205 research outputs found
A unified NLO description of top-pair and associated Wt production
We present an NLO simulation of WWbb production with massive b-quarks at the
LHC. Off-shell and non-resonant contributions associated with top-pair and
single-top channels and with leptonic W-boson decays are consistently taken
into account using the complex-mass scheme. Thanks to the finite b-quark mass,
WWbb predictions can be extended to the whole b-quark phase space, thereby
including Wt-channel single-top contributions that originate from collinear
g->bb splittings in the four-flavour scheme. This provides a consistent NLO
description of tt and Wt production and decay, including quantum interference
effects. The simulation is also applicable to exclusive 0- and 1-jet bins,
which is of great importance for Higgs-boson studies in the H->WW channel and
for any other analysis with large top backgrounds and jet vetoes or jet bins.Comment: 8pp. Minor revision, results unchange
NLO QCD corrections to WWbb production at hadron colliders
Top-antitop quark pairs belong to the most abundantly produced and precisely
measurable heavy-particle signatures at hadron colliders and allow for crucial
tests of the Standard Model and new-physics searches. Here we report on the
calculation of the next-to-leading order (NLO) QCD corrections to hadronic WWbb
production, which provides a complete NLO description of the production of
top-antitop pairs and their subsequent decay into W bosons and bottom quarks,
including interferences, off-shell effects, and non-resonant backgrounds.
Numerical predictions for the Tevatron and the LHC are presented.Comment: 4 pages, 3 figures. Note and reference added; matches version
published in Phys. Rev. Let
NLO QCD+EW predictions for 22v diboson signatures at the LHC
We present next-to-leading order (NLO) calculations including QCD and electroweak (EW) corrections for 22ν diboson signatures with two opposite-charge leptons and two neutrinos. Specifically, we study the processes and , including all relevant off-shell diboson channels, , as well as non-resonant contributions. Photon-induced processes are computed at NLO EW, and we discuss subtle differences related to the definition and the renormalisation of the coupling α for processes with initial- and final-state photons. All calculations are performed within the automated Munich/Sherpa+OpenLoops frameworks, and we provide numerical predictions for the LHC at 13 TeV. The behaviour of the corrections is investigated with emphasis on the high-energy regime, where NLO EW effects can amount to tens of percent due to large Sudakov logarithms. The interplay between and contributions to the same-flavour channel, , is discussed in detail, and a quantitative analysis of photon-induced contributions is presented. Finally, we consider approximations that account for all sources of large logarithms, at high and low energy, by combining virtual EW corrections with a YFS soft-photon resummation or a QED parton shower
production at hadron colliders in NNLO QCD
We consider the production of pairs at hadron colliders. We report
on the first complete and fully differential computation of radiative
corrections at next-to-next-to-leading order in QCD perturbation theory. We
present selected numerical results for pp collisions at 7 TeV and compare them
to available LHC data. We find that the impact of the NNLO QCD corrections on
the fiducial cross section ranges between 4 and 15%, depending on the applied
cuts.Comment: Minor changes, version published on PL
production at hadron colliders in NNLO QCD
Charged gauge boson pair production at the Large Hadron Collider allows
detailed probes of the fundamental structure of electroweak interactions. We
present precise theoretical predictions for on-shell production that
include, for the first time, QCD effects up to next-to-next-to-leading order in
perturbation theory. As compared to next-to-leading order, the inclusive
cross section is enhanced by 9% at 7 TeV and 12% at 14 TeV. The
residual perturbative uncertainty is at the 3% level. The severe contamination
of the cross section due to top-quark resonances is discussed in
detail. Comparing different definitions of top-free production in the
four and five flavour number schemes, we demonstrate that top-quark resonances
can be separated from the inclusive cross section without significant
loss of theoretical precision.Comment: 7 pages, 3 figure
NNLO QCD + NLO EW with Matrix+OpenLoops: precise predictions for vector-boson pair production
We present the first combination of NNLO QCD and NLO EW corrections for vector-boson pair production at the LHC. We consider all final states with two, three and four charged leptons, including resonant and non-resonant diagrams, spin correlations and off-shell effects. Detailed predictions are discussed for three representative channels corresponding to W+W−, W±Z and Z Z production. Both QCD and EW corrections are very significant, and the details of their combination can play a crucial role to achieve the level of precision demanded by experimental analyses. In this context we point out nontrivial issues that arise at large transverse momenta, where the EW corrections are strongly enhanced by Sudakov logarithms and the QCD corrections can feature so-called giant K -factors. Our calculations have been carried out in the Matrix+OpenLoops framework and can be extended to the production of an arbitrary colour singlet in hadronic collisions, provided that the required two-loop QCD amplitudes are available. Combined NNLO QCD and NLO EW predictions for the full set of massive diboson processes will be made publicly available in the next release of Matrix and will be instrumental in advancing precision diboson studies and new-physics searches at the LHC and future hadron colliders
NLO QCD corrections to WZ+jet production with leptonic decays
We compute the next-to-leading order QCD corrections to WZ+jet production at
the Tevatron and the LHC, including decays of the electroweak bosons to light
leptons with all off-shell effects taken into account. The corrections are
sizable and have significant impact on the differential distributions.Comment: 14 pages, 7 figure
Electroweak corrections to Higgs-strahlung off W/Z bosons at the Tevatron and the LHC with HAWK
The associate production of Higgs bosons with W or Z bosons, known as
Higgs-strahlung, is an important search channel for Higgs bosons at the hadron
colliders Tevatron and LHC for low Higgs-boson masses. We refine a previous
calculation of next-to-leading-order electroweak corrections (and recalculate
the QCD corrections) upon including the leptonic decay of the W/Z bosons,
thereby keeping the fully differential information of the 2-lepton + Higgs
final state. The gauge invariance of the W/Z-resonance treatment is ensured by
the use of the complex-mass scheme. The electroweak corrections, which are at
the level of -(5-10)% for total cross sections, further increase in size with
increasing transverse momenta p_T in differential cross sections. For instance,
for p_T,H >~ 200GeV, which is the interesting range at the LHC, the electroweak
corrections to WH production reach about -14% for M_H = 120GeV. The described
corrections are implemented in the HAWK Monte Carlo program, which was
initially designed for the vector-boson-fusion channel, and are discussed for
various distributions in the production channels pp / p \bar p -> H + l nu_l /
l^-l^+ / nu_l \bar nu_l + X.Comment: 22 p
NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders
We present details of a calculation of the cross section for hadronic
top-antitop production in next-to-leading order (NLO) QCD, including the decays
of the top and antitop into bottom quarks and leptons. This calculation is
based on matrix elements for \nu e e+ \mu- \bar{\nu}_{\mu}b\bar{b} production
and includes all non-resonant diagrams, interferences, and off-shell effects of
the top quarks. Such contributions are formally suppressed by the top-quark
width and turn out to be small in the inclusive cross section. However, they
can be strongly enhanced in exclusive observables that play an important role
in Higgs and new-physics searches. Also non-resonant and off-shell effects due
to the finite W-boson width are investigated in detail, but their impact is
much smaller than naively expected. We also introduce a matching approach to
improve NLO calculations involving intermediate unstable particles. Using a
fixed QCD scale leads to perturbative instabilities in the high-energy tails of
distributions, but an appropriate dynamical scale stabilises NLO predictions.
Numerical results for the total cross section, several distributions, and
asymmetries are presented for Tevatron and the LHC at 7 TeV, 8 TeV, and 14 TeV.Comment: 61 pp. Matches version published in JHEP; one more reference adde
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