First measurement of timelike Compton scattering

We present the first measurement of the timelike Compton scattering process, γp→p′γ*(γ*→e+e−), obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities 2.25<Q′2<9 GeV2, squared momentum transferred 0.1<−t<0.8 GeV2, and average total center-of-mass energy squared s=14.5 GeV2. The photon beam polarization asymmetry, similar to the beam-spin asymmetry in deep virtual Compton scattering, is sensitive to the imaginary part of the Compton form factors and provides a way to test the universality of the generalized parton distributions. The angular asymmetry of the decay leptons accesses the real part of the Compton form factors and thus the D-term in the parametrization of the generalized parton distributions.