Hamburg 2016 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 59: Top Quark III (tt+X)

T 59.7: Vortrag

Dienstag, 1. März 2016, 18:15–18:30, VMP9 HS

Measurement of the ttγ cross section using dilepton events from the ATLAS experiment at 8 TeV — Nello Bruscino, Markus Cristinziani, Mazuza Ghneimat, •Sebastian Heer, Vadim Kostyukhin, Liza Mijović, Andrea Sciandra, and Kaven Yau Wong — Physikalisches Institut of University of Bonn

The cross section of ttγ production in pp collisions is predicted by the Standard Model and has to be measured by experiment. The measurement presented here is done using ttγ events in the dilepton channel. Dileptonic events were not used for the ttγ process in general yet, because of the small branching fraction. On the other hand, systematic uncertainties are expected to be smaller than in the lepton plus jets channel, due to an excellent signal-to-background ratio.
The analysis uses events from the eµ-channel only, because of the very high signal-to-background ratio, which is not blurred by background processes involving the Z boson. The most dominant background consists of photons radiated by hadrons, e.g. in tt events. The analysis uses a simple cut-and-count method. To get the optimal set of requirements for the measurement, the event selection was optimized by minimizing the relative uncertainty on the expected cross section.
The measurement of the cross section is done using the requirements obtained by the optimization. Due to the high signal-to-background ratio the total uncertainties is only 12%.