On soft gluon emission and the transverse momentum properties of final state particles

We discuss the infrared problem in a theory with confined quarks and gluons. In QED, the infrared cutoff depends on the adjustable experimental energy resolution. For QCD, the physical observables of the asymptotic final state are the hadron momenta whereas the gluon momenta do not correspond to observable quantities. Thus the energy resolution of a “gluon detector” is determined by the hadronic mass scale. In particular, we study the effect of soft gluon emission on the transverse momentum of the hadrons.