Does a transverse energy trigger actually trigger on large- PT jets?

Abstract

The problems raised by the interpretation of the data of the NA5 experiment (reportedly contradicting evidence for large- p T jets) are reconsidered in the light of a recent suggestion made by G.C. Fox about the importance of gluon bremsstrahlung off the initial (colliding) partons. For this sake a full Monte Carlo program for hadron-hadron interactions at large p T has been set up which includes, besides the QCD hard scattering process and the fragmentation à la Field and Feynman of the final quanta, also QCD radiation off the initial and final quanta and beam jet fragmentation. We find that gluon bremsstrahlung off initial partons is quite important at collider energies. But at the energy of the NA5 experiment it is too scarce to be of any (qualitative) consequence. Rather, we find that hadrons from the two beam jets sizably contribute to the transverse energy E T even at quite large values of E T and that the resulting event structure completely depends on the model chosen for the beam jets. In particular, if the latter satisfies KNO scaling large E T is found to select purely soft and not hard scattering events, contrary to what one naively expects.