Non-Spherical Shapes of the Proton: Existence, Measurement and Computation

Understand

The nature of the proton wave function can be elucidated by studying the matrix elements of spin-dependent quark density operators SDDs, defined as matrix elements of density operators in proton states of definite spin-polarization.

• These have an infinite variety of non-spherical shapes.
• The matrix elements of the SDDs are closely related to specific transverse momentum dependent TMD parton distributions accessible in the angular dependence of certain semi-inclusive processes.
• New measurements would allow the direct exhibition of the non-spherical nature of the proton.