88 research outputs found
Off-shell production of top-antitop pairs in the lepton+jets channel at NLO QCD
The production of top-quark pairs that subsequently decay hadronically and
leptonically (lepton+jets channel) is one of the key processes for the study of
top-quark properties at the LHC. In this article, NLO QCD corrections of order
to the hadronic process
are
presented. The computation includes off-shell as well as non-resonant
contributions, and experimental event selections are used in order to provide
realistic predictions. The results are provided in the form of cross sections
and differential distributions. The QCD corrections are sizeable and different
from the ones of the fully leptonic channel. This is due to the different final
state where here four jets are present at leading order.Comment: 24 pages, 24 eps-figures. Matches the published versio
NLO electroweak corrections to off-shell top-antitop production with leptonic decays at the LHC
For the first time the next-to-leading-order electroweak corrections to the
full off-shell production of two top quarks that decay leptonically are
presented. This calculation includes all off-shell, non-resonant, and
interference effects for the 6-particle phase space. While the electroweak
corrections are below one per cent for the integrated cross section, they reach
up to 15% in the high-transverse-momentum region of distributions. To support
the results of the complete one-loop calculation, we have in addition evaluated
the electroweak corrections in two different pole approximations, one requiring
two on-shell top quarks and one featuring two on-shell W bosons. While the
former deviates by up to 10% from the full calculation for certain
distributions, the latter provides a very good description for most
observables. The increased centre-of-mass energy of the LHC makes the inclusion
of electroweak corrections extremely relevant as they are particularly large in
the Sudakov regime where new physics is expected to be probed.Comment: 33 pages,23 eps-figures. Matches the published version. Typo fixed in
equations (2.18) and (2.19
NLO electroweak corrections to vector-boson scattering at the LHC
Recently, a measurement of the vector-boson scattering process with same-sign
W bosons has been reported by the CMS collaboration. Hence it is of prime
importance to have precise predictions with next-to-leading order (NLO)
accuracy. In these proceedings, we report on a recent NLO electroweak
computation to the full process . As realistic experimental event selections are applied to
the final state, it can directly be compared with experimental measurements.
This is particularly important as the corrections turn out to be surprisingly
large and even exceed the NLO QCD corrections. The NLO electroweak predictions
are presented at the cross-section and differential distribution level.Comment: 5 pages, 4 figures. Proceedings to the XXV International Workshop on
Deep-Inelastic Scattering and Related Subjects, 3-7 April 2017, Birmingham,
U
Electroweak corrections to vector-boson scattering
We report on a recent calculation of the complete NLO QCD and electroweak
corrections to the process , i.e. like-sign
charged vector-boson scattering. The computation is based on the complete
amplitudes involving two different orders of the strong and electroweak
coupling constants at tree level and three different orders at one-loop level.
We find electroweak corrections of for the fiducial cross section that
are an intrinsic feature of the vector-boson scattering process. For
differential distributions, the corrections reach up to in the
phase-space regions explored. At the NLO level a unique separation between
vector-boson scattering and irreducible background processes is not possible
any more at the level of Feynman diagrams.Comment: 6 pages, 8 eps figures, Prodeedings of the 13th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), 25-29 September, 2017, St. Gilgen, Austri
Electroweak fragmentation functions for dark matter annihilation
Electroweak corrections can play a crucial role in dark matter annihilation.
The emission of gauge bosons, in particular, leads to a secondary flux
consisting of all Standard Model particles, and may be described by electroweak
fragmentation functions. To assess the quality of the fragmentation function
approximation to electroweak radiation in dark matter annihilation, we have
calculated the flux of secondary particles from gauge-boson emission in models
with Majorana fermion and vector dark matter, respectively. For both models, we
have compared cross sections and energy spectra of positrons and antiprotons
after propagation through the galactic halo in the fragmentation function
approximation and in the full calculation. Fragmentation functions fail to
describe the particle fluxes in the case of Majorana fermion annihilation into
light fermions: the helicity suppression of the lowest-order cross section in
such models cannot be lifted by the leading logarithmic contributions included
in the fragmentation function approach. However, for other classes of models
like vector dark matter, where the lowest-order cross section is not
suppressed, electroweak fragmentation functions provide a simple,
model-independent and accurate description of secondary particle fluxes.Comment: 18 pages, matches the published versio
NLO QCD and EW corrections to processes involving off-shell top quarks
We review recent results on next-to-leading order (NLO) QCD and electroweak
(EW) corrections for processes involving off-shell top quarks. For the
off-shell production of two top quarks that decay leptonically, the full NLO EW
corrections have been computed. For the very same process in association with a
Higgs boson, EW corrections have been calculated and combined with existing NLO
QCD corrections. In both cases, selected differential distributions are shown.
In these proceedings, particular emphasis is put on the effect of the EW
corrections as well as the off-shell contributions.Comment: 6 pages, 6 figures. Contribution to the proceedings of the 13th
International Symposium on Radiative Corrections (RADCOR 2017
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