The Underlying Event in Hard Scattering Processes

Rick Field
(for the CDF Collaboration)

Contribution to Snowmass 2001

October 1, 2001

We study the behavior of the "underlying event" in hard scattering proton-antiproton collisions at 1.8 TeV and compare with the QCD Monte-Carlo models. The "underlying event" is everything except the two outgoing hard scattered "jets" and receives contributions from the "beam-beam remnants" plus initial and final-state radiation. The data indicate that neither ISAJET or HERWIG produce enough charged particles (with PT > 0.5 GeV/c) from the "beam-beam remnant" component and that ISAJET produces too many charged particles from initial-state radiation. PYTHIA which uses multiple parton scattering to enhance the "underlying event" does the best job describing the data.

Zipped Postscript (PS) file (18 pages).

Rick Field - November 1, 2001