619 research outputs found
Drell-Yan, ZZ, W+W- production in SM & ADD model to NLO+PS accuracy at the LHC
In this paper, we present the next-to-leading order QCD corrections for
di-lepton, di-electroweak boson (ZZ, W+W-) production in both the SM and the
ADD model, matched to the HERWIG parton-shower using the aMC@NLO framework. A
selection of results at the 8 TeV LHC, which exhibits deviation from the SM as
a result of the large extra-dimension scenario are presented.Comment: 12 pages, 10 figures, search sensitivity for the 14 TeV LHC
discussed, version to appear in Eur. Phys. J.
Higgs production in association with bottom quarks
We study the production of a Higgs boson in association with bottom quarks in
hadronic collisions, and present phenomenological predictions relevant to the
13 TeV LHC. Our results are accurate to the next-to-leading order in QCD, and
matched to parton showers through the MC@NLO method; thus, they are fully
differential and based on unweighted events, which we shower by using both
Herwig++ and Pythia8. We perform the computation in both the four-flavour and
the five-flavour schemes, whose results we compare extensively at the level of
exclusive observables. In the case of the Higgs transverse momentum, we also
consider the analytically-resummed cross section up to the NNLO+NNLL accuracy.
In addition, we analyse at the effects of the
interference between the and gluon-fusion production modes.Comment: 33 pages, 17 figure
Four-lepton production at hadron colliders: aMC@NLO predictions with theoretical uncertainties
We use aMC@NLO to study the production of four charged leptons at the LHC,
performing parton showers with both HERWIG and Pythia6. Our underlying matrix
element calculation features the full next-to-leading order
result and the contribution of the channel, and it
includes all off-shell, spin-correlation, virtual-photon-exchange, and
interference effects. We present several key distributions together with the
corresponding theoretical uncertainties. These are obtained through a
process-independent technique that allows aMC@NLO to compute scale and PDF
uncertainties in a fully automated way and at no extra CPU-time costComment: 24 pages, 6 figure
Higgs pair production at the LHC with NLO and parton-shower effects
We present predictions for the SM-Higgs-pair production channels of relevance
at the LHC: gluon-gluon fusion, VBF, and top-pair, W, Z and single-top
associated production. All these results are at the NLO accuracy in QCD, and
matched to parton showers by means of the MC@NLO method; hence, they are fully
differential. With the exception of the gluon-gluon fusion process, for which a
special treatment is needed in order to improve upon the infinite-top-mass
limit, our predictions are obtained in a fully automatic way within the
publicly available MadGraph5_aMC@NLO framework. We show that for all channels
in general, and for gluon-gluon fusion and top-pair associated production in
particular, NLO corrections reduce the theoretical uncertainties, and are
needed in order to arrive at reliable predictions for total rates as well as
for distributions.Comment: 11 pages, 7 figures, version accepted for publication on PL
On the reduction of negative weights in MC@NLO-type matching procedures
We show how a careful analysis of the behaviour of a parton shower Monte
Carlo in the vicinity of the soft and collinear regions allows one to formulate
a modified MC@NLO-matching prescription that reduces the number of
negative-weight events with respect to that stemming from the standard MC@NLO
procedure. As a first practical application of such a prescription, that we dub
MC@NLO-, we have implemented it in the MadGraph5_aMC@NLO framework, by
employing the Pythia8 Monte Carlo. We present selected MC@NLO- results
at the 13 TeV LHC, and compare them with MC@NLO ones. We find that the former
predictions are consistent with the latter ones within the typical matching
systematics, and that the reduction of negative-weight events is significant.Comment: 44 pages, 13 figures; several minor text amendments and one figure
adde
Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
We present results for the QCD next-to-leading order (NLO) calculation of
single-top t-channel production in the 4-flavour scheme, interfaced to Parton
Shower (PS) Monte Carlo programs according to the POWHEG and MC@NLO methods.
Comparisons between the two methods, as well as with the corresponding process
in the 5-flavour scheme are presented. For the first time results for typical
kinematic distributions of the spectator-b jet are presented in an NLO+PS
approach.Comment: 16+1 pages, 8 figures, matches version accepted for publication in
JHE
New Developments in MadGraph/MadEvent
We here present some recent developments of MadGraph/MadEvent since the
latest published version, 4.0. These developments include: Jet matching with
Pythia parton showers for both Standard Model and Beyond the Standard Model
processes, decay chain functionality, decay width calculation and decay
simulation, process generation for the Grid, a package for calculation of
quarkonium amplitudes, calculation of Matrix Element weights for experimental
events, automatic dipole subtraction for next-to-leading order calculations,
and an interface to FeynRules, a package for automatic calculation of Feynman
rules and model files from the Lagrangian of any New Physics model.Comment: 6 pages, 3 figures. Plenary talk given at SUSY08, Seoul, South Korea,
June 2008. To appear in the proceeding
The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
We discuss the theoretical bases that underpin the automation of the
computations of tree-level and next-to-leading order cross sections, of their
matching to parton shower simulations, and of the merging of matched samples
that differ by light-parton multiplicities. We present a computer program,
MadGraph5_aMC@NLO, capable of handling all these computations -- parton-level
fixed order, shower-matched, merged -- in a unified framework whose defining
features are flexibility, high level of parallelisation, and human intervention
limited to input physics quantities. We demonstrate the potential of the
program by presenting selected phenomenological applications relevant to the
LHC and to a 1-TeV collider. While next-to-leading order results are
restricted to QCD corrections to SM processes in the first public version, we
show that from the user viewpoint no changes have to be expected in the case of
corrections due to any given renormalisable Lagrangian, and that the
implementation of these are well under way.Comment: 158 pages, 27 figures; a few references have been adde
Scalar and pseudoscalar Higgs production in association with a top-antitop pair
We present the calculation of scalar and pseudoscalar Higgs production in
association with a top-antitop pair to the next-to-leading order (NLO) accuracy
in QCD, interfaced with parton showers according to the MC@NLO formalism. We
apply our results to the cases of light and very light Higgs boson production
at the LHC, giving results for total rates as well as for sample differential
distributions, relevant to the Higgs, to the top quarks, and to their decay
products. This work constitutes the first phenomenological application of
aMC@NLO, a fully automated approach to complete event generation at NLO in QCD.Comment: 15 pages, 8 figures, published version. (2 references added, improved
description of the decay of the top and Higgs bosons
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