CHARMLESS B-DECAYS TO ETA' AND ETA

Exclusive charmless B decays to eta' and eta are studied in the standa rd effective Hamiltonian approach. The effective coefficients that tak e into account nonfactorizable effects in external and internal W-emis sion amplitudes are fu;ed by experiment. Factorization is applied to t he matrix elements of QCD, electroweak penguin operators and next-to-l eading corrections to penguin Wilson coefficients, which are renormali zation-scheme dependent, are included, but the resultant amplitude is renormalization-scheme and -scale independent. We show that the unexpe ctedly large branching ratio of B+/---> eta'K+/- measured by CLEO can be explained by the Cabibbo-allowed internal W-emission process b --> c (c) over bar s followed by a conversion of the c (c) over bar pair i nto the eta' via gluon exchanges characterized by a decay constant of order -50 MeV. Implications are discussed. The mechanism of the transi tion c (c) over bar --> eta', if correct, will enhance the decay rates of B --> eta'K by more than an order of magnitude. However, it plays only a minor role to the rare decays B --> eta'(eta)pi(rho) The predi cted branching ratio of B+/---> eta pi(+/-) for positive rho is margin ally ruled out by experiment, indicating that the favored Wolfenstein parameter rho is negative. (C) 1997 Elsevier Science B.V.