We have determined the strong coupling αs from measurements of jet rates in hadronic decays of Z0 bosons collected by the SLD experiment at SLAC. Using six collinear and infrared safe jet algorithms we compared our data with the predictions of QCD calculated up to second order in perturbation theory, and also with resummed calculations. We find αs(MZ2)=0.118±0.002(stat)±0.003(syst)±0.010(theory), where the dominant uncertainty is from uncalculated higher order contributions.
The second systematic error comes from the theoretical uncertainties.
We measure the Drell-Yan differential cross section d2σdMdy||y|<1 over the mass range 11
Dielectron differential cross section.
Dimuon differential cross section.
Drell-Yan differential cross section for combined dielectron and dimuon data. Error includes both statistics and systematics.
The forward-backward asymmetries of$$e^ + e^ - \to Z^0 \to b\bar b and e^ + e^ - \to Z^0 \to c\bar c$$
Measurement of the asymmetry in b-quark production on the Z0 peak using a two parameter fit, neglecting the effects of B0-BBAR0 mixing.
Measurement of the asymmetry in b-quark production on the Z0 peak using a two parameter fit and correcting for B0-BBAR0 mixing. The second systematic error is due to the uncertainty of the mixing factor.
Measurement of the asymmetry in c-quark production on the Z0 peak using a two parameter fit.
A study of the fragmentation properties of charm and bottom quarks intoD mesons is presented. From 263 700Z0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider,D0,D+ andD*+ are reconstructed in the modesK−π+,K−π+K+ andD0π+ followed byD0→K−π+, respectively. The fractional decay widths\(\Gamma {{(Z^0\to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} \mathord{\left/ {\vphantom {{(Z^0\to {D \mathord{\left/ {\vphantom {D {\bar D}}} \right. \kern-\nulldelimiterspace} {\bar D}}X)} {\Gamma _h }}} \right. \kern-\nulldelimiterspace} {\Gamma _h }}\) are determined, and first results are presented for the production ofD mesons from\(c\bar c\) and\(b\bar b\) events separately. The average energy fraction ofD*± in charm quark fragmentation is found to be 〈XE(D*)〉c=0.487±0.015 (stat)±0.005 (sys.). Assuming that the fraction ofDs and charm-baryons produced at LEP is similar to that around 10 GeV, theZ0 partial width into charm quark pairs is determined to beΓc/Γh=0.187±0.031 (stat)±0.023 (sys). The probability for ab quark to fragment into\(\bar B_s \) orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a\(\bar B^0 \) orB−.
Using full data sample.
Using full data sample with proper time > 1 ps to enrich (b bbar) content.
Data with Delta(L) > 1.
A determination of the hadronic fragmentation functions of the Z 0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 ⩽ Q 2 ⩽ 8312 GeV 2 and x (= P h E beam ) > 0.08 . A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: α s ( M Z ) = 0.118 ± 0.005. The corresponding QCD scale for five quark flavours is: Λ (5) MS = 230 ± 60 MeV .
No description provided.
Extraction of strong coupling constant ALP_S and the LAMQCD)MSBAR values.
We have measured the B0B¯0 mixing probability, χd, using a sample of 965 000 BB¯ pairs from Υ(4S) decays. Counting dilepton events, we find χd=0.157±0.016±0.018−0.021+0.028. Using tagged B0 events, we find χd=0.149±0.023±0.019±0.010. The first (second) error is statistical (systematic). The third error reflects a ±15% uncertainty in the assumption, made in both cases, that charged and neutral B pairs contribute equally to dilepton events. We also obtain a limit on the CP impurity in the Bd0 system, ‖Re(εB0)‖<0.045 at 90% C.L.
No description provided.
Mixing parameter from counting dilepton events. CONST(N=MIXING PARAM) = 1/(1 - LAMBDA(C,N)) * (N(2LEPTON+) + N(2LEPTON-))/(N(LEPTON+,LEPTON-) + N(2LEPTON+) + N(2LEPTON-)). LAMBDA(C,N) is the fraction of dilepton events coming from B+B- decays, LAMBDA(C,N) = f(B+)*Br(B+)**2/(f(B+)*Br(B+)**2 + f(B0)*Br(B0)**2), where f(B+),f(B0) are the productiron fractions of the charged and neutral B's at the UPSI(4S), and Br(B+), Br(B0) are the semileptonic brancing fractions.
Mixing parameter from tagged B0 events.
The strong coupling constant, αs, has been determined in hadronic decays of theZ0 resonance, using measurements of seven observables relating to global event shapes, energy correlatio
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
Data corrected for finite acceptance and resolution of the detector and for intial state photon radiation. No corrections for hadronic effects are applied.. Errors include statistical and systematic uncertainties, added in quadrature.
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 from 1990 running period.
Data from 1990 running period.
Data from 1990 running period.
A new measurement of αs is obtained from the distributions in thrust, heavy jet mass, energy-energy correlation and two recently introduced jet broadening variables following a method proposed by Cata
Thrust distribution corrected for detector acceptance and initial state photon radiation.
Heavy jet mass (RHO) distribution (THRUST definition) corrected for detect or acceptance and initial state photon radiation.
Heavy jet mass (RHOM) distribution (MASS definition) corrected for detectoracceptance and initial state photon radiation.
The production dynamics of baryon-antibaryon pairs are investigated using hadronic Z 0 decays, recorded with the OPAL detector, which contain at least two identified Λ baryons. The rapidly difference for Λ Λ pairs shows the correlations expected from models with a chain-like production of baryon-antibaryon pairs. If the baryon number of a Λ is compensated by a Λ , the Λ is found with a probability of 53% in an interval of ±0.6 around the Λ rapidity. This correlation strength is weaker than predicted by the Herwig Monte Carlo and the Jetset Monte Carlo with a production chain of baryon-antibaryon, and stronger than predicted by the UCLA model. The observed rapidity correlations can be described by the Jetset Monte Carlo with a dominant production chain of baryon-meson-antibaryon, the popcorn mechanism. In addition to the short range correlations, one finds an indication of a correlation of Λ Λ pairs in opposite hemispheres if both the Λ and the Λ have large rapidities. Such long range correlations are expected if the primary quark flavours are compensated in opposite hemispheres and if these quarks are found in energetic baryons. Rates for simultaneous baryon and strangeness number compensation for Λ Λ , Ξ − Ξ + and Ξ − Λ ( Λ + Λ ) are measured and compared with different Monte Carlo models.
No description provided.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified LAMBDA(LAMBDABAR). CT.= Data read from plot.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified XI-(XIBAR+). CT.= Data read from plot.
Forum