539 research outputs found
Diphoton production in association with two bottom jets
We study the production of a photon pair in association with two bottom jets
at the LHC. This process constitutes an important background to double Higgs
production with the subsequent decay of the two Higgs bosons into a pair of
photons and b-quarks respectively. We calculate this process at next-to-leading
order accuracy in QCD and find that QCD corrections lead to a substantial
increase of the production cross section due to new channels opening up at
next-to-leading order and their inclusion is therefore inevitable for a
reliable prediction. Furthermore, the approximation of massless b-quarks is
scrutinized by calculating the process with both massless and massive b-quarks.
We find that the massive bottom quark leads to a substantial reduction of the
cross section where the biggest effect is however due to the use of a four
flavor PDF set and the corresponding smaller values for the strong coupling
constant.Comment: 19 pages, 10 figure
Automation of the Dipole Subtraction Method in MadGraph/MadEvent
We present the implementation of the dipole subtraction formalism for the
real radiation contributions to any next-to-leading order QCD process in the
MadGraph/MadEvent framework. Both massless and massive dipoles are considered.
Starting from a specific (n+1)-particle process the package provides a Fortran
code for all possible dipoles to all Born processes that constitute the
subtraction term to the (n+1)-particle process. The output files are given in
the usual "MadGraph StandAlone" style using helicity amplitudes.Comment: 14 pages, 4 figure
Interference contributions to gluon initiated heavy Higgs production in the Two-Higgs-Doublet Model
We discuss the production of a heavy neutral Higgs boson of a CP-conserving
Two-Higgs-Doublet Model in gluon fusion and its decay into a four-fermion final
state, .
We investigate the interference contributions to invariant mass distributions
of the four-fermion final state and other relevant kinematical observables. The
relative importance of the different contributions is quantified for the
process in the on-shell approximation, . We show that
interferences of the heavy Higgs with the light Higgs boson and background
contributions are essential for a correct description of the differential cross
section. Even though they contribute below to those heavy
Higgs signal cross sections, to which the experiments at the Large Hadron
Collider were sensitive in its first run, we find that they are sizeable in
certain regions of the parameter space that are relevant for future heavy Higgs
boson searches. In fact, the interference contributions can significantly
enhance the experimental sensitivity to the heavy Higgs boson.Comment: 24 pages, 13 figures; minor clarifications, updated references,
matches published versio
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
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
GoSam 2.0: Automated one loop calculations within and beyond the Standard Model
We present GoSam 2.0, a fully automated framework for the generation and
evaluation of one loop amplitudes in multi leg processes. The new version
offers numerous improvements both on generational aspects as well as on the
reduction side. This leads to a faster and more stable code for calculations
within and beyond the Standard Model. Furthermore it contains the extended
version of the standardized interface to Monte Carlo programs which allows for
an easy combination with other existing tools. We briefly describe the
conceptual innovations and present some phenomenological results.Comment: 7 pages, 3 figures, Contribution to the Proceeedings of the 37th
International Conference on High Energy Physics (ICHEP) 2014, Valencia, Spai
Constraints on Electroweak Effective Operators at One Loop
We derive bounds on nine dimension-six operators involving electroweak gauge
bosons and the Higgs boson from precision electroweak data. Four of these
operators contribute at tree level, and five contribute only at one loop. Using
the full power of effective field theory, we show that the bounds on the five
loop-level operators are much weaker than previously claimed, and thus much
weaker than bounds from tree-level processes at high-energy colliders.Comment: 15 page
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