Karlsruhe 2011 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

T: Fachverband Teilchenphysik

T 11: QCD (Theorie) II

T 11.6: Talk

Thursday, March 31, 2011, 18:00–18:15, 30.23: 10-1

Numerical NLO QCD calculations - Subtraction method for the virtual contributions — •Christian Reuschle — Institut für Physik, Universität Mainz, D-55099 Mainz, Germany

This talk reports on a previously published algorithm for the numerical calculation of one-loop QCD amplitudes. The algorithm consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of one-loop amplitudes and a method to deform the integration contour for the loop integration into the complex space. It is formulated at the amplitude level and does not rely on Feynman graphs. Therefore all required ingredients can be calculated efficiently using recurrence relations.

The talk will concentrate on the subtraction terms by first reviewing the dipole subtraction method for the real emission contributions of a next-to-leading order QCD calculation and then showing how this is extended to the virtual contributions, i.e. the one-loop QCD amplitudes. It will be discussed how to derive local subtraction terms for the soft, the collinear and the ultraviolet regions of the one-loop integration and that these can be formulated on the amplitude level rather than on a Feynman diagrammatic level. This allows one to efficiently implement the subtraction terms using recurrence relations, in order to construct one-loop integrands which are locally finite and can be integrated numerically. Examples of standard QCD processes will be considered in order to demonstrate the validity of the method.