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1.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,14(4):613-631
A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap
regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass
energies; in particular at the Z pole
taking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard
Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was
determined:
The parity violating coupling of the s quark to the Z was determined to be:
Received: 8 October 1999 / Revised version: 23 February 2000 / Published online: 18 May 2000 相似文献
2.
The longitudinal polarization, the transverse polarization, and the forward-backward asymmetry of baryons, have been measured using a sample of 4.34 million hadronic decays collected with the OPAL detector at LEP between 1990 and 1995. These results are important as an aid to the understanding
of hadronization mechanisms. Significant longitudinal polarization has been observed at intermediate and high momentum. For
( 0.3, the longitudinal polarization has been measured to be (stat) 5.2 (syst)%. We have observed no transverse polarization. A significant forward-backward asymmetry has been measured and
can be described by a JETSET model.
Received: 30 July 1997 相似文献
3.
《Zeitschrift fur Physik C Particles and Fields》1997,76(3):387-400
Using approximately 4.3 million hadronic Z0 decays collected with the OPAL detector at LEP between 1990 and 1995, we measure the branching fractions of the Z0 into up-type and down-type light quarks, Rq, and the forwardbackward asymmetries, AFB(q), using high-momentum stable particles as a tag. Adopting a method that employs double tagged events to determine the flavour tagging efficiencies, and assuming the flavour independence of strong interactions and SU(2) isospin symmetry, we measure: 相似文献
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G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》1999,11(2):239-250
A multidimensional study of local multiplicity fluctuations and multiparticle correlations of hadrons produced in Z decays is performed. The study is based on the data sample of more than events recorded with the OPAL detector at LEP. The fluctuations and correlations are analysed in terms of the normalized
scaled factorial moments and cumulants up to the fifth order. The moments are observed to have intermittency-like behaviour,
which is found to be more pronounced with increasing dimension. The large data sample allows for the first time a study of
the factorial cumulants in annihilation. The analysis of the cumulants shows the existence of genuine multiparticle correlations with a strong intermittency
rise up to higher orders. These correlations are found to be stronger in higher dimensions. The decomposition of the factorial
moments into lower-order correlations shows that the dynamical fluctuations have important contributions from genuine many-particle
correlations. The Monte Carlo models Jetset 7.4 and Herwig 5.9 are found to reproduce the trend of the measured moments and cumulants but they underestimate the magnitudes. The results
are found to be consistent with QCD jet formation dynamics, although additional contributions from other mechanisms cannot
be excluded.
Received: 8 February 1999 / Published online: 8 September 1999 相似文献
6.
Abe K Abe K Abe T Adam I Akimoto H Aston D Baird KG Baltay C Band HR Barklow TL Bauer JM Bellodi G Berger R Blaylock G Bogart JR Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Calcaterra A Cassell R Chou A Cohn HO Coller JA Convery MR Cook V Cowan RF Crawford G Damerell CJ Daoudi M de Groot N de Sangro R Dong DN Doser M Dubois R Erofeeva I Eschenburg V Etzion E Fahey S Falciai D Fernandez JP Flood K Frey R Hart EL Hasuko K Hertzbach SS Huffer ME Huynh X Iwasaki M 《Physical review letters》2001,86(7):1162-1166
We present final measurements of the Z boson-lepton coupling asymmetry parameters A(e), A(mu), and A(tau) with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure A(e) = 0.1544+/-0.0060, A(mu) = 0.142+/-0.015, and A(tau) = 0.136+/-0.015. Combined with our left-right asymmetry measured from hadronic decays, we find A(e) = 0.1516+/-0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin (2)theta(eff)(W) = 0.230 98+/-0.000 26. 相似文献
7.
D. Abbaneo P. Antilogus T. Behnke S.C. Blyth M. Elsing R. Faccini R.W.L. Jones K. Mönig S. Petzold R. Tenchini 《The European Physical Journal C - Particles and Fields》1998,4(2):185-191
Measurements of the forward-backward production asymmetry of heavy quarks in Z decays provide a precise determination of
. The asymmetries are sensitive to QCD effects, in particular hard gluon radiation. In this paper QCD corrections for and are discussed. The interplay between the experimental techniques used to measure the asymmetries and the QCD effects is
investigated using simulated events. A procedure to estimate the correction needed for experimental measurements is proposed,
and some specific examples are given.
Received: 26 February 1998 / Published online: 2 June 1998 相似文献
8.
The inclusive production rates and differential cross-sections of photons and mesons with a final state containing photons
have been measured with the OPAL detector at LEP. The light mesons covered by the measurements are the , , , , and a. The particle multiplicities per hadronic Zdecay, extrapolated to the full energy range, are: where the first errors are statistical and the second systematic. In general, the results are in agreement with the predictions
of the JETSET and HERWIG Monte Carlo models.
Received: 9 April 1998 / Published online: 12 August 1998 相似文献
9.
The results of a comprehensive series of measurements of the cross-sections for the photo-production of π0-mesons from hydrogen at pion c.m. angles from 47 to 145 degrees are presented. The minimum and maximum photon energies have been 238 and 922 MeV respectively. 相似文献
10.
We discuss the Bose–Einstein interference effect in multi-particle production. After a short review of various methods of
implementation of this effect into Monte Carlo generators the weight method is presented in more detail and used to analyze
the data for hadronic decays. In particular, we consider the possibility of deducing the two-particle weight factor from the experimental data.
Received: 23 September 1999 / Published online: 3 February 2000 相似文献
11.
Abstract. We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with
the L3 detector in the years 1993–95. A total luminosity of was collected at centre-of-mass energies and which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved
determination of Z parameters. From the total cross sections, combined with our measurements in 1990–92, we obtain the final
results:
An invisible width of is derived which in the Standard Model yields for the number of light neutrino species . Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector
coupling constants of the neutral weak current to charged leptons are determined to be and . Including our measurements of the forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our
measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of GeV is set at 95% confidence level.
Received: 4 February 2000 / Published online: 18 May 2000 相似文献
12.
The measurement of the forward-backward asymmetries of heavy quarks provides one of the most precise determinations of sin2
W
inZ decays. We discuss in detail the one-loop QCD radiative corrections to these asymmetries. Results are given for single heavy-quark jet asymmetries and asymmetries of the thrust axis, as well as for heavy-quark two-jet final states. 相似文献
13.
The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged
particles produced in collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse and longitudinal components of the total hadronic cross section are evaluated from the measured fragmentation functions. They are found to be and respectively. The strong coupling constant is calculated from in next-to-leading order of perturbative QCD, giving Including non-perturbative power corrections leads to The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity,
The fragmentation functions and multiplicities in and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow
the gluon fragmentation function to be evaluated.
Received: 12 September 1997 / Published online: 19 October 1998 相似文献
14.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2000,16(3):423-433
Bose-Einstein correlations in pairs of identical charged pions produced in a sample of 4.3 million Z hadronic decays are studied as a function of the three components of the momentum difference, transverse (“out” and “side”)
and longitudinal with respect to the thrust direction of the event. A significant difference between the transverse, r, and longitudinal, r, dimensions is observed, indicating that the emitting source of identical pions, as observed in the Longitudinally CoMoving
System, has an elongated shape. This is observed with a variety of selection techniques. Specifically, the values of the parameters
obtained by fitting the extended Goldhaber parametrisation to the correlation function ${\mathrm C'} ={\mathrm C^{DATA}}/{\mathrm
C^{MC}}$ for two-jet events, selected with the Durham algorithm and resolution parameter y = 0.04, are r = (0.809 0.009 (stat) (syst)) fm, r = (0.989 0.011 (stat) ({\it syst})) fm and r/r = 1.222 0.027 (stat) (syst). The results are discussed in the context of a recent model of Bose-Einstein correlations based on string fragmentation.
The results of a unidimensional analysis are also presented.
Received: 3 January 2000 / Published online: 8 June 2000 相似文献
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Using the OPAL detector at LEP, the running of the effective QED coupling α(t) is measured for space-like momentum transfer from the angular distribution of small-angle Bhabha scattering. In an almost
ideal QED framework, with very favourable experimental conditions, we obtain:
where the first error is statistical, the second is the experimental systematic and the third is the theoretical uncertainty.
This agrees with current evaluations of α(t). The null hypothesis that α remains constant within the above interval of -t is excluded with a significance above 5σ. Similarly, our results are inconsistent at the level of 3σ with the hypothesis
that only leptonic loops contribute to the running. This is currently the most significant direct measurement where the running
α(t) is probed differentially within the measured t range.
Received: 2 March 2005, Revised: 30 August 2005, Published online: 3 November 2005 相似文献
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