Exponentiation of soft photons in a process involving hard photons

Abstract

We present a simple method of removing the singularities associated with soft photon emission to all orders in perturbation theory through exponentiation, while keeping a consistent description of hard photon emission. We apply this method to the process e+ e- --> mu+ mu- + n photons where we include both Z^0 and photon exchange and retain the muon mass dependence. The photonic radiation is allowed to be radiated off any charged leg, and so we include all initial and final state radiation, as well as all interference effects. The effect of exponentiation is to suppress soft photon emission over the cross-section you would obtain from working at strictly leading order. We also show how one would extend the method to treat the collinear singularity; and remove the associated leading mass logarithms.