On Collinearization of Quarks in Quark-Gluon Decays of Heavy   Orthoquarqonia
  The decay of heavy orthoquarkonium into quark-antiquark pair and two gluons is considered. The differential probability of the decay in the tree approximation is calculated and the final quark mass influence on the quark and gluon distribution functions is studied. It is shown that the collinear strengthening of the bottomonium decay probability takes place at the $u \bar u$-, $d \bar d$- and $s \bar s$- pair production and is absent at the $c \bar c$- production. 
A.Ya.Parkhomenko and A.D.Smirnov