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T: Fachverband Teilchenphysik

T 65: Experimentelle Methoden II

T 65.8: Vortrag

Mittwoch, 27. März 2019, 17:45–18:00, S01

Measuring the Jet Energy Resolution with the Bisector Method in ATLAS — •Tanja Holm and Ian C. Brock — Physikalisches Institut Universität Bonn, Bonn, Germany

Jets play an important role in many physics processes at the LHC. Therefore a precise knowledge of its jet energy resolution (JER) is important. It is defined as the width of the energy distribution of a reconstructed jet with respect to its true energy.
The bisector method is one way of estimating the JER. It is a geometric approach to separate particle-level from detector-level contributions to the transverse momentum imbalance in dijet events. Additionally out-of-cone mis-measurements of the jet energy due to the jet reconstruction algorithm are subtracted. Particle-level imbalances mostly originate from initial-state radiation and therefore are expected to be isotropic in the transverse plane. Detector-level imbalances only occur in the direction of the jets. For this reason the imbalance vector is decomposed into a perpendicular and a parallel component with respect to the average direction of the jets ("jet axis"). The resolution effects perpendicular to the jet axis (particle level) are removed from the resolution effects parallel to the jet axis (particle + out-of-cone effects + detector level). The resolution of the out-of-cone effects gets evaluated in Monte Carlo samples and is subtracted quadratically, remaining therefore with the resolution originating from the detector. This talk will discuss the bisector method, its implementation and improvements for Run 2 of the LHC at ATLAS.