71 research outputs found
MadGraph5_AMC@NLO and top pair production at a Linear Collider
In these proceedings, we will present the latest update on the madgraph5_aMC@NLO via a short tutorial both for production at leading and next-toleading order. Finally, we will present some preliminary study of the top quark pair
production at next-to-leading order
The Matrix Element Method and QCD Radiation
The matrix element method (MEM) has been extensively used for the analysis of
top-quark and W-boson physics at the Tevatron, but in general without dedicated
treatment of initial state QCD radiation. At the LHC, the increased center of
mass energy leads to a significant increase in the amount of QCD radiation,
which makes it mandatory to carefully account for its effects. We here present
several methods for inclusion of QCD radiation effects in the MEM, and apply
them to mass determination in the presence of multiple invisible particles in
the final state. We demonstrate significantly improved results compared to the
standard treatment.Comment: 15 pp; v2: references and some clarifications added; v3: discussion
of NLO effects, version published in PR
Automation of the matrix element reweighting method
Matrix element reweighting is a powerful experimental technique widely
employed to maximize the amount of information that can be extracted from a
collider data set. We present a procedure that allows to automatically evaluate
the weights for any process of interest in the standard model and beyond. Given
the initial, intermediate and final state particles, and the transfer functions
for the final physics objects, such as leptons, jets, missing transverse
energy, our algorithm creates a phase-space mapping designed to efficiently
perform the integration of the squared matrix element and the transfer
functions. The implementation builds up on MadGraph, it is completely
automatized and publicly available. A few sample applications are presented
that show the capabilities of the code and illustrate the possibilities for new
studies that such an approach opens up.Comment: 41 pages, 21 figure
Determination of differential cross sections from t¯t fully leptonic, using the matrix element method
The purpose of this work is the development of a new analysis technique that allows the determination of differential cross sections with respect to arbitrary kinematic variables. This is illustrated for top quark pairs production where two leptons are present in the final state together with two neutrinos that cannot be detected. By estimating the t¯t invariant mass and the angle between
the top quarks in the t¯t rest frame, the sensitivity to the presence of new physics is demonstrated. This technique, based on the matrix element method, makes the
optimal use of the experimental information given a set of theoretical hypotheses
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
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
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
Simulating spin-3/2 particles at colliders
Support for interactions of spin-3/2 particles is implemented in the
FeynRules and ALOHA packages and tested with the MadGraph 5 and CalcHEP event
generators in the context of three phenomenological applications. In the first,
we implement a spin-3/2 Majorana gravitino field, as in local supersymmetric
models, and study gravitino and gluino pair-production. In the second, a
spin-3/2 Dirac top-quark excitation, inspired from compositness models, is
implemented. We then investigate both top-quark excitation and top-quark
pair-production. In the third, a general effective operator for a spin-3/2
Dirac quark excitation is implemented, followed by a calculation of the angular
distribution of the s-channel production mechanism.Comment: 20 pages, 7 figure
Les Houches 2013: Physics at TeV Colliders: Standard Model Working Group Report
This Report summarizes the proceedings of the 2013 Les Houches workshop on
Physics at TeV Colliders. Session 1 dealt primarily with (1) the techniques for
calculating standard model multi-leg NLO and NNLO QCD and NLO EW cross sections
and (2) the comparison of those cross sections with LHC data from Run 1, and
projections for future measurements in Run 2.Comment: Proceedings of the Standard Model Working Group of the 2013 Les
Houches Workshop, Physics at TeV Colliders, Les houches 3-21 June 2013. 200
page
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