Based on 520 000 fermion pairs accumulated during the first three years of data collection by the ALEPH detector at LEP, updated values of the resonance parameters of theZ are determined to beMZ=(91.187±0.009) GeV, ΓZ=(2.501±0.012) GeV, σhad0=(41.60±0.27) nb, andRℓ=20.78±0.13. The corresponding number of light neutrino species isNν=2.97±0.05. The forward-backward asymmetry in lepton-pair decays is used to determine the ratio of vector to axial-vector couplings of leptons:gV2(MZ2)/gA2(MZ2)=0.0052±0.0016. Combining this with ALEPH measurements of theb andc quark asymmetries and τ polarization gives sin2θWeff=0.2326±0.0013. Assuming the minimal Standard Model, and including measurements ofMW/MZ fromp\(\bar p\) colliders and neutrino-nucleon scattering, the mass of the top quark is\(M_{top} = 156 \pm \begin{array}{*{20}c} {22} \\ {25} \\ \end{array} \pm \begin{array}{*{20}c} {17} \\ {22Higgs} \\ \end{array} \) GeV.
Data for 1991 running period.
Data for 1991 running period.
Data for 1991 running period.
The differential cross sections for lepton pair production in e+e− annihilation at 29 GeV have been measured and found to be in good agreement with the standard model of the electroweak interaction. With the assumption of e−μ−τ universality, the weak neutral-current couplings are determined to be ga2=0.23±0.05 and gv2=0.03±0.04.
Extrapolated to full angular range.
Extrapolated to full angular range.
EXTRAPOLATION TO TOTAL SOLID ANGLE.
Data of the ηπ − system were obtained in the reaction π − p → ηπ − p at 6.3 GeV/ c beam momentum. About 17 k events of ηπ − were collected in the mass range 0.8 ⩽ M ηπ - ⩽ 1.8 GeV/ c 2 and in the range of the momentum transfer squared 0.075 ⩽ | t ′| ⩽ 0.60 (GeV/ c ) 2 . A large forward-backward asymmetry was observed around 1.3 GeV/ c 2 in the Gottfried-Jackson frame of the ηπ − system. A partial wave analysis of the data was performed. A peak of the D + wave attributed to a 2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/ c 2 in the P + wave.
No description provided.
We present asymmetries between the production of D+ and D- mesons in Fermilab experiment E791 as a function of xF and pt**2. The data used here consist of 74,000 fully-reconstructed charmed mesons produced by a 500 GeV/c pi- beam on C and Pt foils. The measurements are compared to results of models which predict differences between the production of heavy-quark mesons that have a light quark in common with the beam (leading particles) and those that do not (non-leading particles). While the default models do not agree with our data, we can reach agreement with one of them, PYTHIA, by making a limited number of changes to parameters used.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of Feynman variable X. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
Asymmetry parameter A = (SIG(D-)-SIG(D+))/(SIG(D+)+SIG(D-)) have been studied as function of PT**2. 'Nucleus' are PT and C.
We report on a study of inclusive production ofD*± mesons ine+e− annihilation at c.m. energies between 28 and 46.8 GeV using the TASSO detector at the PETRA storage ring. A hardD*± energy spectrum is measured with a maximum nearED*±≃0.6Ebeam. The measured cross section ratio\((\sigma _{D^{* + } }+ \sigma _{D^{* - } } )/\sigma _{\mu \mu }= 1.28 \pm 0.09 \pm 0.18\) indicates thatD* production accounts for a large fraction of the observed charm production. Two complementary methods have been used to determine the forward-backward asymmetry of charm pair production due to electroweak interference. Combining both measurements the product of the axial vector couplings of the electron and the charm quark to the weak neutral current was determined to begAegAc=−(0.276±0.073), in agreement with the standard model prediction of −0.25. Using a sample of reconstructedD*± mesons, the relative strength of the strong interaction coupling of thec quark compared to that of an average of all flavours is measured as αs(c)/αs(all)=0.91±0.38±0.15, consistent with the coupling constant being flavour independent. An update of ourD0 lifetime measurement is presented, based on a considerable increase in statistics, the final result being\(\tau _{D^0= } (4.8 \pm _{0.9 - 0.7}^{1.0 + 0.5} )10^{ - 13} s\).
Measurement of the charm quark production asymmetry using reconstructed D* mesons.
Measurement of the charm quark production asymmetry using an independent method based on the measurement of the direction of low PT pions.
This paper presents measurements of the production of Ds- mesons relative to Ds+ mesons as functions of x_F and square of p_t for a sample of 2445 Ds decays to phi pi. The Ds mesons were produced in Fermilab experiment E791 with 500 GeV/c pi- mesons incident on one platinum and four carbon foil targets. The acceptance-corrected integrated asymmetry in the x_F range -0.1 to 0.5 for Ds+- mesons is 0.032 +- 0.022 +- 0.022, consistent with no net asymmetry. The results, as functions of x_F and square of p_t, are compared to predictions and to the large production asymmetry observed for D+- mesons in the same experiment. These comparisons support the hypothesis that production asymmetries come from the fragmentation process and not from the charm quark production itself.
No description provided.
No description provided.
No description provided.
A high-statistics measurement is presented of the cross section for the process e+e−→τ+τ− at s=29 GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with |cosθ|<0.9 gives an asymmetry Aττ=−0.055±0.012±0.005 from which we find the product of electron and tau axial-vector weak neutral couplings gAegAτ=0.22±0.05.
Data extrapolated to full acceptance.
No description provided.
We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected
Results from 1990 data. Additional systematic uncertainty of 0.005.. Acollinearity required to be <15 degrees.
Results from 1991 data. Additional systematic uncertainty of 0.002.. Acollinearity required to be <15 degrees.
Results from 1992 data. Additional systematic uncertainty of 0.002.. Acollinearity required to be <15 degrees.
We report the first measurement of the longitudinal double-spin asymmetry $A_{LL}$ for mid-rapidity di-jet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s} = 200$ GeV. The di-jet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. $A_{LL}$ results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-$x > 0.05$.
Di-jet A_LL asymmetry vs parton-level invariant mass for the same-sign di-jet topology. The systematic uncertainty on the mass includes contributions from jet energy scale, the correction to parton-level, and the difference between NLO and PYTHIA cross sections. The systematic uncertainty on the asymmetry includes contributions from trigger and reconstruction bias and residual transverse beam polarization components. A 6.5% uncertainty common to all points due to uncertainty on the measured beam polarizations is also present, but not included in the uncertainties quoted below.
Theoretical predictions for the di-jet A_LL asymmetry for the same-sign topology using the DSSV14 and NNPDFpol1.1 polarized PDF sets. The DSSV14 prediction is presented without uncertainty while the systematic uncertainty on the NNPDFpol1.1 prediction contains contributions from factorization and renormalization scale uncertainties and PDF uncertainties.
Di-jet A_LL asymmetry vs parton-level invariant mass for the opposite-sign di-jet topology. The systematic uncertainty on the mass includes contributions from jet energy scale, the correction to parton-level, and the difference between NLO and PYTHIA cross sections. The systematic uncertainty on the asymmetry includes contributions from trigger and reconstruction bias and residual transverse beam polarization components. A 6.5% uncertainty common to all points due to uncertainty on the measured beam polarizations is also present, but not included in the uncertainties quoted below.
We report on the properties of theZ resonance from 62 500Z decays into fermion pairs collected with the ALEPH detector at LEP, the Large Electron-Positron storage ring at CERN. We findMZ=(91.193±0.016exp±0.030LEP) GeV, ΓZ=(2497±31) MeV, σhad0=(41.86±0.66)nb, and for the partial widths Γinv=(489±24) MeV, Γhad(1754±27) MeV, Γee=(85.0±1.6)MeV, Γμμ=(80.0±2.5) MeV, and Γττ=(81.3±2.5) MeV, all in good agreement with the Standard Model. Assuming lepton universality and using a lepton sample without distinction of the final state we measure Γu=(84.3±1.3) MeV. The forward-backward asymmetry in leptonic decays is used to determine the vector and axial-vector weak coupling constants of leptors,gv2(MZ2)=(0.12±0.12)×10−2 andgA2(MZ2)=0.2528±0.0040. The number of light neutrino species isNν=2.91±0.13; the electroweak mixing angle is sin2θW(MZ2)=0.2291±0.0040.
No description provided.
No description provided.
No description provided.
Forum