Melosh rotation: source of the proton's missing spin

Abstract

It is shown that the observed small value of the integrated spin structure\nfunction for protons could be naturally understood within the naive quark model\nby considering the effect from Melosh rotation. The key to this problem lies in\nthe fact that the deep inelastic process probes the light-cone quarks rather\nthan the instant-form quarks, and that the spin of the proton is the sum of the\nMelosh rotated light-cone spin of the individual quarks rather than simply the\nsum of the light-cone spin of the quarks directly.\n