4,397 research outputs found
Extending the Matrix Element Method beyond the Born approximation: Calculating event weights at next-to-leading order accuracy
In this article we illustrate how event weights for jet events can be
calculated efficiently at next-to-leading order (NLO) accuracy in QCD. This is
a crucial prerequisite for the application of the Matrix Element Method in NLO.
We modify the recombination procedure used in jet algorithms, to allow a
factorisation of the phase space for the real corrections into resolved and
unresolved regions. Using an appropriate infrared regulator the latter can be
integrated numerically. As illustration, we reproduce differential
distributions at NLO for two sample processes. As further application and proof
of concept, we apply the Matrix Element Method in NLO accuracy to the mass
determination of top quarks produced in e+e- annihilation. This analysis is
relevant for a future Linear Collider. We observe a significant shift in the
extracted mass depending on whether the Matrix Element Method is used in
leading or next-to-leading order.Comment: 35 pages, 12 figures, references & acknowledgments added, typos
corrected, matches published versio
Polarization and spin correlations of top quarks at a future e+ e- linear collider
We discuss the polarization and spin correlations of top quarks produced
above threshold at a future linear collider, including QCD radiative
corrections.Comment: 11 pages (LaTeX), 16 Postscript figure. Contribution to the
International Workshop on "Symmetry and Spin", PRAHA-SPIN99, Prague, Czech
Republic, September 5 -12, 199
The spin density matrix of top quark pairs produced in electron-positron annihilation including QCD radiative corrections
We calculate the spin density matrix of top quark pairs for the reaction
to order . As an application we show
next-to-leading order results for a variety of spin observables for the
system. These include the top quark and antiquark polarizations and
spin-spin correlations as a function of the center-of-mass energy
and of the top quark scattering angle for arbitrary longitudinal polarization
of the electron/positron beam.Comment: 26 pages, 13 Postscript figures, uses REVTE
Kira - A Feynman Integral Reduction Program
In this article, we present a new implementation of the Laporta algorithm to
reduce scalar multi-loop integrals---appearing in quantum field theoretic
calculations---to a set of master integrals. We extend existing approaches by
using an additional algorithm based on modular arithmetic to remove linearly
dependent equations from the system of equations arising from
integration-by-parts and Lorentz identities. Furthermore, the algebraic
manipulations required in the back substitution are optimized. We describe in
detail the implementation as well as the usage of the program. In addition, we
show benchmarks for concrete examples and compare the performance to Reduze 2
and FIRE 5.
In our benchmarks we find that Kira is highly competitive with these existing
tools.Comment: 37 pages, 3 figure
- …