Abstract
We introduce soft drop isolation, a new photon isolation criterion inspired by jet substructure techniques. Soft drop isolation is collinear safe and is equivalent to Frixione isolation at leading non-trivial order in the small R limit. However, soft drop isolation has the interesting feature of being democratic, meaning that photons can be treated equivalently to hadrons for initial jet clustering. Taking advantage of this democratic property, we define an isolated photon subjet: a photon that is not isolated from its parent jet but is isolated within its parent subjet after soft drop declustering. The kinematics of this isolated photon subjet can be used to expose the QED splitting function, in which a quark radiates a photon, and we verify this behavior using both a parton shower generator and a perturbative calculation in the collinear limit.
Highlights
In this paper, we introduce a new substructure-based photon isolation technique called soft drop isolation
We introduce soft drop isolation, a new photon isolation criterion inspired by jet substructure techniques
8We performed a study using R0 = R in the soft drop isolation criterion; this version of the criterion does lead to sensible results, we found it to be more sensitive to non-perturbative hadronization effects
Summary
Soft drop isolation is based on soft drop declustering, a jet grooming algorithm that removes soft and wide-angle radiation to find hard substructure [37]. We show how to tag isolated photons by identifying jets without any substructure.
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