Infrared-safe definition of jet flavour

Abstract

It is common, in both theoretical and experimental studies, to separately discuss quark and gluon jets. However, even at parton level, widely-used jet algorithms fail to provide an infrared safe way of making this distinction. We examine the origin of the problem, and propose a solution in terms of a new 'flavour-k t ' algorithm. As well as being of conceptual interest this can be a powerful tool when combining fixed-order calculations with multi-jet resummations and parton showers. It also has applications to studies of heavy-quark jets.

Systematics of quark/gluon tagging

“…This is the strategy adopted in ref. [56]. While this definition neglects the impact of hadronization, it does allow for the calculation of quark jet cross sections at all perturbative orders, including quantum corrections.…”

Quark and gluon jet substructure

“…An algorithm for doing so was proposed by Banfi, Salam, and Zanderighi in [20]. Their idea was to count the number of quarks minus anti-quarks in a jet.…”

Phenomenology of event shapes at hadron colliders

“…This is because the requirement v ≪ 1 forces all radiation to be either soft or collinear. At perturbative level it is also possible to unambiguously attribute a partonic subprocess to the event, for example qq → qq (doing so requires a flavour infrared and collinear safe procedure, as in [72], but the result is JHEP06(2010)038 independent of the choice of the procedure). Here we will use B to label the event's 2 → 2 kinematics and δ to label its 2 → 2 flavour structure.…”

“…We therefore extended it so as to have access to the flavour of both incoming and outgoing partons in the calculation of σ 0 , σ 1 and Σ 1 (v), though not forΣ 2 (v) since its colour-channel separation is not needed for NNLL Σ accuracy. To assign events with more than two outgoing partons to a definite 2 → 2 colour channel we used the exclusive flavour-k t algorithm of [72] to cluster events to a 2 → 2 topology while keeping track of flavour in an infrared safe manner. During the clustering procedure, quarks of different flavour might end up in the same jet, giving rise to multi-flavoured jets, i.e.…”