The value of the strong coupling constant,$$\alpha _s (M_{Z^0 } )$$, is determined from a study of 15 d
Differential jet mass distribution for the heavier jet using method T. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
Differential jet mass distribution for the jet mass difference using methodT. The data are corrected for the finite acceptance and resolution of the detec tor and for initial state photon radiation.
Differential jet mass distribution for the heavier jet using method M. The data are corrected for the finite acceptance and resolution of the detector and for initial state photon radiation.
Distributions of event shape variables obtained from 120600 hadronicZ decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant αs are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, αs(MZ), is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model.
Experimental differential Thrust distributions.
Experimental differential Oblateness distributions.
Experimental differential C-parameter distributions.
We report on an improved measurement of the value of the strong coupling constant σ s at the Z 0 peak, using the asymmetry of the energy-energy correlation function. The analysis, based on second-order perturbation theory and a data sample of about 145000 multihadronic Z 0 decays, yields α s ( M z 0 = 0.118±0.001(stat.)±0.003(exp.syst.) −0.004 +0.0009 (theor. syst.), where the theoretical systematic error accounts for uncertainties due to hadronization, the choice of the renormalization scale and unknown higher-order terms. We adjust the parameters of a second-order matrix element Monte Carlo followed by string hadronization to best describe the energy correlation and other hadronic Z 0 decay data. The α s result obtained from this second-order Monte Carlo is found to be unreliable if values of the renormalization scale smaller than about 0.15 E cm are used in the generator.
Value of LAMBDA(MSBAR) and ALPHA_S.. The first systematic error is experimental, the second is from theory.
The EEC and its asymmetry at the hadron level, unfolded for initial-state radiation and for detector acceptance and resolution. Errors include full statistical and systematic uncertainties.
The properties of final state photons in multihadronic decays of theZ0 and those of the recoiling hadronic system are discussed and compared with theoretical expectations. The yield of two and three jet events with final state photons is found to be in good agreement with the expectation from a matrix element calculation ofO(ααs. Uncertainties in the interpretation of the theoretical calculation do not yet permit a final assessment of events with just one reconstructed jet. Comparing the rates of two jet events with a photon to those of three jet events in the inclusive multihadronic sample, the strong coupling constant in second order is determined asαs\((M_{Z^0 } )\)=0.122±0.010, taking into account only the statistical and experimental systematic errors. It is found that an abelian model of the strong interaction does not describe the data. The comparison of the total yield and the jet rates with QCD shower programs shows better agreement with the ARIADNE model than with the JETSET model. Both programs are found to describe well the photon properties and the properties of the residual hadronic event.
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The error includes the experimental uncertainties (±0.003), uncertainties of hadronisation corrections and of the degree of parton virtualities to which the data are corrected, as well as the uncertainty of choosing the renormalisation scale.
Jet production rates using the E0 recombination scheme.
Jet production rates using the E recombination scheme.
Jet production rates using the p0 recombination scheme.
We have studied the energy-energy angular correlations in hadronic final states from Z 0 decay using the DELPHI detector at LEP. From a comparison with Monte Carlo calculations based on the exact second order QCD matrix element and string fragmentation we find that Λ (5) MS =104 +25 -20 ( stat. ) +25 -20( syst. ) +30 00 ) theor. ) . MeV, which corresponds to α s (91 GeV)=0.106±0.003(stat.)±0.003(syst.) +0.003 -0.000 (theor). The theoretical error stems from different choices for the renormalization scale of α s . In the Monte Carlo simulation the scale of α s as well as the fragmentation parameters have been optimized to described reasonably well all aspects of multihadron production.
Data requested from the authors.
Values of LAMBDA-MSBAR(5) and ALPHA-S(91 GeV) deduced from the EEC measurements. The second systematic error is from the theory.
From an analysis of multi-hadron events from Z 0 decays, values of the strong coupling constant α s ( M 2 Z 0 )=0.131±0.006 (exp)±0.002(theor.) and α s ( M z 0 2 ) = −0.009 +0.007 (exp.) −0.002 +0.006 (theor.) are derived from the energy-energy correlation distribution and its asymmetry, respectively, assuming the QCD renormalization scale μ = M Z 0 . The theoretical error accounts for differences between O ( α 2 s ) calculations. A two parameter fit Λ MS and the renormalization scale μ leads to Λ MS =216±85 MeV and μ 2 s =0.027±0.013 or to α s ( M 2 Z 0 )=0.117 +0.006 −0.008 (exp.) for the energy-energy correlation distribution. The energy-energy correlation asymmetry distribution is insensitive to a scale change: thus the α s value quoted above for this variable includes the theoretical uncertainty associated with the renormalization scale.
Data are at the hadron level, unfolded for initial-state radiation and for detector acceptance and resolution. Note that the systematic errors between bins are correlated.
Alpha-s determined from the EEC measurements. The systematic error is an error in the theory.
Alpha-s determined from the AEEC measurements. The systematic error is an error in the theory.
The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e + e − storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(α 2 s ) QCD matrix element calculations and the QCD scale parameter Λ MS is determined for different parametrizations of the renormalization scale ω 2 . Including all uncertainties our result is α s ( M 2 Z )=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.].
Corrected jet rates.
Second systematic error is theoretical.
We have measured the total normalized cross section R for the process e + e − → hadrons at centre-of-mass energies between 14.0 and 46.8 GeV based on an integrated luminosity of 60.3 pb −1 . The data are well described by the standard SU(3) c ⊗SU(2) L ⊗U(1) model with the production of the five known quarks. No open production of a sixth quark with charge 2/3 or 1/3 occurs below a centre-of-mass energy of 46.6 or 46.3 GeV, respectively. A fitting procedure which takes the correlations between measurements into account was used to determine the electroweak mixing angle sin 2 θ w and the strong coupling constant α s ( S ) in second-order QCD. We applied this procedure to the CELLO data and in addition included the data from other experiments at PETRA and PEP. Both fits give consistent results. The fit to the combined data yields α s (34 2 GeV 2 ) = 0.165±0.030, and sin 2 θ w = 0.236±0.020. Fixing sin 2 θ w at the world average value of 0.23 yields α s (34 2 GeV 2 ) = 0.169±0.025.
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Hadronic events obtained with the CELLO detector at PETRA are compared with second order QCD predictions using different models for the fragmentation of quarks and gluons into hadrons. We find that the model dependence in the determination of the strong coupling constant persists when going from first to second order QCD calculations.
ASYMMETRY FOR DATA CORRECTED WITH IF MODEL (ALPHA-S=0.12).
ASSYMETRY FOR DATA CORRECTED WITH SF MODEL (ALPHA-S=0.19).
No description provided.
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