Exclusive decay of 1^-- quarkonia and B _c meson into a lepton pair combined with two pions

Abstract.

We study the exclusive decay of $J/\Psi$, $\Upsilon$ and B_c into a lepton pair combined with two pions in two kinematic regions. One is specified by the two pions having large momenta, but a small invariant mass. The other is specified by the two pions having small momenta. In both cases we find that in the heavy quark limit the decay amplitude takes a factorized form, in which the non-perturbative effect related to the heavy meson is represented by a NRQCD matrix element. The non-perturbative effects related to the two pions are represented by some universal functions characterizing the conversion of gluons into pions. Using models for these universal functions and chiral perturbative theory we are able to obtain numerical predictions for the decay widths. Our numerical results show that the decay of $J/\psi$ is of the order of 10^-5 with reasonable cuts and can be observed at BES II and the proposed BES III and CLEO-C. For other decays the branching ratio may be too small to be measured.