93 research outputs found
Planar Two-Loop Five-Parton Amplitudes from Numerical Unitarity
We compute a complete set of independent leading-color two-loop five-parton
amplitudes in QCD. These constitute a fundamental ingredient for the
next-to-next-to-leading order QCD corrections to three-jet production at hadron
colliders. We show how to consistently consider helicity amplitudes with
external fermions in dimensional regularization, allowing the application of a
numerical variant of the unitarity approach. Amplitudes are computed by
exploiting a decomposition of the integrand into master and surface terms that
is independent of the parton type. Master integral coefficients are numerically
computed in either finite-field or floating-point arithmetic and combined with
known analytic master integrals. We recompute two-loop leading-color
four-parton amplitudes as a check of our implementation. Results are presented
for all independent four- and five-parton processes including contributions
with massless closed fermion loops.Comment: v3: corrected wrong signs for five-gluon amplitudes with
vanishing tree
W- and Z-boson production with a massive bottom-quark pair at the Large Hadron Collider
We present total and differential cross sections for W b anti-b and Z b
anti-b production at the CERN Large Hadron Collider with a center-of-mass
energy of 14 TeV, including Next-to-Leading Order (NLO) QCD corrections and
full bottom-quark mass effects. We also provide numerical results obtained with
a center-of-mass energy of 10 TeV. We study the scale uncertainty of the total
cross sections due to the residual renormalization- and factorization-scale
dependence of the truncated perturbative series. While in the case of Z b
anti-b production the scale uncertainty of the total cross section is reduced
by NLO QCD corrections, the W b anti-b production process at NLO in QCD still
suffers from large scale uncertainties, in particular in the inclusive case. We
also perform a detailed comparison with a calculation that considers massless
bottom quarks, as implemented in the Monte Carlo program MCFM. The effects of a
non-zero bottom-quark mass (m_b) cannot be neglected in phase-space regions
where the relevant kinematic observable, such as the transverse momentum of the
bottom quarks or the invariant mass of the bottom-quark pair, are of the order
of m_b. The effects on the total production cross sections are usually smaller
than the residual scale uncertainty at NLO in QCD.Comment: 24 pages, 24 postscript figures, added one reference, a few typos
corrected, version published in PR
Associated Production of a W Boson and One b Jet
We calculate the production of a W boson and a single b jet to
next-to-leading order in QCD at the Fermilab Tevatron and the CERN Large Hadron
Collider. Both exclusive and inclusive cross sections are presented. We
separately consider the cross section for jets containing a single b quark and
jets containing a b-anti b pair. There are a wide variety of processes that
contribute, and it is necessary to include them all in order to have a complete
description at both colliders.Comment: LaTeX, 16 pages, 22 postscript figures; version published in Phys.
Rev.
Leading-Color Two-Loop QCD Corrections for Three-Jet Production at Hadron Colliders
We present the complete set of leading-color two-loop contributions required
to obtain next-to-next-to-leading-order (NNLO) QCD corrections to three-jet
production at hadron colliders. We obtain analytic expressions for a generating
set of finite remainders, valid in the physical region for three-jet
production. The analytic continuation of the known Euclidean-region results is
determined from a small set of numerical evaluations of the amplitudes. We
obtain analytic expressions that are suitable for phenomenological applications
and we present a C++ library for their efficient and stable numerical
evaluation.Comment: Analytic results in ancillary files; link for numerical code in
references. v3: matches the published versio
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