Probing the nucleon's transversity and the photon's distribution amplitude in lepton pair photoproduction.
We describe a new way to access the chiral-odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. A promising phenomenology of single and double spin observables emerges from the unusual features of this amplitude.
CPhT, Ecole Polytechnique, CNRS, F-91128 Palaiseau, France.
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Szymanowski