Speaker
Description
Decays of the Higgs and Z bosons to bottom quarks are essential for measurements of the bottom quark Yukawa coupling, the Higgs self-coupling, and production modes in highly boosted phase spaces. In ATLAS, these decay products are reconstructed as jets using a clustering radius parameter of R=0.4 and R=1.0 for resolved and boosted decays, respectively. Improvements in flavour tagging, which labels jets as originating from the production of bottom-quark hadrons, have dramatically improved the sensitivity to H->bb and Z->bb decays in recent years by suppressing backgrounds originating from light jets. This talk will summarize the next step in improving analysis sensitivity by applying the transformer architecture to regress the transverse momenta and mass of small- and large-radius jets based on tracks, calorimeter clusters, and leptons within jets. The increase in resonant decay invariant mass resolution is improved up to 30% with respect to the standard jet calibration. The regression models are calibrated in-situ using the method of direct momentum balance in events with jets recoiling against Z->ll or a photon for R=0.4 jets and events targetting Z->bb recoiling against a photon or multiple jets for R=1.0 jets. The jet energy and mass scales for R=1.0 jets in simulation is compared to data. These models therefore offer significant enhancement of resonant X->bb signals that can be directly translated to improvements in physics measurement and search sensitivity.