8,911 research outputs found
Computing for Perturbative QCD - A Snowmass White Paper
We present a study on high-performance computing and large-scale distributed
computing for perturbative QCD calculations.Comment: 21 pages, 5 table
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
Computational Particle Physics for Event Generators and Data Analysis
High-energy physics data analysis relies heavily on the comparison between
experimental and simulated data as stressed lately by the Higgs search at LHC
and the recent identification of a Higgs-like new boson. The first link in the
full simulation chain is the event generation both for background and for
expected signals. Nowadays event generators are based on the automatic
computation of matrix element or amplitude for each process of interest.
Moreover, recent analysis techniques based on the matrix element likelihood
method assign probabilities for every event to belong to any of a given set of
possible processes. This method originally used for the top mass measurement,
although computing intensive, has shown its power at LHC to extract the new
boson signal from the background.
Serving both needs, the automatic calculation of matrix element is therefore
more than ever of prime importance for particle physics. Initiated in the
eighties, the techniques have matured for the lowest order calculations
(tree-level), but become complex and CPU time consuming when higher order
calculations involving loop diagrams are necessary like for QCD processes at
LHC. New calculation techniques for next-to-leading order (NLO) have surfaced
making possible the generation of processes with many final state particles (up
to 6). If NLO calculations are in many cases under control, although not yet
fully automatic, even higher precision calculations involving processes at
2-loops or more remain a big challenge.
After a short introduction to particle physics and to the related theoretical
framework, we will review some of the computing techniques that have been
developed to make these calculations automatic. The main available packages and
some of the most important applications for simulation and data analysis, in
particular at LHC will also be summarized.Comment: 19 pages, 11 figures, Proceedings of CCP (Conference on Computational
Physics) Oct. 2012, Osaka (Japan) in IOP Journal of Physics: Conference
Serie
GoSam: A program for automated one-loop Calculations
The program package GoSam is presented which aims at the automated
calculation of one-loop amplitudes for multi-particle processes. The amplitudes
are generated in terms of Feynman diagrams and can be reduced using either
D-dimensional integrand-level decomposition or tensor reduction, or a
combination of both. GoSam can be used to calculate one-loop corrections to
both QCD and electroweak theory, and model files for theories Beyond the
Standard Model can be linked as well. A standard interface to programs
calculating real radiation is also included. The flexibility of the program is
demonstrated by various examples.Comment: 10 pages, Talk given at the International Workshop on Advanced
Computing and Analysis Techniques in Physics Research (ACAT), Uxbridge,
London, September 201
Automation of NLO QCD and EW corrections with Sherpa and Recola
This publication presents the combination of the one-loop matrix-element
generator Recola with the multipurpose Monte Carlo program Sherpa. Since both
programs are highly automated, the resulting Sherpa+Recola framework allows for
the computation of -in principle- any Standard Model process at both NLO QCD
and EW accuracy. To illustrate this, three representative LHC processes have
been computed at NLO QCD and EW: vector-boson production in association with
jets, off-shell Z-boson pair production, and the production of a top-quark pair
in association with a Higgs boson. In addition to fixed-order computations,
when considering QCD corrections, all functionalities of Sherpa, i.e. particle
decays, QCD parton showers, hadronisation, underlying events, etc. can be used
in combination with Recola. This is demonstrated by the merging and matching of
one-loop QCD matrix elements for Drell-Yan production in association with jets
to the parton shower. The implementation is fully automatised, thus making it a
perfect tool for both experimentalists and theorists who want to use
state-of-the-art predictions at NLO accuracy.Comment: 38 pages, 29 figures. Matches the published version (few typos
corrected
HW/HZ + 0 and 1 jet at NLO with the POWHEG BOX interfaced to GoSam and their merging within MiNLO
We present a generator for the production of a Higgs boson H in association
with a vector boson V=W or Z (including subsequent V decay) plus zero and one
jet, that can be used in conjunction with general-purpose shower Monte Carlo
generators, according to the POWHEG method, as implemented within the POWHEG
BOX framework. We have computed the virtual corrections using GoSam, a program
for the automatic construction of virtual amplitudes. In order to do so, we
have built a general interface of the POWHEG BOX to the GoSam package. With
this addition, the construction of a POWHEG generator within the POWHEG BOX is
now fully automatized, except for the construction of the Born phase space. Our
HV + 1 jet generators can be run with the recently proposed MiNLO method for
the choice of scales and the inclusion of Sudakov form factors. Since the HV
production is very similar to V production, we were able to apply an improved
MiNLO procedure, that was recently used in H and V production, also in the
present case. This procedure is such that the resulting generator achieves NLO
accuracy not only for inclusive distributions in HV + 1 jet production but also
in HV production, i.e. when the associated jet is not resolved, yielding a
further example of matched calculation with no matching scale.Comment: 22 pages, 18 figures. Version accepted for publication on JHE
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
Modern Feynman Diagrammatic One-Loop Calculations
In this talk we present techniques for calculating one-loop amplitudes for
multi-leg processes using Feynman diagrammatic methods in a semi-algebraic
context. Our approach combines the advantages of the different methods allowing
for a fast evaluation of the amplitude while monitoring the numerical stability
of the calculation. In phase space regions close to singular kinematics we use
a method avoiding spurious Gram determinants in the calculation. As an
application of our approach we report on the status of the calculation of the
amplitude for the process .Comment: 10 pages, 2 figures; contribution to the proceedings of the CPP2010
Workshop, 23-25 Sep. 2010, KEK, Tsukuba, Japa
NLO merging in tt+jets
In this talk the application of the recently introduced methods to merge NLO
calculations of successive jet multiplicities to the production of top pairs in
association with jets will be discussed, in particular a fresh look is taken at
the top quark forward-backward asymmetries. Emphasis will be put on the
achieved theoretical accuracy and the associated perturbative and
non-perturbative error estimates.Comment: 6 pages, 3 figures, proceedings contribution for EPS 2013, Stockholm,
17-24 Jul
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