From 1.4 million hadronic Z decays collected by the ALEPH detector at LEP, an enriched sample of Z → cc̄ events is extracted by requiring the presence of a high momentum D ∗± . The charm quark forward-backward charge asymmetry at the Z pole is measured to be A FB 0. c = (8.0 ± 2.4) % corresponding to an effective electroweak mixing angle of sin 2 θ W eff = 0.2302 ± 0.0054.
Value of SIN2TW(eff) from CQ-quark asymmetries.
No description provided.
The production rates of D*+-, Ds*+-, D+-, D0 / D0bar, Ds+, and Lambda_c in Z to ccbar decays are measured using the LEP I data sample recorded by the ALEPH detector. The fractional energy spectrum of the D*+- is well described as the sum of three contributions: charm hadronisation, b hadron decays and gluon splitting into a pair of heavy quarks. The probability for a c quark to hadronise into a D*+ is found to be f(c to D*+) = 0.233 +- 0.010 (stat.) +- 0.011 (syst.). The average fraction of the beam energy carried by D*+- mesons in Z to cc events is measured to be < X_E (D*+-) >_cc = 0.4878 +- 0.0046 (stat.) +- 0.0061 (syst.). The D*+- energy and the hemisphere mass imbalance distributions are simultaneously used to measure the fraction of hadronic Z decays in which a gluon splits to a cc pair: n_{gluon to cc} = (3.23 +- 0.48 (stat.) +- 0.53 (syst.) %. The ratio of the Vector/(Vector+Pseudoscalar) production rates in charmed mesons is found to be P_V = 0.595 +- 0.045. The fractional decay width of the Z into cc pairs is determined from the sum of the production rates for various weakly decaying charmed states to be Rc = 0.1738 +- 0.0047 (stat.) +- 0.0116 (syst.).
The multiplicity of D*+- events using a MC shape to do the very small extrapolation over the entire X range.
Fraction of hadronic Z0 decays into charm quark pairs summing all the contributions of the fundamental charmed states and including a contribution from baryons not decaying to LAMBDA/C+. The second DSYS error is due to the uncertainty in the branching ratio.
The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.
Differential cross section as a function of the relative energy of the scattered electrons.
Differential cross section as a function of the polar angle THETA of the scattered electrons.
Differential cross section as a function of the virtuality Q**2 of the photons.
The inclusive production of D$^{*\pm}$ mesons in two-photon collisions is measured with the ALEPH detector at $\epem$ centre-of-mass energies from 183$\unit{GeV}$ to 209$\unit{GeV}$. A total of $360 \pm 27$ D$^{*\pm}$ meson events were observed from an integrated luminosity of 699\unit{pb^{-1}}$. Contributions from direct and single-resolved rocesses are separated using the ratio of the transverse momentum $p_{\rm t}^{\rm D^{*\pm}}$ of the D$^{*\pm}$ to the visible invariant mass $W_{\mathrm{vis}}$ of the event. Differential cross sections of D$^{*\pm}$ production as functions of $p_{\rm t}^{\rm D^{*\pm}}$ and the pseudorapidity $|\eta^{\rm D^{*\pm}}| $ are measured in the range $ 2\unit{GeV}/c < p_{\rm t}^{\rm D^{*\pm}} < 12\unit{GeV}/c $ and $ |\eta^{\rm D^{*\pm}}| < 1.5 $. They are compared to next-to-leading order (NLO)perturbative QCD calculations. The extrapolation of the integrated visible D$^{*\pm}$ cross section to the total charm cross section, based on the Pythia Monte Carlo program, yields $ \sigma (\epem \to \epem \ccbar)_ {=197\unit{GeV}} = 731 \pm 74_{\mathrm{stat}} \pm 47_{\mathrm{syst}} \pm 157_{\mathrm{extr}} \unit{pb} $.
Total extrapolated charm production cross section. The second DSYS error isdue to the uncertainty in the extrapolation.
Visible cross section with the acceptance range.
Visible cross section within the acceptance ranges for the three decay modes observed.
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.
Charged particle multiplicity distributions have been measured with the ALEPH detector in restricted rapidity intervals |Y| ≤0.5, 1.0, 1.5, 2.0 along the thrust axis and also without restriction on rapidity. The distribution for the full range can be parametrized by a log-normal distribution. For smaller windows one finds a more complicated structure, which is understood to arise from perturbative effects. The negative-binomial distribution fails to describe the data both with and without the restriction on rapidity. The JETSET model is found to describe all aspects of the data while the width predicted by HERWIG is in significant disagreement.
Unfolded charged particle multiplicity distribution given the probability to have an hadronic Z0 decay with MULT charged particles.
Unfolded multiplicity distributions for restricted rapidity bin <= 0.5 along the thrust axis.
Unfolded multiplicity distributions for restricted rapidity bin <= 1.0 along the thrust axis.
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.
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.
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.
Cross section for the process E+ E- --> E+ E- BQUARK BQUARKBAR X.
The inclusive production of the omega(782) vector meson in hadronic Z decays is measured and compared to model predictions. The analysis is based on 4 million hadronic Z decays recorded by the ALEPH detector between 1991 and 1995. The production rate for x_p = p_meson/p_beam > 0.05 is measured in the omega -> pi^+ pi^- pi^0 decay mode and found to be 0.585 +- 0.019_stat +- 0.033_sys per event. Inclusive eta meson production is also measured in the same decay channel for x_p > 0.10, obtaining 0.355 +- 0.011_stat +- 0.024_sys per event. The branching ratio for omega -> mu^+ mu^- is investigated. A total of 18.1 +- 5.9 events are observed, from which the muonic branching ratio is measured for the first time to be BR(omega -> mu^+ mu^-) = (9.0 +- 2.9_stat +- 1.1_sys)*10^-5.
Extrapolation using JETSET 7.4 is used to correct down to X = 0.0. The second DSYS error, where relevant, shows the estimated uncertainty on the extrapolation.
Production rate and differential cross sections for the ETA.
Production rate and differential cross sections for the OMEGA.
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