222 research outputs found
Non-perturbative contribution to the thrust distribution in e(+)e(-) annihilation
We re-evaluate the non-perturbative contribution to the thrust distribution
in hadrons, in the light of the latest experimental data and the
recent NNLO perturbative calculation of this quantity. By extending the
calculation to NNLO+NLL accuracy, we perform the most detailed study to date of
the effects of non-perturbative physics on this observable. In particular, we
investigate how well a model based on a low-scale QCD effective coupling can
account for such effects. We find that the difference between the improved
perturbative distribution and the experimental data is consistent with a
-dependent non-perturbative shift in the distribution, as predicted by the
effective coupling model. Best fit values of and are obtained with
. This is consistent with NLO+NLL results but the quality
of fit is improved. The agreement in is non-trivial because a part
of the 1/Q-dependent contribution (the infrared renormalon) is included in the
NNLO perturbative correction
Recommended from our members
The MC@NLO 3.2 Event Generator
This is the user's manual of MC@NLO 3.2. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, lepton pairs, and Higgs bosons in association with a W
or Z. Spin correlations in decays are included for all processes except ttbar,
single-t, ZZ, and WZ production. This document is self-contained, but we
emphasise the main differences with respect to previous versions
The MC@NLO 3.3 Event Generator
This is the user's manual of MC@NLO 3.3. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, lepton pairs, and Higgs bosons in association with a W
or Z. Spin correlations are included for all processes except ZZ and WZ
production. This document is self-contained, but we emphasise the main
differences with respect to previous versions
Recommended from our members
The MC@NLO 3.2 Event Generator
This is the user's manual of MC@NLO 3.2. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, lepton pairs, and Higgs bosons in association with a W
or Z. Spin correlations in decays are included for all processes except ttbar,
single-t, ZZ, and WZ production. This document is self-contained, but we
emphasise the main differences with respect to previous versions
The MC@NLO 3.3 Event Generator
This is the user's manual of MC@NLO 3.3. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, lepton pairs, and Higgs bosons in association with a W
or Z. Spin correlations are included for all processes except ZZ and WZ
production. This document is self-contained, but we emphasise the main
differences with respect to previous versions
Jet fragmentation in e^+e^- annihilation
A short review of theoretical and experimental results on fragmentation in
e^+e^- annihilation is presented. Starting with an introduction of the concept
of fragmentation functions in e^+e^- annihilation, aspects of scaling
violation, multiplicities, small and large x, longitudinal, gluon, light and
heavy quark fragmentation are summarized
Matching NLO QCD and parton showers in heavy flavour production
We apply the MC@NLO approach to the process of heavy flavour hadroproduction.
MC@NLO is a method for matching next-to-leading order (NLO) QCD calculations
and parton shower Monte Carlo (MC) simulations, with the following features:
fully exclusive events are generated, with hadronisation according to the MC
model; total rates are accurate to NLO; NLO results for distributions are
recovered upon expansion in \as; hard emissions are treated as in NLO
computations while soft/collinear emissions are handled by the MC simulation,
with the same logarithmic accuracy as the MC; matching between the hard and
soft regions is smooth, and no intermediate integration steps are necessary.
The method was applied previously to the hadroproduction of gauge boson pairs,
which at NLO involves only initial-state QCD radiation and a unique colour
structure. In heavy flavour production, it is necessary to include
contributions from final-state QCD radiation and different colour flows. We
present illustrative results on top and bottom production at the Tevatron and
LHC
Measuring sparticle masses in non-universal string inspired models at the LHC
We demonstrate that some of the suggested five supergravity points for study
at the LHC could be approximately derived from perturbative string theories or
M-theory, but that charge and colour breaking minima would result. As a pilot
study, we then analyse a perturbative string model with non-universal soft
masses that are optimised in order to avoid global charge and colour breaking
minima. By combining measurements of up to six kinematic edges from squark
decay chains with data from a new kinematic variable, designed to improve
slepton mass measurements, we demonstrate that a typical LHC experiment will be
able to determine squark, slepton and neutralino masses with an accuracy
sufficient to permit an optimised model to be distinguished from a similar
standard SUGRA point. The technique thus generalizes SUSY searches at the LHC
Angular correlations of lepton pairs from vector boson and top quark decays in Monte Carlo simulations
We explain how angular correlations in leptonic decays of vector bosons and
top quarks can be included in Monte Carlo parton showers, in particular those
matched to NLO QCD computations. We consider the production of pairs of
leptons, originating from the decays of electroweak vector bosons or of
top quarks, in the narrow-width approximation. In the latter case, the
information on the quarks emerging from the decays is also retained. We
give results of implementing this procedure in MC@NL
Single-top production in MC@NLO
We match next-to-leading order QCD results for single-top hadroproduction
with parton shower Monte Carlo simulations, according to the prescription of
the MC@NLO formalism. In this way, we achieve the first practical
implementation in MC@NLO of a process that has both initial- and final-state
collinear singularities. We show that no difficulties of principle arise from
this complication, and present selected results relevant to the Tevatron
- …