61 research outputs found
Production-decay interferences at NLO in QCD for t-channel single-top production
We present a calculation of O(\alpha_s) contributions to the process of
t-channel single-top production and decay, which include virtual and real
corrections arising from interference of the production and decay subprocesses.
The calculation is organized as a simultaneous expansion of the matrix elements
in the couplings \alpha_{ew},\alpha_s and the virtuality of the intermediate
top quark, (p_t^2-m_t^2)/m_t^2 ~ \Gamma_t/m_t, and extends earlier results
beyond the narrow-width approximation.Comment: 33 pages, 6 Figure
Soft and Coulomb gluon resummation in squark-antisquark production at the LHC
We present results for a combined resummation of soft and Coloumb gluon
corrections in squark-antisquark production at the LHC, including the
non-trivial interference of the two effects and the contribution of
squark-antisquark bound states below threshold. The total correction to the
next-to-leading order approximation is found to be sizeable, and amounts to
5-14 % in the squark mass region 200 GeV-2 TeV. The scale dependence of the
total cross section is also reduced.Comment: 6 pages, 3 figures, to appear in the proceedings of the 9th
International Symposium on Radiative Corrections (RADCOR 2009), October 25-30
2009, Ascona, Switzerlan
Four-fermion production near the W-pair production threshold
I report on recent results for the total production cross section of the
process e- e+ -> mu- nubar_mu u dbar X near the W-pair production threshold up
to next-to-leading order in GammaW/MW alpha v^2 obtained in the framework of
unstable-particle effective field theory. Remaining theoretical uncertainties
and their impact on the experimental determination of the W mass are discussed.Comment: To appear in the proceedings of the 8th International Symposium on
Radiative Corrections, October 1-5, 2007, Florence, Ital
Threshold expansion of massive coloured particle cross sections
Pair production of massive coloured particles in hadron collisions is
accompanied by potentially large radiative corrections related to the
suppression of soft gluon emission and enhanced Coulomb exchange near the
production threshold. We recently developed a framework to sum both series of
corrections for the partonic cross section using soft-collinear and
non-relativistic effective theory. If it can be argued that the resummed cross
section approximates the complete result over a significant kinematic range, an
improvement of the hadronic cross section results, even when the production is
not kinematically constrained to the threshold. This is discussed here for the
case of top quark production.Comment: 5 pages, to appear in: Proceedings of the 10th DESY Workshop on
Elementary Particle Theory: Loops and Legs in Quantum Field Theory 2010,
W\"orlitz, Germany, 25-30 Apr 201
BFKL at NNLO
We present a recent determination of an approximate expression for the
O(alpha_s^3) contribution chi_2 to the kernel of the BFKL equation. This
includes all collinear and anticollinear singular contributions and is derived
using duality relations between the GLAP and BFKL kernels.Comment: 8 pages. Talk presented at 12th International Conference on Elastic
and Diffractive Scattering: Forward Physics and QCD, Hamburg, DESY, Germany,
21-25 May 200
Hadronic top-quark pair production with NNLL threshold resummation
We compute the total top-quark pair production cross section at the Tevatron
and LHC based on approximate NNLO results, and on the summation of threshold
logarithms and Coulomb enhancements to all orders with next-to-next-to-leading
logarithmic (NNLL) accuracy, including bound-state effects. We find
\sigma_{t\bar t} = 7.22^{+0.31+0.71}_{-0.47-0.55} pb at Tevatron and
\sigma_{t\bar t} = 162.6^{+7.4+15.4}_{-7.6-14.7} pb at LHC with 7 TeV c.o.m.
energy, for m_t=173.3 GeV. The implementation of joint soft and Coulomb
resummation, its ambiguities, and the present theoretical uncertainty are
discussed in detail. We further obtain new approximate results at N3LO.Comment: 55 pages, LaTeX, 13 figure
Soft radiation in heavy-particle pair production: all-order colour structure and two-loop anomalous dimension
We present a factorization formula for the production of pairs of heavy
coloured particles in hadronic collisions at the production threshold, which
forms the basis for the resummation of soft gluons and Coulomb gluons. We
construct a basis in colour space that diagonalizes the soft function appearing
in the factorization formula to all orders in perturbation theory. This extends
recent results on the structure of soft anomalous dimensions and allows us to
determine an analytic expression for the two-loop soft anomalous dimension at
threshold for all production processes of interest.Comment: 36 pages, LaTeX, 2 figures. v2 matches published version (improved
discussion of NNLL resummation, note added on work by Ferroglia et al.
Single-top t-channel hadroproduction in the four-flavour scheme with POWHEG and aMC@NLO
We present results for the QCD next-to-leading order (NLO) calculation of
single-top t-channel production in the 4-flavour scheme, interfaced to Parton
Shower (PS) Monte Carlo programs according to the POWHEG and MC@NLO methods.
Comparisons between the two methods, as well as with the corresponding process
in the 5-flavour scheme are presented. For the first time results for typical
kinematic distributions of the spectator-b jet are presented in an NLO+PS
approach.Comment: 16+1 pages, 8 figures, matches version accepted for publication in
JHE
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