b+Jet+MET topology-based physics signatures

Top quark cross section measurement in the missing ET + b-jet channel

Inclusive missing ET + multi-b search

missing ET + 4b analysis

ttH

Jet reconstruction, calibration, and resolution

Jet algorithms

Inputs to jet reconstruction: Calorimeter towers with noise suppression (TopoTowers)

Jet energy resolution improvements using tracks

Jet energy resolution improvements using longitudinal calorimeter segmentation

Jet-Vertex association algorithm

Baseline correction for pile-up and noise

Semi-leptonic b-jet energy scale

Measurement of the jet energy resolution

b-tagging

Track-jet based b-tagging

High pT b-tagging

Event Tagging

Hadronic flavor tagging

gluon bb tagging

highly boosted (bb)-jets

Quark/gluon separation

High Level Trigger b-tagging

INTRODUCTION

Tagging b-jets at the trigger level can expand the physics reach of ATLAS in many ways: it allows to lower the jet ET threshold to increase the acceptance of interesting physics events containing multiple b-jets (like bbH and ttH ), and can be used to reduce non-b backgrounds and improve the purity of Super-symmetry searches involving b-jets in the ?nal state.

The SLAC group has implemented one of the two ATLAS b-tagging algorithms at level 2 trigger: the Impact Parameter ?2 Probability tagger (IPChi2)

Current and future work involves the optimization of the operational parameters of the algorithm, determination of performance in real data events, on-line and off-line validation, and the investigation of new trigger menus involving b-quarks and missing transverse energy for Super-symmetry searches.

LVL2 impact parameter Chi2 algorithm

The IPChi2 tagger is based on the impact parameter distribution of mis-tags, which can be derived directly from data and does not require the use of Monte Carlo templates as in the likelihood ratio b-tagger.

b+MET combined trigger

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Test