The catchment area of jets

Abstract

The area of a jet is a measure of its susceptibility to radiation, like pileup or underlying event (UE), that on average, in the jet's neighbourhood, is uniform in rapidity and azimuth. In this article we establish a theoretical grounding for the discussion of jet areas, introducing two main definitions, passive and active areas, which respectively characterise the sensitivity to pointlike or diffuse pileup and UE radiation. We investigate the properties of jet areas for three standard jet algorithms, k t , Cambridge/Aachen and SISCone. Passive areas for single-particle jets are equal to the naive geometrical expectation πR 2 , but acquire an anomalous dimension at higher orders in the coupling, calculated here at leading order. The more physically relevant active areas differ from πR 2 even for single-particle jets, substantially so in the case of the cone algorithms like SISCone with a Tevatron Run-II split-merge procedure. We compare our results with direct measures of areas in parton-shower Monte Carlo simulations and find good agreement with the main features of the analytical predictions. We furthermore justify the use of jet areas to subtract the contamination from pileup.

Search for supersymmetry in events with four or more leptons ins=8 TeVppcollisions with the ATLAS detector

“…The correction factors are obtained from simulation and are refined and validated using data. An additional correction subtracts the expected contamination from pileup, calculated as a product of the jet area and the average energy density of the event [101]. Events containing jets failing to satisfy the quality criteria described in Ref.…”

Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at $ \sqrt {{{s_{\text{NN}}}}} = {2}{.76}\,{\text{TeV}} $

“…As proposed in [27], the clusters found by the k t algorithm are used to estimate the eventwise background p t -density per unit area, ρ, defined as the median value of the ratio p rec t /A rec for all considered k t -clusters. A rec is the area of the reconstructed cluster in the (η, φ)-plane calculated by the active ghost area method of FastJet [28], with a ghost area of 0.005. To minimize the influence of the track acceptance interval on ρ, only reconstructed clusters with |η| < 0.5 have been used.…”

Multiresolution Jet Reconstruction with FFTJet

“…A reasonable lifetime definition is J α log(s max /s min ). 6 Here, J is the number of preclusters (perhaps, satisfying some imposed selection criteria) present in the clustering tree at each resolution scale s: s min ≤ s ≤ s max . Parameter α can be chosen empirically depending on the process under study (normally 0 < α < 1).…”

“…5 For example, the fraction of events in which the number of reconstructed jets above certain p T threshold equals the number of partons produced at the leading order perturbation theory can be maximized for the signal of interest. 6 More powerful but significantly more complicated definition of the lifetime in the scale space is proposed in [22]. …”

“…However, sequential recombination algorithms are inherently more sensitive to fluctuations in the event energy flow than global methods, and clustering stability properties of sequential recombination algorithms are not fully understood. Changes in the recombination sequence at early clustering stages are not guaranteed to dissipate and may affect clusters obtained at later stages -this artifact led to the introduction of such concepts as "passive" and "active" jet areas which turn out to be distinct [6]. On the other hand, commonly used global reconstructions algorithms -such as seedless iterative cone and its various seeded variations -suffer from another important deficiency inherent in the conebased jet reconstruction.…”