8,406 research outputs found
Higgs characterisation at NLO in QCD: CP properties of the top-quark Yukawa interaction
At the LHC the CP properties of the top-quark Yukawa interaction can be
probed through Higgs production in gluon fusion or in association with top
quarks. We consider the possibility for both CP-even and CP-odd couplings to
the top quark to be present, and study CP-sensitive observables at
next-to-leading order (NLO) in QCD, including parton-shower effects. We show
that the inclusion of NLO corrections sizeably reduces the theoretical
uncertainties, and confirm that di-jet correlations in jet production
through gluon fusion and correlations of the top-quark decay products in production can provide sensitive probes of the CP nature of the Higgs
interactions.Comment: 18 pages, 9 figures, 12 tables; v2: references added, version to
appear in EPJ
Higgs and Z boson associated production via gluon fusion in the SM and the 2HDM
We analyse the associated production of Higgs and boson via heavy-quark
loops at the LHC in the Standard Model and beyond. We first review the main
features of the Born production, and in particular discuss the
high-energy behaviour, angular distributions and boson polarisation. We
then consider the effects of extra QCD radiation as described by the
loop matrix elements, and find that they dominate at high Higgs transverse
momentum. We show how merged samples of 0-- and 1--jet multiplicities, matched
to a parton shower can provide a reliable description of differential
distributions in production. In addition to the Standard Model study,
results in a generic two-Higgs-doublet-model are obtained and presented for a
set of representative and experimentally viable benchmarks for ,
and production. We observe that various interesting features appear
either due to the resonant enhancement of the cross-section or to interference
patterns between resonant and non-resonant contributions.Comment: 29 pages, 12 figure
The Higgs transverse momentum distribution in gluon fusion as a multiscale problem
We consider Higgs production in gluon fusion and in particular the prediction
of the Higgs transverse momentum distribution. We discuss the ambiguities
affecting the matching procedure between fixed order matrix elements and the
resummation to all orders of the terms enhanced by factors.
Following a recent proposal (Grazzini et al., hep-ph/1306.4581), we argue that
the gluon fusion process, computed considering two active quark flavors, is a
multiscale problem from the point of view of the resummation of the collinear
singular terms. We perform an analysis at parton level of the collinear
behavior of the real emission amplitudes; relying on
the collinear singularities structure of the latter, we derive an upper limit
to the range of transverse momenta where the collinear approximation is valid.
This scale is then used as the value of the resummation scale in the analytic
resummation framework or as the value of the parameter in the POWHEG-BOX
code. A variation of this scale can be used to generate an uncertainty band
associated to the matching procedure. Finally, we provide a phenomenological
analysis in the Standard Model, in the Two Higgs Doublet Model and in the
Minimal Supersymmetric Standard Model. In the two latter cases, we provide an
ansatz for the central value of the matching parameters not only for a Standard
Model-like Higgs boson, but also for heavy scalars and in scenarios where the
bottom quark may play the dominant role.Comment: 33 pages, 13 figures; v2 matches version published in JHE
Slepton pair production in the POWHEG BOX
We present an implementation for slepton pair production at hadron colliders
in the POWHEG BOX, a framework for combining next-to-leading order QCD
calculations with parton-shower Monte-Carlo programs. Our code provides a SUSY
Les Houches Accord interface for setting the supersymmetric input parameters.
Decays of the sleptons and parton-shower effects are simulated with PYTHIA.
Focussing on a representative point in the supersymmetric parameter space we
show results for kinematic distributions that can be observed experimentally.
While next-to-leading order QCD corrections are sizable for all distributions,
the parton shower affects the color-neutral particles only marginally.
Pronounced parton-shower effects are found for jet distributions.Comment: 10 pages, 4 figure
Top quark pair production in association with a jet with NLO parton showering
We compute the production cross section of a top-antitop pair in association
with a jet at hadron colliders at next-to-leading order accuracy matched with
parton shower algorithms to make predictions at the hadron level. The parton
shower allows for including the decay of the top quarks at the leading order
accuracy. We use a framework based on three well established numerical codes,
the POWHEG-BOX, used for the calculation of the cross section, HELAC, which
generates the matrix elements for the Born-level, real emission and the virtual
part, and finally a parton shower program, such as PYTHIA or HERWIG, which
generate the parton-shower and hadronization.Comment: changed title, bug in HERWIG analysis corrected, published version
with restructured discussion, but main conclusions unchange
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
THE TOOLS AND MONTE CARLO WORKING GROUP Summary Report from the Les Houches 2009 Workshop on TeV Colliders
This is the summary and introduction to the proceedings contributions for the
Les Houches 2009 "Tools and Monte Carlo" working group.Comment: 144 Pages. Workshop site
http://wwwlapp.in2p3.fr/conferences/LesHouches/Houches2009/ . Conveners were
Butterworth, Maltoni, Moortgat, Richardson, Schumann and Skand
Single-top Wt-channel production matched with parton showers using the POWHEG method
We present results for the next-to-leading order calculation of single-top
Wt-channel production interfaced to Shower Monte Carlo programs, implemented
according to the POWHEG method. A comparison with MC@NLO is carried out.
Results obtained using the PYTHIA shower are also shown and the effect of
typical cuts is briefly discussed.Comment: 23 pages, 9 figure
Higgs boson production in association with top quarks in the POWHEG BOX
We present results from the analytic calculation of top+antitop+Higgs
hadronic production at Next-to-Leading Order in QCD interfaced with
parton-shower Monte Carlo event generators in the POWHEG BOX framework. We
consider kinematic distributions of the top quark and Higgs boson at the 8 TeV
Large Hadron Collider and study the theoretical uncertainties due to specific
choices of renormalization/factorization scales and parton-showering
algorithms, namely PYTHIA and HERWIG. The importance of spin-correlations in
the production and decay stages of a top/antitop quark is discussed on the
example of kinematic distributions of leptons originating from the top/antitop
decays. The corresponding code is now part of the public release of the POWHEG
BOX.Comment: 15 pp, 14 figure
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