4,194 research outputs found
The infrared structure of e+ e- --> 3 jets at NNLO reloaded
This paper gives detailed information on the structure of the infrared
singularities for the process e+ e- --> 3 jets at next-to-next-to-leading order
in perturbation theory. Particular emphasis is put on singularities associated
to soft gluons. The knowledge of the singularity structure allows the
construction of appropriate subtraction terms, which in turn can be implemented
into a numerical Monte Carlo program.Comment: 59 pages, additional comments added, version to be publishe
NNLO QCD corrections to event shape variables in electron positron annihilation
Precision studies of QCD at electron-positron colliders are based on
measurements of event shapes and jet rates. To match the high experimental
accuracy, theoretical predictions to next-to-next-to-leading order (NNLO) in
QCD are needed for a reliable interpretation of the data. We report the first
calculation of NNLO corrections O(alpha_s^3) to three-jet production and
related event shapes, and discuss their phenomenological impact.Comment: Contributed to 2007 Europhysics Conference on High Energy Physics,
Manchester, England 19-25 July 200
Antenna subtraction with massive fermions at NNLO: Double real initial-final configurations
We derive the integrated forms of specific initial-final tree-level
four-parton antenna functions involving a massless initial-state parton and a
massive final-state fermion as hard radiators. These antennae are needed in the
subtraction terms required to evaluate the double real corrections to
hadronic production at the NNLO level stemming from the partonic
processes and .Comment: 24 pages, 1 figure, 1 Mathematica file attache
NNLO corrections to event shapes in annihilation
We compute the next-to-next-to-leading order (NNLO) QCD corrections to the
six most important event shape variables related to three-particle final states
in electron-positron annihilation. The corrections are sizeable for all
variables, however their magnitude is substantially different for different
observables. We observe that the NNLO corrections yield a considerably better
agreement between theory and experimental data both in shape and normalisation
of the event shape distributions. The renormalisation scale dependence of the
theoretical prediction is substantially reduced compared to the previously
existing NLO results. Our results will allow a precise determination of the
strong coupling constant from event shape data collected at LEP.Comment: 30 pages, LaTeX, numercial results corrected for oversubtraction of
large-angle soft radiatio
Hadronization effects in event shape moments
We study the moments of hadronic event shapes in annihilation within
the context of next-to-next-to-leading order (NNLO) perturbative QCD
predictions combined with non-perturbative power corrections in the dispersive
model. This model is extended to match upon the NNLO perturbative prediction.
The resulting theoretical expression has been compared to experimental data
from JADE and OPAL, and a new value for has been determined, as
well as of the average coupling in the non-perturbative region below
GeV within the dispersive model:
\alpha_s(M_Z)&=0.1153\pm0.0017(\mathrm{exp})\pm0.0023(\mathrm{th}),\alpha_0&=0.5132\pm0.0115(\mathrm{exp})\pm0.0381(\mathrm{th}),
The precision of the value has been improved in comparison to
the previously available next-to-leading order analysis. We observe that the
resulting power corrections are considerably larger than those estimated from
hadronization models in multi-purpose event generator programs.Comment: 23 pages, 5 figures, 15 tables. Few minor changes. Version accepted
for publication in European Physical Journal C
Antenna subtraction for gluon scattering at NNLO
We use the antenna subtraction method to isolate the double real radiation
infrared singularities present in gluonic scattering amplitudes at
next-to-next-to-leading order. The antenna subtraction framework has been
successfully applied to the calculation of NNLO corrections to the 3-jet cross
section and related event shape distributions in electron-positron
annihilation. Here we consider processes with two coloured particles in the
initial state, and in particular two-jet production at hadron colliders such as
the Large Hadron Collider (LHC). We construct a subtraction term that describes
the single and double unresolved contributions from the six-gluon tree-level
process using antenna functions with initial state partons and show numerically
that the subtraction term correctly approximates the matrix elements in the
various single and double unresolved configurations.Comment: 71 pages, JHEP3 class; corrected typos, equivalent but more compact
version of eq. (5.12), results unchange
La vie du contrat dans les commandes publiques. Het leven van de overeenkomst in de oveheidsopdrachten. pp. 7-44 (1ère partie) et pp.115-140 (2e partie)
W boson production at hadron colliders: the lepton charge asymmetry in NNLO QCD
We consider the production of W bosons in hadron collisions, and the
subsequent leptonic decay W->lnu_l. We study the asymmetry between the rapidity
distributions of the charged leptons, and we present its computation up to the
next-to-next-to-leading order (NNLO) in QCD perturbation theory. Our
calculation includes the dependence on the lepton kinematical cuts that are
necessarily applied to select W-> lnu_l events in actual experimental analyses
at hadron colliders. We illustrate the main differences between the W and
lepton charge asymmetry, and we discuss their physical origin and the effect of
the QCD radiative corrections. We show detailed numerical results on the charge
asymmetry in ppbar collisions at the Tevatron, and we discuss the comparison
with some of the available data. Some illustrative results on the lepton charge
asymmetry in pp collisions at LHC energies are presented.Comment: 37 pages, 21 figure
Resummation of heavy jet mass and comparison to LEP data
The heavy jet mass distribution in e+e- collisions is computed to
next-to-next-to-next-to leading logarithmic (NNNLL) and next-to-next-to leading
fixed order accuracy (NNLO). The singular terms predicted from the resummed
distribution are confirmed by the fixed order distributions allowing a precise
extraction of the unknown soft function coefficients. A number of quantitative
and qualitative comparisons of heavy jet mass and the related thrust
distribution are made. From fitting to ALEPH data, a value of alpha_s is
extracted, alpha_s(m_Z)=0.1220 +/- 0.0031, which is larger than, but not in
conflict with, the corresponding value for thrust. A weighted average of the
two produces alpha_s(m_Z) = 0.1193 +/- 0.0027, consistent with the world
average. A study of the non-perturbative corrections shows that the flat
direction observed for thrust between alpha_s and a simple non-perturbative
shape parameter is not lifted in combining with heavy jet mass. The Monte Carlo
treatment of hadronization gives qualitatively different results for thrust and
heavy jet mass, and we conclude that it cannot be trusted to add power
corrections to the event shape distributions at this accuracy. Whether a more
sophisticated effective field theory approach to power corrections can
reconcile the thrust and heavy jet mass distributions remains an open question.Comment: 33 pages, 14 figures. v2 added effect of lower numerical cutoff with
improved extraction of the soft function constants; power correction
discussion clarified. v3 small typos correcte
Determining ethnic-, gender-, and age-specific waist circumference cut-off points to predict metabolic syndrome: the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) study
Objective: The aim was to determine receiver-operating characteristic (ROC) waist circumference (WC) cut-off points best associated with metabolic syndrome (MetS) in a cohort of South African teachers.Design: Target population study.Setting and subjects: Four hundred and nine urban black (Africans) and white (Caucasians) from the Kenneth Kaunda district in North West province, between the ages of 25 and 65 years old, were stratified according to gender and age (25-45 years and 46-65 years).Outcome measures: Anthropometric, fasting overnight urine and biological markers for MetS.Results: ROC analysis determined pathological WC cut-off points of 91 cm for African men and 84 cm for African women. It is recommended that WC cut-off points should be 97 cm for Caucasian men and 84 cm for Caucasian women. Pathological WC cut-off points significantly predicted MetS in all ethnic-, gender- and age- specific groups, especially in male groups, with odds ratios of 7.6 [95% confidence interval (CI): 3.4-17.1, p-value = 0.00) for African men and 6 (95% CI: 3-12.1, p-value = 0.00) for Caucasian men.Conclusion: ROC-developed WC cut-off points were found to be good predictors of MetS in a South African cohort, especially in the men. Further research in prospective cohort studies is warranted to verify our findings.Keywords: SABPA study, waist circumference cut-off points, metabolic syndrome, Met
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