Berlin 2005 – scientific programme

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T: Teilchenphysik

T 706: Schwere Quarks VIII

T 706.2: Talk

Wednesday, March 9, 2005, 14:15–14:30, TU H2035

QCD multijet background to the muon plus jets channel in top pair production within the DØ experiment — •Yevgeniy Yen, Jenny Böhme, Peter Mättig, and Christian Schmitt — Bergische Universität Wuppertal, Gaußstr. 20, 42097, Wuppertal

The DØ experiment is taking data at a centre-of-mass energy of √s = 1.96 TeV. So far more than five times the previously obtained integrated luminosity from Run I has been received. One of the important issues for the tt cross section measurement and top quark properties is to improve the tt selection in the muon plus jets channel. For optimization studies it is important to have a good description of signal and contributing backgrounds. While signal and W+jets background can be taken from Monte Carlo, the QCD background can not because of uncertertainties in the modelling. Therefore, the QCD sample has to be taken from data using a model independent technique. Two main sources of QCD multijet background to tt production are considered. These are either isolated hadrons faking muons or isolated muons from heavy quark decays. QCD multijet background with isolated hadrons is expected to show a similar topology as heavy quark events with isolated leptons since mass effects become unimportant at high energy. Therefore, muons are replaced by isolated hadrons leading to a QCD background estimate with high statistics even after all top selection cuts. This talk will present the selection of QCD multijet background to the muon plus jets channel in top pair production in Run II at the DØ experiment.