The Spin--Symmetry of the Quark Model
  Corrections to the exact heavy--quark symmetry results are expected to follow the $1/m_{Q}$ mass effect of the heavy--quark. We show, by an explicit calculation, that there is something other than the mass effect that suppresses the breaking of the spin symmetry. 
Patrick J. O'Donnell, Q.P. Xu and Humphrey K.K. Tung