NONFACTORIZABLE CONTRIBUTIONS TO NONLEPTONIC WEAK DECAYS OF HEAVY MESONS

Nonfactorizable contributions to exclusive two-body nonleptonic weak decays of heavy mesons arising from color octet currents, characterized by the parameter r2, are extracted from the data. It is found that r2 is equal to approximately -0.67, -(0.9-1.1), -(1.2-1.3), approximately 0.36 respectively for D --> KBARpi, KBAR*pi, KBAR*rho, BBAR --> Dpi decays. As expected, soft-gluon effects become stronger when the decay particles are less energetic, allowing more time for significant final-state strong interactions. As a consequence, the parameter a2 is not universal and is channel or class dependent, contrary to the anticipation of the factorization approach. The leading 1/N(c) expansion works most successfully for D --> KBARpi decays as the subleading 1/N(c) factorizable contribution is almost compensated by the soft-gluon effect. We argue that, in contrast to what happens in B- --> D(*) pi(rho) decays, the nonfactorizable term and the subleading 1/N(c) factorizable term in BBAR --> psiKBAR(*) decays are opposite in signs, in accordance with a recent QCD sum rule calculation. Implications are discussed.