A
bstract
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
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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.
We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different ...implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.
A standard file format is proposed to store process and event information, primarily output from parton-level event generators for further use by general-purpose ones. The information content is ...identical with what was already defined by the Les Houches Accord five years ago, but then in terms of Fortran commonblocks. This information is embedded in a minimal XML-style structure, for clarity and to simplify parsing.
Is Vtb≃1? Alwall, J.; Frederix, R.; Gérard, J.-M. ...
The European physical journal. C, Particles and fields,
2/2007, Letnik:
49, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The strongest constraint on Vtb presently comes from the 3×3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If unitarity is relaxed, current information from top production at ...Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker, and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.
New Developments in MadGraph/MadEvent Alwall, J; Artoisenet, P; de Visscher, S ...
AIP conference proceedings,
01/2008, Letnik:
1078, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
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 a package for automatic calculation of Feynman rules and model files from the Lagrangian of any New Physics model.
Low-Q2 photons do not resolve partons in the proton, which gives problems when applying the deep inelastic scattering formalism, such as an unphysical, negative gluon density extracted from data. ...Considering instead hadronic fluctuations of the photon, we show that the generalised vector meson dominance model (GVDM) gives a good description of the measured cross section at low Q2, i.e., reproduces F2(x,Q2), using only few parameters with essentially known values. Combining GVDM and parton density functions makes it possible to obtain a good description of F2 data over the whole range of x and Q2.
In order to simulate the multi-jets events in a reliable way, a matrix-element generator and a parton shower generator have to be used simultaneously. To avoid the problem of overlapping between ...their respective phase-spaces, various jet matching techniques can be used in the context of the Standard Model. Beyond the Standard Model, many models propose the existence of heavy particles for which the QCD radiation should be harder, justifying again the use of such technique. MADGRAPH/MADEVENT allows to apply the matching also beyond in this case. We present here the ongoing work in the context of the production of heavy particles in the MSSM.
Traces historical developments and political reforms from 17th to late 20th centuries, and examines social processes of immigration and secularization and conditions of Jewish and Muslim minority ...groups, Catholics and non-Lutherans, assimilation and integration trends, new religious movements, inequalities, and recent legal decisions made by parliament to separate church and state.
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