Deeply Virtual Compton Scattering on the Neutron with CLAS12 at 11 GeV

Measuring Deeply Virtual Compton Scattering on a neutron target is one of the necessary steps to complete our understanding of the structure of the nucleon in terms of Generalized Parton Distributions (GPDs). DVCS on a neutron target allows to operate a flavor decomposition of the GPDs and plays a complementary role to DVCS on a transversely polarized proton target in the determination of the GPD E, the least known and least constrained GPD that enters Ji’s angular momentum sum rule. To start the experimental program of DVCS on the neutron, we propose to measure beamspin asymmetries for n-DVCS (ed → e′nγ(p)) with the upgraded 11-GeV CEBAF polarized-electron beam and the CLAS12 detector. For the detection of the recoil neutron, necessary to ensure the exclusivity of the reaction after having detected the scattered electron and the DVCS photon, we will construct a scintillator-barrel detector to be placed in the Central Detector, between the CTOF and the solenoid magnet. This Central Neutron Detector (CND) will be made of three layers of scintillator paddles (48 paddles per layer), coupled two-by-two at the front with semi-circular light guides and read at the back by photomultipliers placed outside of the high magneticfield region and connected to the bars via 1-meter-long bent light guides. Simulations and measurements on a prototype, covering one radial layer and two azimuthal bins, have proven the feasibility of this project. In order to provide an accurate mapping of the n-DVCS beam-spin asymmetry over the available 4-dimensional (Q2, xB , −t, φ) phase space, we request 90 days of running on a deuterium target with the maximum available beam energy, 11 GeV.