26-30 July 2021
Europe/Berlin timezone

Calibration of flavour tagging algorithms in ATLAS on ttbar and Z+jets final states

Not scheduled


Poster Top and Electroweak Physics T07: Top and Electroweak Physics




The correct identification of b-initiated jets (b-jets) against c-initiated (c-jets), hadronic tau-initiated (tau-jets) and u-, d-, s-initiated jets (light-jets) is primordial for ATLAS Collaboration searches and precision measurements e.g. ttbar and single-top measurements, supersymmetry, Higgs boson. In consequence, the ATLAS Collaboration has developed several so-called b-tagging algorithms to discriminate b-jets against the other types, trained on ttbar and Z' samples. Expected performance is evaluated on MC events, but due to some inaccuracies in the simulation, it might differ from the performance in real data events. These algorithms are calibrated to account for differences between data and simulated events in the b-tagging efficiency for b-jets and mistagging efficiency in c- and light-jets.

The b-jet efficiency calibration is performed on two-lepton ttbar events in order to exploit the large purity of this final state in b-jets. The c-jet mistag rate is measured on one-lepton
ttbar events, which allow the presence of an hadronically decaying W-jet enriched in c-jets. Both calibrations adopt a combinatorial likelihood approach to retrieve the efficiency of the jet for a given flavour. Finally, due to the large light-jet rejection of b-tagging algorithms, the calibration of light jets mistag rate is performed on a Z+jet sample since ttbar doesn't allow for a pure enough light-jet sample.

This poster presents an overview of the DL1r b-tagging algorithm and the calibration techniques explained above. Results in the form of data-MC scale-factors are obtained for b-efficiency and c- and light-jet mistagging rate with 140 fb^{-1} of data recorded by the ATLAS detector from 2015 to 2018.

Collaboration / Activity ATLAS

Primary authors

Presentation Materials