Can angular momentum of quarks and gluons in the proton be observed?

Simonetta Luitti (UVa)

Describing the quark and gluon angular momentum decomposition into its spin and orbital components requires accessing the particles' transverse degrees of freedom in both momentum and position relative to the proton center of mass. As a consequence, the observables for the orbital components consistent with the CPT symmetries of the theory, need to be defined beyond the standard available set from semi-inclusive scattering processes. Starting from a new method to derive the angular momentum decomposition, I will give an overview of the main issues, illustrating specific aspects for both longitudinal and transverse polarization.