Three quark currents and baryon spin

Abstract

We show that three-quark axial currents as required by broken SU(6) spin-flavor symmetry reduce the quark spin contribution to proton spin from ${\Sigma }_p=1$ (one-quark axial current value) to ${\Sigma }_p=0.41(12)$ consistent with the empirical value ${\Sigma }_{p,exp}=0.33(08)$. In the case of the ${\Delta }^{+}(1232)$ baryon, we find that three-quark axial currents increase the one-quark axial current value ${\Sigma }_{{\Delta }^{+}}=3$ to ${\Sigma }_{{\Delta }^{+}}=3.87(22)$. We also calculate the quark orbital angular momenta $L_u$ and $L_d$ in the proton and ${\Delta }^{+}$ and interpret our results in terms of the prolate and oblate geometric shapes of these baryons consistent with their intrinsic quadrupole moments.

Comments: 3 pages, 1 figure, 22nd European Conference on Few-Body Problems in Physics, Cracow 2013