First Measurement of Timelike Compton Scattering

Abstract

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.

Metadata

©2021, American Physical Society. Funding Information: We thank Professors M. Vanderhaeghen, B. Pire, and P. Sznajder for the fruitful exchanges and discussions on the phenomenological aspects of this work and for providing us with the model predictions. We acknowledge the great efforts of the staff of the Accelerator and the Physics Divisions at Jefferson Lab in making this experiment possible. This work is supported in part by the U.S. Department of Energy, the National Science Foundation (NSF), the Italian Istituto Nazionale di Fisica Nucleare (INFN), the French Centre National de la Recherche Scientifique (CNRS), the French Commissariat pour l’Energie Atomique, the UK Science and Technology Facilities Council, the National Research Foundation (NRF) of Korea, the Helmholtz-Forschungsakademie Hessen für FAIR (HFHF), and the Ministry of Science and Higher Education of the Russian Federation. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No. 824093. The Southeastern Universities Research Association (SURA) operates the Thomas Jefferson National Accelerator Facility for the U.S. Department of Energy under Award No. DE-AC05-06OR23177.

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