Evidence for Longitudinal Photon Polarization in Muon-Pair Production by Pions

Abstract

Data on $\ensuremath{\mu}$-pair production by pions are examined as a function of $x$ and ${P}_{T}$ for longitudinal photon polarization. Evidence in the form of a ${{sin}^{2}\ensuremath{\theta}}^{*}$ term in the helicity angular distribution is observed for $x$ near 1. This is conclusive evidence that production in this region is not predominantly through on-shell quark annihilation. The result is consistent with a calculation based on quantum chromodynamics.