Mainz 2014 – scientific programme

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T: Fachverband Teilchenphysik

T 63: Top-Quarks: Paarproduktion

T 63.8: Talk

Tuesday, March 25, 2014, 18:30–18:45, P104

Application of the matrix element method to top quark physics and searches at ATLAS — •Maike Hansen, Philip Bechtle, Ian C. Brock, Klaus Desch, Petra Haefner, and Thomas Velz — Universität Bonn

The matrix element method has proven to yield a very precise measurement of the top quark mass at Tevatron. It is designed to extract the maximum amount of information from each single event. The method is based on a likelihood maximisation. The likelihood function is defined by the probability that a set of measurements results from a certain process (i.e. a top quark decay) given a set of parameters. In the calculation, all possible permutations as well as all possible initial states and the detector resolution are taken into account. This method is also highly promising in searches for new physics where we expect low statistics and therefore need a very precise measurement. Here we benefit from the fact that the full kinematic information is used.

Two applications of the matrix element method were studied: First, a top-quark mass determination on fully-reconstructed ATLAS pseudo data has been performed. Second, the matrix element method has been extended to search for tt resonances in the minimal universal extra dimension (MUED) model. For the tt-resonance search, a likelihood ratio test and a signal fraction measurement based directly on the matrix element likelihood have been performed and tested on simulated events at generator level. As a tt-resonance candidate, a second Kaluza-Klein excitation of the gluon was assumed.