Heidelberg 2007 – scientific programme

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T: Fachverband Teilchenphysik

T 512: QCD Experiment III

T 512.4: Talk

Friday, March 9, 2007, 14:45–15:00, INF 327 SR 2

Studying QCD Jet Production in W / Z + Jet events at D0, Tevatron — •Henrik Nilsen — Rosastrasse 21, 79098 Freiburg

During the last few years there has been a major development in how to describe emissions of QCD jets in Monte Carlo event generators. Traditionally a parton shower (PS) approach has been used to generate QCD (initial/final state) radiation. While accurate for low pT emissions, it is well know that it does not offer a good description of high pT emissions and angular corrolations.

An alternative to a PS is to include all QCD emissions in the matrix element. To get reliable results in all regions of phase space one must include virtual corrections, but this leads to prohibitively difficult calculations. However, by ignoring the virtual corrections one still gets a good description of hard, well separated emissions.

The Catani-Krauss-Kuhn-Webber (CKKW) algorithm (ref.1), implemented in the event generator SHERPA (ref.2), uses PS for soft/colinear emissions combined with tree level matrix element computations for hard/well separated emissions. A continuous transition between the two methods is an intrinsic property of the algorithm.

SHERPA has been found to perform very well on a theoretical level, but the ultimate test is obviously to compare it`s predictions to experimental data.

We have performed a comparison between data from the D0 experiment at Tevatron, Fermilab, and SHERPA, as well as Pythia (ref.3) and Alpgen (ref.4), in the channels Z(->ee)+jets and W(->enu)+jets.