Fuzzy Jets

While some particles can be identified by their type, such as electrons [3, 4] and muons [5, 6], most of the detected particles are light hadrons produced in collimated sprays called jets. Jets are the consequence of high energy quarks or gluons fragmenting into colorless hadrons. Experimentally, jets are defined by clustering schemes which group together measured calorimeter energy deposits or reconstructed charged particle tracks. A jet algorithm is a clustering scheme that connects the measured objects with theoretical quantities that can be calculated and simulated. At a hadron collider, the natural coordinates for describing particles arep T, y, and φ, where p T is the magnitude of the momentum transverse to the proton beam,y is the rapidity, andφ is the azimuthal angle. Particles or calorimeter energy deposits are clustered using jet algorithms based on distance metrics on their coordinates in (p T, ρ) (p T,y,φ) . In order for a jet algorithm to be useful to experimentalists and theorists, the collection of jets should be IRC safe in the following sense: 1. Infrared safe (IR): if a particlei is added with p T 0, the jets are unaffected.