152 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
Precise numerical evaluation of the two loop sunrise graph Master Integrals in the equal mass case
We present a double precision routine in Fortran for the precise and fast
numerical evaluation of the two Master Integrals (MIs) of the equal mass
two-loop sunrise graph for arbitrary momentum transfer in d=2 and d=4
dimensions. The routine implements the accelerated power series expansions
obtained by solving the corresponding differential equations for the MIs at
their singular points. With a maximum of 22 terms for the worst case expansion
a relative precision of better than a part in 10^{15} is achieved for arbitrary
real values of the momentum transfer.Comment: 11 pages, LaTeX. The complete paper is also available via the www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints/ and the program can be
downloaded from http://www-ttp.physik.uni-karlsruhe.de/Progdata
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
Logarithmic electroweak corrections to hadronic Z+1 jet production at large transverse momentum
We consider hadronic production of a Z boson in association with a jet and
study one- and two-loop electroweak logarithmic corrections in the region of
high Z-boson transverse momentum, p_T >> M_Z, including leading and
next-to-leading logarithms. Numerical results for the LHC and Tevatron
colliders are presented. At the LHC these corrections amount to tens of per
cent and will be important for interpretation of the measurements.Comment: 10 pages, 4 figures; one reference added; minor improvements.
Accepted for publication in Phys. Lett.
NLO QCD corrections to pp -> t anti-t b anti-b + X at the LHC
We report on the calculation of the full next-to-leading order QCD
corrections to the production of top anti-top bottom anti-bottom (ttbb) final
states at the LHC, which deliver a serious background contribution to the
production of a Higgs boson (decaying into a bottom anti-bottom pair) in
association with a top anti-top 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.Comment: 4 pages, LaTeX, 4 postscript figures. Reference added, minor
modifications. Matches published versio
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
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