Can anyone tell me what the physical meaning of spin-averaged masses is in particle physics?

In a paper I saw that the spin-averaged mass (M_sa) related to the masses of vector (M_v) and pseudoscalar (M_p) mesons, and the relation is: M_sa=(M_p+3M_v)/4 I want to know what spin-average...

04 April 2014 1,180 2 View