Charged jet evolution and the underlying event in proton-antiproton collisions at 1.8 TeV

The growth and development of " charged particlejets" produced in proton- antiprotoncollisions at 1.8 TeV are studied over a transversemomentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transversemomentum) charged jet observables are compared with the QCD Monte Carlo models HERWIG, ISAJET, and PYTHIA. The models describe fairly well the multiplicity distribution of charged particleswithin the leading charged jet, the size of the leading charged jet, the radial distribution of charged particlesand transversemomentum around the leading charged jet direction, and the momentum distribution of charged particleswithin the leading charged jet. The direction of the leading " charged particlejet" in each event is used to define three regions of eta-phi space. The "toward" region contains the leading " charged particlejet," while the "away" region, on the average, contains the away-side jet. The " transverse" region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to the " underlying event" component of the QCD Monte Carlo models. HERWIG, ISAJET, and PYTHIA with their default parameters do not describe correctly all the properties of the " transverse" region.