Exclusive decay of 1(--) heavy quarkonium into photon and two pions

We study the exclusive decay of 1(--) heavy quarkonium into one photon and two pions in the kinematic region, where the two-pion system has a invarian t mass which is much smaller than the mass of heavy quarkonium. Neglecting effects suppressed by the inverse of the heavy quark mass, the decay amplit ude can be factorized, in which the nonperturbative effect related to heavy quarkonium is represented by a non-relativistic QCD matrix element, and th at related to the two pions is represented by a distribution amplitude of t wo gluons in the isoscalar pion pair. By taking the asymptotic form for the distribution amplitude and by using chiral perturbative theory we are able to obtain numerical predictions for the decay. Numerical results show that the decay of J/psi can be observed at BEPC and at CESR. Experiment observa tion of this process in this kinematic region at BEPC and CESR can provide information about how gluons are converted into the two pions and may suppl y a unique approach to study I = 0 s-wave pi pi scattering. (C) 2001 Publis hed by Elsevier Science B.V.