87 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
QCD and electroweak corrections to WZ scattering at the LHC
We present the first computation of the full next-to-leading-order QCD and
electroweak corrections to the WZ scattering process at the LHC. All off-shell,
gauge-boson-decay, and interference effects are taken into account for the
process at the orders and . The electroweak
corrections feature the typical Sudakov behaviour towards high energy and
amount to relative to the electroweak contribution to the integrated
cross section. Moreover, the corrections induce significant shape distortions
in differential distributions. The next-to-leading-order analysis of the quark-
and gluon-induced channels is supplemented by a leading-order study of all
possible contributions to the full 4\ell+2\mbox{jets} production cross
section in a realistic fiducial phase-space volume
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
The second physical moment of the heavy quark vector correlator at O(alpha_s^3)
The second moment of the heavy quark vector correlator at O(alpha_s^3) is
presented. The implications of this result on recent determinations of the
charm and bottom quark mass are discussed.Comment: 9 pages, physics discussion extende
Low energy moments of heavy quark current correlators at four loops
We describe several techniques for the calculation of multi-loop integrals
and their application to heavy quark current correlators. As new results, we
present the four-loop correction to the second and third physical moment in the
low-energy expansions of vector, axial-vector and scalar quark current
correlators. Using a Ward identity, we obtain the third and fourth moment for
the pseudo-scalar correlator. We briefly discuss the impact of these results on
the determination of the charm quark mass and the strong coupling constant
using lattice simulations for the current correlators and of the charm- and
bottom-quark mass from experimental data for \sigma(e^+ e^- -> hadrons).Comment: 21 page
Automatic one-loop calculations with Sherpa+OpenLoops
We report on the OpenLoops generator for one-loop matrix elements and its application to four-lepton production in association with up to one jet. The open loops algorithm uses a numerical recursion to construct the numerator of one-loop Feynman diagrams as functions of the loop momentum. In combination with tensor integrals this results in a highly efficient and numerically stable matrix element generator. In order to obtain a fully automated setup for the simulation of next-to-leading order scattering processes we interfaced OpenLoops to the Sherpa Monte Carlo event generator
Reconstruction of heavy quark current correlators at O(\alpha_s^3)
We construct approximate formulas for the O(\alpha_s^3) QCD contributions to
vector, axial-vector, scalar and pseudo-scalar quark current correlators, which
are valid for arbitrary values of momenta and masses. The derivation is based
on conformal mapping and the Pade approximation procedure and incorporates
known expansions in the low energy, threshold and high energy regions. We use
our results to estimate additional terms in these expansions.Comment: 24 pages, 4 figure
Higher Moments of Heavy Quark Correlators in the Low Energy Limit at O(alpha_s^2)
We present the first 30 moments of the low energy expansions of the vector,
axial-vector, scalar and pseudo-scalar heavy quark correlation functions at
three-loop order, including the singlet contribution which appears for the
first time at three loops. In addition we compare the behavior of the moments
for large n with the prediction from threshold calculations.Comment: 32 pages, 7 figure
Precise Charm- and Bottom-Quark Masses: Theoretical and Experimental Uncertainties
Recent theoretical and experimental improvements in the determination of
charm and bottom quark masses are discussed. A new and improved evaluation of
the contribution from the gluon condensate to the
charm mass determination and a detailed study of potential uncertainties in the
continuum cross section for production is presented, together with a
study of the parametric uncertainty from the -dependence of our
results. The final results, MeV and
MeV, represent, together with a closely related lattice
determination MeV, the presently most precise
determinations of these two fundamental Standard Model parameters. A critical
analysis of the theoretical and experimental uncertainties is presented.Comment: 12 pages, presented at Quarks~2010, 16th International Seminar of
High Energy Physics, Kolomna, Russia, June 6-12, 2010; v2: references adde
Standard and epsilon-finite Master Integrals for the rho-Parameter
We have constructed an epsilon-finite basis of master integrals for all new
types of one-scale tadpoles which appear in the calculation of the four-loop
QCD corrections to the electroweak rho-parameter. Using transformation rules
from the epsilon-finite basis to the standard minimal-number-of-lines basis, we
obtain as a by-product analytical expressions for few leading terms of the
epsilon-expansion of all members of the standard basis. The new master
integrals have been computed with the help of the Pade method and by use of
difference equations independently.Comment: 26 page
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