We report on the calculation of the full next-to-leading-order QCD corrections to the production of ttbb final states at the LHC, which deliver a serious background contribution to the production of ...a Higgs boson (decaying into a bb pair) in association with a tt pair. While the corrections significantly reduce the unphysical scale dependence of the leading-order cross section, our results predict an enhancement of the ttbb production cross section by a K factor of about 1.8.
We present predictions for
production at the LHC in next-to-leading order QCD. The precise description of this background process is a prerequisite to observe associated
production in the
decay ...channel and to directly measure the top-quark Yukawa coupling at the LHC. The leading-order cross section is extremely sensitive to scale variations. We observe that the traditional scale choice adopted in ATLAS simulations underestimates the
background by a factor two and introduce a new dynamical scale that stabilizes the perturbative predictions. We study various kinematic distributions and observe that the corrections have little impact on their shapes if standard cuts are applied. In the regime of highly boosted Higgs bosons, which offers better perspectives to observe the
signal, we find significant distortions of the kinematic distributions. The one-loop amplitudes are computed using process-independent algebraic manipulations of Feynman diagrams and numerical tensor reduction. We find that this approach provides very high numerical stability and CPU efficiency.
Extending earlier work, we provide predictions obtained with the Monte Carlo generator
PROPHECY4f for the decays H → ZZ/WW → 4
l including the complete electroweak
O
(
α
)
corrections and some ...higher-order improvements. The gauge-boson resonances are described in the complex-mass scheme. Here, particular attention is paid to a comparison of different final states with identical charges, such as
e
+
e
−
μ
+
μ
−
and
μ
+
μ
−
μ
+
μ
−
.
The \({{\mathcal{O}}}(\alpha)\) electroweak radiative corrections to \({\gamma\gamma\to WW\to 4f}\) within the electroweak standard model are calculated in double-pole approximation (DPA). Virtual ...corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for \({\gamma\gamma\to 4f}{ + }\gamma\). Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called Coffer \(\gamma\gamma\) - the computer code can be obtained from the authors upon request - which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises \({{\mathcal{O}}}(\alpha)\) corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear safety in the observables.
PDF
