ESTIMATION OF DELTA-GAMMA FOR THE B(S)-(B)OVER-BAR(S) SYSTEM - EXCLUSIVE DECAYS AND THE PARTON MODEL

We estimate DELTAGAMMA for the B(s)-B(s)BAR system by making a sum over exclusive decay modes into ground state mesons, and compare our result to the parton model prediction. For the modes D(s)D(s)BAR, D(s)D(s)*BAR+D(s)*D(s)BAR and D(s)*D(s)*BAR (class I) which give the largest contribution to DELTAGAMMA, we find duality between the exclusive calculation and the parton model in the heavy quark limit with 2m(c)-->m(b) and with the standard factorization assumption, which amounts to exact duality in the N(c)-->infinity limit. In this limit, for the dominant spectator contribution, we find the selection rule GAMMA[B2(CP=-)-->D(s)D(s)*BAR]=0, so that the modes D(s)D(s)*BAR+D(s)*D(s)BAR contribute constructively to DELTAGAMMA, with the same sign as D(s)D(s)BAR (S wave) and D(s)*D(s)*BAR ((S+D)-waves). Most of the modes of class II (psieta, eta(c)phi, psiphi, ...) contribute also constructively to DELTAGAMMA but are suppressed by the effective color factor. On the other hand, from a purely theoretical point of view, we find a rather subtle and interesting difficulty as regards duality in the standard factorization assumption when considering together classes I and II. This unwanted violation of duality could correspond to the well known necessity of correcting this standard factorization assumption. On the basis of both the exclusive and the parton model calculations, we conclude that the sign of DELTAGAMMA is well-defined and its magnitude is stable against theoretical uncertainties. Our estimate gives DELTAGAMMA/GAMMA of the order of 0.15, a value that could be measured at LEP.