Charged Particle Jet Algorithm

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This analysis uses a simple charged particle jet definition that assigns all charged particles to a "jet". The algorithm works will even when a "jet" consists of only a few charged particles. "Jets" are defined as circular regions in eta-phi space with "radius" R = 0.7.
Jet Algorithm:
  • Order all charged particles according to their PT.
  • Start with the highest PT particle and include in the "jet" all particles within the "radius" R = 0.7 (considering each particle in the order of decreasing PT and recalculating the centroid of the jet after each new particle is added to the jet).
  • Go to the next highest PT particle (not already included in a jet) and include in the "jet" all particles (not already included in a jet) within the radius R =0.7.
  • Continue until all particles are in a "jet".
All charged particles with PT > 0.5 GeV/c and |eta| < 1 are considered and the jet radius is allowed to extend outside |eta| < 1. The figure illustrates an event with six charged particles and five "jets". The transverse momentum of the "jet" is defined to be the scalar PT sum of all the particles within the "jet", where PT is measured with respect to the beam axis. The charged particle "jets" are ordered according to their transverse momentum with PTJ1 being the transverse momentum of the leading (highest transverse momentum) "jet". In general, observables depend on the definition of a "jet" and it is important to apply the same definition to both the QCD Monte-Carlo Models and the data.