The Proton Spin and U(1)-Problem

Abstract

The naive parton interpretation of the famous result of EMC [1] that the total contribution of the quarks to the proton spin $\Delta \Sigma = \sum\nolimits_f {\int {dx(q_f^ + (x)\, - \,q_f^ - (x)\, + \,\tilde q_f^ + (x)\, - \,\tilde q_f^ - (x))} }$is compatible with zero is not only in contradiction with the naive quark model but also with the whole our understanding of baryon spectroscopy. It is because the total spin of the sea quarks and gluons plus orbital momentum must be so large (> 6 !) that it is difficult to understand why the nucleon is the only stable state with J = I = 1/2 [2].