Jet Dipolarity: Top Tagging with Color Flow

84 citations (80 excluding self-citations). Introduced color-flow information as a jet substructure observable, complementing the kinematic variables that dominated the field.

The Key Idea

Most jet substructure variables measure kinematic properties: the masses, momenta, and angular separations of subjets within a fat jet. Dipolarity measures something different: the pattern of soft radiation between two subjets. A color-singlet decay (like W → qq̄) concentrates radiation between the two subjets because the color flow connects them. A color-octet source (like a gluon splitting) radiates outward because the color flow connects each subjet to the beam rather than to each other. Dipolarity quantifies this distinction by computing a p_T-weighted sum of distances from the axis connecting the two subjets.

Incorporated into the HEPTopTagger, dipolarity improves the discrimination between boosted top quarks (which contain a color-singlet W) and QCD jets (which do not) at moderate to high p_T. The observable provides orthogonal information to mass-based and N-subjettiness-based taggers because it probes the color structure of the decay rather than its kinematics.

Recollections

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• DOI
• arXiv:1102.1012
• INSPIRE