2,168 research outputs found
Automation of electroweak corrections for LHC processes
For the Run 2 of the LHC next-to-leading order electroweak corrections will
play an important role. Even though they are typically moderate at the level of
total cross sections they can lead to substantial deviations in the shapes of
distributions. In particular for new physics searches but also for a precise
determination of Standard Model observables their inclusion in the theoretical
predictions is mandatory for a reliable estimation of the Standard Model
contribution. In this article we review the status and recent developments in
electroweak calculations and their automation for LHC processes. We discuss
general issues and properties of NLO electroweak corrections and present some
examples, including the full calculation of the NLO corrections to the
production of a W boson in association with two jets computed using GoSaM
interfaced to MadDipole.Comment: LaTex, 60 pages, 8 Figure
Integrated dipoles with MadDipole in the MadGraph framework
Heading towards a full automation of next-to-leading order (NLO) QCD
corrections, one important ingredient is the analytical integration over the
one-particle phase space of the unresolved particle that is necessary when
adding the subtraction terms to the virtual corrections. We present the
implementation of these integrated dipoles in the MadGraph framework. The
result is a package that allows an automated calculation for the NLO real
emission parts of an arbitrary process.Comment: 22 pages, 1 figure. Published version: few reference updates and a
couple of minor corrections to the tex
A Forward Branching Phase-Space Generator
We develop a forward branching phase-space generator for use in
next-to-leading order parton level event generators. By performing 2 -> 3
branchings from a fixed jet phase-space point, all bremsstrahlung events
contributing to the given jet configuration are generated. The resulting
phase-space integration is three-dimensional irrespective of the considered jet
multiplicity. In this first study, we use the forward branching phase-space
generator to calculate in the leading-color approximation next-to-leading order
corrections to fully differential gluonic jet configurations.Comment: 35 pages, 5 figures, 1 tabl
The SM and NLO multileg working group: Summary report
This report summarizes the activities of the SM and NLO Multileg Working
Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26
June, 2009.Comment: 169 pages, Report of the SM and NLO Multileg Working Group for the
Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 200
Scattering AMplitudes from Unitarity-based Reduction Algorithm at the Integrand-level
SAMURAI is a tool for the automated numerical evaluation of one-loop
corrections to any scattering amplitudes within the dimensional-regularization
scheme. It is based on the decomposition of the integrand according to the
OPP-approach, extended to accommodate an implementation of the generalized
d-dimensional unitarity-cuts technique, and uses a polynomial interpolation
exploiting the Discrete Fourier Transform. SAMURAI can process integrands
written either as numerator of Feynman diagrams or as product of tree-level
amplitudes. We discuss some applications, among which the 6- and 8-photon
scattering in QED, and the 6-quark scattering in QCD. SAMURAI has been
implemented as a Fortran90 library, publicly available, and it could be a
useful module for the systematic evaluation of the virtual corrections oriented
towards automating next-to-leading order calculations relevant for the LHC
phenomenology.Comment: 35 pages, 7 figure
Virtual QCD corrections to Higgs boson plus four parton processes
We report on the calculation of virtual processes contributing to the
production of a Higgs boson and two jets in hadron-hadron collisions. The
coupling of the Higgs boson to gluons, via a virtual loop of top quarks, is
treated using an effective theory, valid in the large top quark mass limit. The
calculation is performed by evaluating one-loop diagrams in the effective
theory. The primary method of calculation is a numerical evaluation of the
virtual amplitudes as a Laurent series in , where is the
dimensionality of space-time. For the cases and we confirm the numerical results by an explicit analytic
calculation.Comment: 21 pages, 2 figures. v2 modifies the text to agree with published
version and corrects typos in the analytical expressions for the four quark
amplitude
NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders
We present details of a calculation of the cross section for hadronic
top-antitop production in next-to-leading order (NLO) QCD, including the decays
of the top and antitop into bottom quarks and leptons. This calculation is
based on matrix elements for \nu e e+ \mu- \bar{\nu}_{\mu}b\bar{b} production
and includes all non-resonant diagrams, interferences, and off-shell effects of
the top quarks. Such contributions are formally suppressed by the top-quark
width and turn out to be small in the inclusive cross section. However, they
can be strongly enhanced in exclusive observables that play an important role
in Higgs and new-physics searches. Also non-resonant and off-shell effects due
to the finite W-boson width are investigated in detail, but their impact is
much smaller than naively expected. We also introduce a matching approach to
improve NLO calculations involving intermediate unstable particles. Using a
fixed QCD scale leads to perturbative instabilities in the high-energy tails of
distributions, but an appropriate dynamical scale stabilises NLO predictions.
Numerical results for the total cross section, several distributions, and
asymmetries are presented for Tevatron and the LHC at 7 TeV, 8 TeV, and 14 TeV.Comment: 61 pp. Matches version published in JHEP; one more reference adde
GoSam-2.0: a tool for automated one-loop calculations within the Standard Model and beyond
We present the version 2.0 of the program package GoSam for the automated
calculation of one-loop amplitudes. GoSam is devised to compute one-loop QCD
and/or electroweak corrections to multi-particle processes within and beyond
the Standard Model. The new code contains improvements in the generation and in
the reduction of the amplitudes, performs better in computing time and
numerical accuracy, and has an extended range of applicability. The extended
version of the "Binoth-Les-Houches-Accord" interface to Monte Carlo programs is
also implemented. We give a detailed description of installation and usage of
the code, and illustrate the new features in dedicated examples.Comment: replaced by published version and reference adde
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