Particle flow jets in the t anti t l+jets channel in ATLAS

The ATLAS particle flow algorithm combines tracking and calorimeter information to achieve an improved resolution for jets and missing transverse momentum. Studies based on 8 TeV ATLAS data have shown improvements for the energy response and jet angular resolution. Additionally the pile-up contribution is considerably reduced. Jets stemming from b-quarks are important for top-quark and Higgs boson physics as well as for searches for new physics. Particle flow inherently adds tracker information to the jets and thus could allow improvements of the b-jet performance. This contribution presents the studies done using t anti t events in the l+jets channel at 13 TeV in ATLAS. The t anti t topology is advantageous, due to its clean signature and a large fraction of b-jets from the top-quark decays. The invariant mass distributions of the hadronically decaying W boson and top-quark are used to investigate the performance of particle flow jets in comparison to jets based only on calorimeter information. The calibration of the jet collection, which is the first step after the jet reconstruction, has been slightly modified for particle flow due to the different nature of the jets. A further emphasis is placed on properties of b-jets (e.g. the b-hadron decay mode and the decay multiplicity) within particle flow, which could allow the jet energy scale and jet energy resolution as well as b-tagging efficiencies to be further improved.