coupling constant for b and light quarks.
No description provided.
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.
An analysis of global event-shape variables has been carried out for the reaction e + e − →Z 0 →hadrons to measure the strong coupling constant α s . This study is based on 52 720 hadronic events obtained in 1989/90 with the ALEPH detector at the LEP collider at energies near the peak of the Z-resonance. In order to determine α s , second order QCD predictions modified by effects of perturbative higher orders and hadronization were fitted to the experimental distributions of event-shape variables. From a detailed analysis of the theoretical uncertainties we find that this approach is best justified for the differential two-jet rate, from which we obtain α s ( M Z 2 ) = 0.121 ± 0.002(stat.)±0.003(sys.)±0.007(theor.) using a renormalization scale ω = 1 2 M Z . The dependence of α s ( M Z 2 ) on ω is parameterized. For scales m b <ω< M Z the result varies by −0.012 +0.007 .
The second DSYS error is the theoretical error.
Distributions are presented of event shape variables, jet roduction rates and charged particle momenta obtained from 53 000 hadronicZ decays. They are compared to the predictions of the QCD+hadronization models JETSET, ARIADNE and HERWIG, and are used to optimize several model parameters. The JETSET and ARIADNE coherent parton shower (PS) models with running αs and string fragmentation yield the best description of the data. The HERWIG parton shower model with cluster fragmentation fits the data less well. The data are in better agreement with JETSET PS than with JETSETO(αS2) matrix elements (ME) even when the renormalization scale is optimized.
Sphericity distribution.
Sphericity distribution.
Aplanarity distribution.
None
Three different methods are used for extraction Alphas value (see text for details). Systematical errors with C=HADR and C=THEOR are due to hadronization correction and theoretical uncertainties.
Using about 950000 hadronic events collected during 1991 and 1992 with the ALEPH detector, the ratios r b = α s b α s udsc and r uds = α s uds α s cb have been measured in order to test the flavour independence of the strong coupling constant α s . The analysis is based on event-shape variables using the full hadronic sample, two b -quark samples enriched by lepton tagging and lifetime tagging, and a light-quark sample enriched by lifetime antitagging. The combined results are r b = 1.002±0.023 and r uds = 0.971 ± 0.023.
No description provided.
None
NC, CF, and TF are the color factors for SU(N) group. For SU(3) they are equal to: NC = 3, CF = 4/3, and TF = 1/2.
Quark and gluon jets with the same energy, 24 GeV, are compared in symmetric three-jet configurations from hadronic Z decays observed by the ALEPH detector. Jets are defined using the Durham algorithm. Gluon jets are identified using an anti-tag on b jets, based on a track impact parameter method. The comparison of gluon and mixed flavour quark jets shows that gluon jets have a softer fragmentation function, a larger angular width and a higher particle multiplicity, Evidence is presented which shows that the corresponding differences between gluon and b jets are significantly smaller. In a statistically limited comparison the multiplicity in c jets was found to be comparable with that observed for the jets of mixed quark flavour.
B-jets are identified with the lepton-tag analysis.
The same kinematics as in the table 1.
The production rates and the inclusive cross sections of the isovector meson${\rm \pi^0}$, the isoscalar mesons$\eta$and
Inclusive cross section for PI0 production in hadronic events.
Inclusive cross section for ETA production in hadronic events.
Inclusive cross section for ETAPRIME production in hadronic events.
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