Relativistic Symmetry Suppresses Quark Spin-Orbit Splitting
  Experimental data indicate small spin-orbit splittings in hadrons. For heavy-light mesons we identify a relativistic symmetry that suppresses these splittings. We suggest an experimental test in electron-positron annihilation. Furthermore, we argue that the dynamics necessary for this symmetry are possible in QCD. 
Philip R. Page, Terry Goldman, Joseph. N. Ginocchio