Charming penguins in B decays

Full expressions of the B-d(0) --> pi(+)pi(-) and B-d(0) --> pi(0) pi(0) amplitudes, given in terms of matrix elements of operators of the effective weak Hamiltonian, are used to study the dependence of the relevant branching ratios on the different contributions, The uncertainty in the extraction of the weak phase alpha from the measurement of the time-dependent asymmetry in B-d(0) --> pi(+)pi(-) decays is also analyzed. We find that, among several effects which may enhance the B-d(0) pi(0) pi(0) branching ratio, the most important is due to ''charming penguin'' diagrams. These diagrams easily increase BR(B-d(0) --> pi(0) pi(0)) up to a value of 1-3 x 10(-6). The same effect produces, however, a large error in the extraction of alpha from the measurement of the B-d(0) --> pi(+)pi(-) time-dependent asymmetry. We show that it is possible to determine charming-penguin amplitudes from the experimental measurement of many decay rates. Their effect is impressive in B+ --> pi(+)K(0) and B-d(0) --> K(+)pi(-) decays, where charming-penguin contributions easily give values of BR(B+ --> pi(+)K(0)) and BR(B-d(0) --> K(+)pi(-)) of about 1 x 10(-5), Among other possibilities, we also suggest to use B-d(0) --> K-0 (K) over bar(0), the BR of which can be as large as 2-3 x 10(-6), to determine the size of charming-penguin amplitudes. (C) 1997 Published by Elsevier Science B.V.