Hidden Structure in a Lagrangian for Hyperfine Splitting of the Heavy   Baryons
  We investigate the hyperfine splitting of the heavy baryons in the bound-state approach. We start with an ordinary relativistic Lagrangian which has been extensively used to discuss finite mass corrections to the heavy limit predictions. It turns out that the dominant contribution arises from terms which do not manifestly break the heavy spin symmetry. The actual heavy spin violating terms are uncovered by carefully performing a 1/M expansion of this Lagrangian. 
Masayasu Harada, Asif Qamar, Francesco Sannino, Joseph Schechter and   Herbert Weigel