Additional soft jets in tt-bar production at the Fermilab Tevatron pp-bar collider.

Abstract

A large fraction of top quark events in pp\ifmmode\bar\else\textasciimacron\fi{} collisions at 1.8 TeV will contain additional soft hadronic jets from gluon bremsstrahlung off the quarks and gluons in the hard processes qq\ifmmode\bar\else\textasciimacron\fi{},gg\ensuremath{\rightarrow}tt\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}bb\ifmmode\bar\else\textasciimacron\fi{}${\mathit{W}}^{+}$${\mathit{W}}^{\mathrm{\ensuremath{-}}}$. These extra jets can cause complications when attempting to reconstruct ${\mathit{m}}_{\mathit{t}}$ from the invariant mass of combinations of final-state quarks and leptons. We show how such soft radiation cannot be unambiguously associated with either initial-state radiation or with final-state radiation off the b quarks. The top quarks can radiate too, and in fact the pattern of radiation has a very rich structure, which depends on the orientation of the final-state particles with respect to each other and with respect to the beam. We calculate the full radiation pattern of soft jets in the soft gluon approximation and compare with several approximate forms which are characteristic of parton shower Monte Carlo simulations. The implications for top mass measurements are discussed.