Quark/Gluon Discrimination

Abstract

This chapter is dedicated to the specific applications of substructure techniques to discriminate quark-initiated jets from gluon-initiated jets. We begin with a brief discussion on how to tentatively define quark- and gluon-initiated jets. We then concentrate on two broad classes of observables: (i) shape observables like angularities or energy-correlation functions, and (ii) multiplicity-based observables like the iterated soft-drop multiplicity. In each case, we provide a basic analytic understanding of the tools based on the resummation techniques introduced in Chap. 4. We then discuss the key properties of the tools and assess their performance on Monte-Carlo simulations, highlighting the features which are reproduced by the simple analytic calculations.