Partonic Structure of Light Nuclei

Abstract

In this run group, we propose a comprehensive physics program to investigate the fundamental structure of the 4 He nucleus. An important focus of this program is on the coherent exclusive Deep Virtual Compton Scattering (DVCS) and Deep Virtual Meson Production (DVMP) with emphasis on φ meson production. These are particularly powerful tools enabling model-independent nuclear 3D tomography through the access of partons' position in the transverse plane. These exclusive measurements will give the chance to compare directly the quark and gluon radii of the helium nucleus. Another important measurement proposed in this program is the study of the partonic structure of bound nucleons. To this end, we propose next generation nuclear measurements in which low energy recoil nuclei are detected. The tagging of recoil nuclei in deep inelastic reactions is a powerful technique, which will provide unique information about the nature of medium modifications through the measurement of the EMC ratio and its dependence on the nucleon off-shellness. Finally, we propose to measure incoherent spectator-tagged DVCS on light nuclei (d, 4 He) where the observables are sensitive to the Generalized Parton Distributions (GPDs) of a quasi-free neutron for the case of the deuteron, and bound proton and neutron for the case of 4 He. The objective is to study and separate nuclear effects and their manifestation in GPDs. The fully exclusive kinematics provide a novel approach for studying final state interactions in the measurements of the beam spin asymmetries and the off-forward EMC ratio.At the heart of this program is the Low Energy Recoil Tracker (ALERT) combined with the CLAS12 detector. The ALERT detector is composed of a stereo drift chamber for track reconstruction and an array of scintillators for particle identification. Coupling these two types of fast detectors will allow ALERT to be included in the trigger for efficient † Contact Person: Kawtar Hafidi

The energy-momentum tensor of spin-1 hadrons: formalism

“…More recently, Jefferson Lab has measured deeply virtual π 0 production on the deuteron [42] and a recent letter of intent allows for coherent deuteron DVCS measurements [43]. The latter should also be possible in Hall B using the ALERT detector [44]. Finally, generalized distribution amplitudes (GDAs) for the rho-rho meson pair, accessible in the crossed reaction γ * γ → ρρ [45][46][47], can be related to the rho-meson GFFs similarly to the pion case [12] and could also potentially be studied at Belle II.…”

Nucleon axial form factor from generalized parton distributions

“…Nevertheless, DVCS data-taking will be continued at CERN by the COMPASS Collaboration [34]. The future measurements in Jefferson Lab (JLab) by CLAS Collaboration [35] with experiments starting at 12 GeV (CLAS12) will also provide new information on valence region. Moreover, one of the main goals of future Electron-Ion Collider (EIC) is the measurement of DVCS observables and FFs [36] that makes the extraction of both H and E GPDs possible.…”

Flavor-dependent EMC effect from a nucleon swelling model

“…Another, recently proposed, method to access the flavor dependent structure functions is to detect the low energy recoil nuclei. A program of such measurements using A Low Energy Recoil Tracker (ALERT) combined with the CLAS12 detectors has been approved at JLab [22][23][24]. With the spectator tagged, one knows the type of the nucleon struck by the high energy probe.…”