The Proton Spin, Semi-Inclusive processes, and a future Electron Ion Collider

Abstract

We discuss spin physics, Guido Altarelli's contribution to it, and what we still have to learn. We set out in particular a programme for incorporating constraints from semi-inclusive data into global fits of polarized PDFs, and discuss the need for the EIC to increase the precision and kinematic coverage of current measurements.

Comments: Contribution to the volume "From my Vast Repertoire: the Legacy of Guido Altarelli" : 23 pages, 6 figures