Dresden 2013 – wissenschaftliches Programm
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T: Fachverband Teilchenphysik
T 33: Top-Quarks 1
T 33.8: Vortrag
Montag, 4. März 2013, 12:45–13:00, HSZ-02
Measurement of the Cross Section Ratio of Z/ttbar (8 TeV) / Z/ttbar (7 TeV) with the CMS experiment — •Jan Kieseler — DESY
The possibility of operating the LHC at different beam energies provides the opportunity to study a new class of observables, namely ratios and double ratios of cross sections at different centre-of-mass energies. A large degree of correlation of theoretical systematics in the cross section calculations at different energies leads to a high precision in predictions for such ratios and simultaneously to cancellations of model dependent systematic uncertainties in measurements. In particular, the double ratio of σtt/σZ (8 TeV)/σtt/σZ (7 TeV) in the dileptonic decay channels is studied using the CMS detector. By looking at this double ratio several experimental uncertainties cancel to a large extent. Energy dependent uncertainties are reduced due to similarities in the topologies of the dileptonic tt and Z decay. The correlation of less energy dependent uncertainties further increases the precision when comparing this ratio at different energies. As a result, the improved experimental and theory uncertainties lead to more clear interpretation of the measured results and in turn enhanced sensitivity to physics beyond the Standard Model.