Abstract
Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe $n$-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community---boosted top tagging, boosted $W/Z/H$ tagging, and quark/gluon discrimination---we use power-counting techniques to identify three new series of powerful discriminants: $M_i$, $N_i$, and $U_i$. The $M_i$ series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The $N_i$ series behave parametrically like the $N$-subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the $U_i$ series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.
Highlights
With the Large Hadron Collider (LHC) rapidly acquiring data at a center-of-mass energy of 13 TeV, jet substructure observables are playing a central role in a large number of analyses, from Standard Model measurements [1,2,3,4,5,6,7,8,9,10,11,12] to searches for new physics [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34]
As the field of jet substructure matures [35,36,37,38], observables are being designed for increasingly specific purposes, using a broader set of criteria to evaluate their performance beyond raw discrimination power
The generalized energy correlation functions allow us to introduce a wide variety of new substructure observables, though we focus on three series with nice properties
Summary
With the Large Hadron Collider (LHC) rapidly acquiring data at a center-of-mass energy of 13 TeV, jet substructure observables are playing a central role in a large number of analyses, from Standard Model measurements [1,2,3,4,5,6,7,8,9,10,11,12] to searches for new physics [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34].1 As the field of jet substructure matures [35,36,37,38], observables are being designed for increasingly specific purposes, using a broader set of criteria to evaluate their performance beyond raw discrimination power. We exploit the known properties of IRC safe observables to systematically identify a useful basis for jet substructure, which we call the generalized energy correlation functions. These observables—denoted by ve(nβ) and defined in Eq (3.3)—are an extension of the original energy correlation functions with a more flexible angular weighting.. – Ui: A new series of observables for quark/gluon discrimination which probes the structure of multiple soft gluon emissions from the hard jet core, leading to improved performance over the standard C1 observable [74].
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