On collinearization of quarks in the quark-gluon decays of heavy   orthoquarkonia
  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 probability distributions of quarks and gluons are obtained. The collinear enhancement of the bottomonium decay is shown to take place at the u\={u}--, d\={d} and s\={s}-- pair production and to be absent at the c\={c}-- production. Some other peculiarities of the considered decays are discussed. (Published in Mod.Phys.Lett A 9 (1994) 115). 
A.Ya.Parkhomenko and A.D.Smirnov