Another Look at "Soft" Lepton Pair Production in Nucleon-Nucleon Bremsstrahlung

Abstract

We compare different formalisms for the calculation of lepton pair emission in hadron-hadron collisions and discuss the consequences of the approximations inherent to each of them. Using a Lorentz-covariant and gauge-invariant formalism proposed by Lichard, we calculate lepton pair emission via bremsstrahlung in proton-proton and neutron-proton reactions at energies between 1 and 5 GeV to leading order in the virtual photon four-momentum. These new results suggest that some previous bremsstrahlung calculations based on varieties of the soft-photon approximation might have somewhat overestimated the DLS low-mass dilepton cross sections. We find that the respective intensities of dilepton production through pp and np bremsstrahlung are energy-dependent and become comparable at E kin ≳ 2 GeV. We also calculate the polar angle anisotropy of the lepton spectrum.