Speaker
Description
Generalized Parton Distributions (GPDs) describe correlations between the longitudinal momentum and the transverse position of the partons inside the nucleon . GPDs have been studied in many experiments worldwide mainly using Deeply Virtual Compton Scattering (DVCS, ep → e’p’γ).
This talk will highlight the measurement of the time-reversal conjugate process of DVCS, Timelike Compton Scattering (TCS). TCS on the proton (γp → γ*p’ → e⁺e-p’ ) is the photoproduction of a virtual timelike photon, which then decays into a lepton pair. Experimental studies of DVCS and TCS are complementary. Indeed, beam and target spin asymmetries for DVCS give direct access to the imaginary part of combinations of Compton Form Factors (CFFs, which are related to GPDs), whereas the angular asymmetries of the decay lepton pairs in TCS allow to access primarily the real parts of CFFs. The experimental measurement of the TCS angular asymmetry will provide new information on the real part of GPDs, which is less constrained by existing DVCS data than the imaginary part.
The upgraded CEBAF accelerator and the recently constructed CLAS12 detector of Jefferson Lab provide the ideal setting to perform a TCS experiment CLAS12 took data with a 10.6 GeV electron beam impinging on a liquid-hydrogen target in the spring and fall of 2018. This talk will assess the current status of the analysis of CLAS12 data and present preliminary results for TCS.
