Measurement Of Αs Research Articles

Measurement of αs and the non-strange spectral functions in hadronic τ decays with OPAL

The spectral functions of the vector current and the axial-vector current have been measured in hadronic τ decays using the OPAL detector at LEP. Within the framework of the Operator Product Expansion a simultaneous determination of the strong coupling constant α s, the non-perturbative operators of dimension 6 and 8 and of the gluon condensate has been performed. Different perturbative descriptions have been compared to the data. The Contour Improved Fixed Order Perturbation Theory gives α s( m τ 2) = 0.348 ± 0.009 exp ± 0.019 theo at the τ-mass scale and α s( m Z 2) = 0.1219 ± 0.0010 exp ± 0.0017 theo at the Z 0-mass scale. The values obtained for α s( m Z 2) using Fixed Order Perturbation Theory of Renormalon Chain Resummation are 2.3% and 4.1% smaller, respectively. The ‘running’ of the strong coupling between s 0 ⋍ 1.3 GeV 2 and s 0 = m τ 2 has been tested from direct fits to the integrated differential hadronic decay rate R τ ( s 0). A test of the saturation of chiral sum rules at the τ-mass scale has been performed.

Measurements of αs with the Delphi detector at Lep

The data collected with Delphi during the Lep1 period is used to perform a simultaneous fit to the strong coupling constant α s in 2 nd order perturbation theory and to the renormalisation scale χ μ . The results are compared to α s fits in 2 nd order perturbation theory with fixed scale χ μ and to other theoretically motivated scale setting methods. To determine the energy dependence of α s , event shape distributions and their mean values are measured for √ s = 48 GeV to 189 GeV. The strong coupling α s is extractd in O ( α s 2), Next to Leading Log Approximation (NLLA) and in a combined scheme using hadronisation corrections-evaluated with fragmentation model generators, and an analytical power ansatz.

Measurement of αs and the non-strange spectral functions in hadronic τ decays with OPAL

The spectral functions of the vector current and the axial-vector current have been measured in hadronic τ decays using the OPAL detector at LEP. Within the framework of the Operator Product Expansion a simultaneous determination of the strong coupling constant α s, the non-perturbative operators of dimension 6 and 8 and of the gluon condensate has been performed. Different perturbative descriptions have been compared to the data. The Contour Improved Fixed Order Perturbation Theory gives α s( m τ 2) = 0.348 ± 0.009 exp ± 0.019 theo at the τ-mass scale and α s( m Z 2) = 0.1219 ± 0.0010 exp ± 0.0017 theo at the Z 0-mass scale. The values obtained for α s( m Z 2) using Fixed Order Perturbation Theory or Renormalon Chain Resummation are 2.3% and 4.1% smaller, respectively. The ‘running’ of the strong coupling between s 0 ≅ 1.3 GeV 2 and s 0 = m τ 2 has been tested from direct fits to the integrated differential hadronic decay rate R τ ( s 0). A test of saturation of QCD sum rules at the τ-mass scale has been performed.

The measurement of αs( Mτ) in ALEPH

The measurement of the τ spectral functions and the extraction of the value α s ( M τ ) in ALEPH detector is described. The present results is α s ( M τ ) = 0.352 ± 0.007 exp ± 0.016 theo , which translates using the renormalization-group equations to α s ( M Z ) = 0.1217 ± 0.0007 exp ± 0.0017 theo ± 0.0010 evol . Combining errors gives α s ( M Z ) = 0.1217 ± 0.0021, which is preliminary in view of the continuing work by theorists and experimentalists.

Annihilation of S-wave quarkonia and the measurement of αs

We analyze the relativistic corrections to annihilation rates of S-wave quarkonia within the framework of NRQCD. We show that order v^2 corrections can be expressed in terms of the heavy quark pole mass and the quarkonium mass. The ratio of hadronic to radiative annihilation rates for eta_b and eta_c can therefore be predicted accurately. The contributions of color-octet operators to the hadronic decay rates of spin-triplet quarkonia are shown to be significant, even though they arise at order v^4 in the velocity expansion. We provide a rough estimate of the color-octet contributions and extract the value of alpha_s from the experimental data on Upsilon decays.

Study of hadronic events and measurements of αs between 30 and 91 GeV

We have studied the structure of hadronic events with a hard, %radiated isolated photon in the final state ($\mathrm{e^{+}e^{-}} \rightarrow$ Z $\rightarrow$ hadrons $+$ $\gamma$) in the 3.6 million hadronic data collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed $\cal{O} \alpha_{s}^{2})$ calculations to determine the strong coupling constant $\alpha_{s}$ over a wide range of energies. We find that the strong coupling constant $\alpha_{s}$ decreases with increasing energy, as expected from QCD.

A measurement of αs from the scaling violation in e+e− annihilation

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z 0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is α s ( M Z ) = 0.124 −0.007 +0.006(exp) ± 0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence.

HERA Workshop on proton, photon and pomeron structure

HERA Workshop on proton, photon and pomeron structure

Measurement of αs from jet rates in deep inelastic scattering at HERA

Jet production in deep inelastic scattering for 120 < Q 2 < 3600 GeV 2 has been studied using data from an integrated luminosity of 3.2 pb −1 collected with the ZEUS detector at HERA. Jets are identified with the JADE algorithm. A cut on the angular distribution of parton emission in the γ ∗- parton centre-of-mass system minimises the experimental and theoretical uncertainties in the determination of the jet rates. The jet rates, when compared to O ( α s 2) perturbative QCD calculations, allow a precise determination of α s ( Q ) in three Q 2-intervals. The values are consistent with a running of ifα s ( Q ), as expected from QCD. Extrapolating to Q = M Z 0 α s ( M Z 0 ) = 0.117 ± 0.005 (stat) −0.005 +0.004 (syst exp) ± 0.007 (syst theory).

Measurement of αs from scaling violations in fragmentation functions in e+e− annihilation

A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented. Data samples enriched in uds, c, b and gluon jets, respectively, together with measurements of the longitudinal and transverse inclusive cross sections are used to extract the fragmentation function for the gluon and for each flavour. The measurements are compared to data from experiments at energies between 22 GeV and 91 GeV and scaling violations consistent with QCD predictions are observed. From this, a measurement of the strong coupling constant α s ( Mz) = 0.126 ±0.009 is obtained.

Measurement of αS from τ decays

We present measurements of spectral moments extracted from the invariant mass distributions of the final states of hadronic τ decay products recorded in the CLEO detector. From a fit of theoretical predictions to the measurements of spectral moments and the total hadronic decay width of the τ, we determine the strong coupling constant and a set of non-perturbative QCD parameters. The strong coupling constant is measured to be α s ( m τ ) = 0.306 ± 0.024, which when extrapolated to the Z mass, yields α s ( M z ) = 0.114 ± 0.003.

Measurements of αs in e+e- annihilation at /TRISTAN

The strong coupling constant α s was determined from analyses of the thrust, heavy jet mass and, differential 2-jet rate, using e + e - hadronic events at s = 58 GeV with the TOPAZ detector at TRISTAN. The NLLjet Monte Carlo simulation (NLLjet) and analytic formulae based on resummation up to the next-to-leading logarithms combined with O( α 2 s ) calculations were used to evaluate α s . The average α s values at Q 2 = (58 GeV) 2 from the analyses are α s = 0.125 ± 0.009 for NLLjet and α s = 0.132 ± 0.008 for the resummed analytic formulae.

Measurement of αs from the moment of particle momenta within jets from e+e- annihilation

We present a study of the third moment of the inclusive momentum distribution of particles within jets produced by e + e - annihilation at TRISTAN. In this analysis, the QCD coupling strength α s is determined by fits to the prediction of the Next-to-Leading Logarithm Parton-Shower model. The measured value of α s (57.9 GeV) = 0.134 -0.005 +0.006.

Determination of? s using the next-to-leading-log approximation of QCD

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 Catani, Trentadue, Turnock and Webber. This method includes the full calculation ofO(s2) terms and leading and next-to-leading logarithms resummed to all orders of αs. The analysis is based on data taken with the DELPHI detector at LEP during 1991. I its found that the inclusion of the resummed leading and next-to-leading logarithms reduces the scale dependence of αs and allows an extension of the fit range towards the infrared limit of the kinematical range. The combined value for αs obtained at the scale μ2=MZ2 is: $$\alpha _s (M_Z^2 ) = 0.123 \pm 0.006.$$

A measurement of αs and of higher twists from a QCD analysis of high statistics F2 data on hydrogen and deuterium targets

We compare the Q 2-dependence of the highest statistics structure function data on free or quasi-free nucleons — from the BCDMS Collaborations and the SLAC experiments — with the predictions of perturbative QCD. An excellent is observed, leading to a precise measurement of the strong interaction coupling contant, α s( M z 2)=0.113±0.005, a measurement of higher-twist terms in the Q 2-evolution of F 2 and an estimate of the gluon distribution in the range 0.07< χ<0.25.

Measurement of αs from the structure of particle clusters produced in hadronic Z decays

Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant α s is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C-parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Y cut , before these variables are computed. The combined result from all shape variables of pre-clustered events is α s( M Z 2 = 0.117±0.005 for a renormalization scale μ= 1 2 M Z . For μ values between M Z and the b-quark mass, the result changes by −0.009 +0.006.

Measurements of αs in e +e − annihilation at √ s=53.3 GeV and 59.5 GeV

We studied the energy-energy correlation (EEC) and its asymmetry (AEEC) using e +e − hadronic annihilation events obtained at √ s=53.3 GeV and 59.5 GeV with the TOPAZ detector at the TRISTAN collider. We used a Monte Carlo simulation combined with the QCD matrix elements by Gottschalk and Shatz and the Lund string fragmentation model. By comparing the experimental data with simulated events, we determined the strong coupling constant α s at both energies. The results are 0.129±0.007 (stat) ±0.010 (syst) at √ s=53.3 GeV and 0.122±0.008 (stat) ±0.010 (syst) at 59.5 GeV.

Evaluation of Portable Optical Property Measurement Equipment for Solar Selective Surfaces

The operation and accuracy of portable optical measurement equipment for determining the solar absorptance, αs, and emittance, ε, of solar selective surfaces are presented. The optical equipment includes a Gier Dunkle Solar Reflectometer (Model MS-251) and a Willey Alpha Meter (Model 2150) for αs measurements and a Gier Dunkle Infrared Reflectometer (Model DB-100) and a Willey Ambient Emissometer (Model 2158) for ε measurements. The accuracy of the MS-251 for measurements of αs for electrodeposited black chrome coatings was determined to be better than ±0.03 absorptance units. For the same coatings, the Willey Alpha Meter accuracy was limited by deviations up to 0.11 absorptance units. The accuracy of the Gier Dunkle Infrared Reflectometer for ε(100°C) measurements is better than ±0.02 emittance units. Values for ε(100°C) determined with the Willey Emissometer using black chrome coatings are higher than the actual 100°C emittance. However, since the relationship is linear, the correct emittance can be calculated by multiplication by a constant factor.