Extracting the quark mixing phase α from Bd0→K0K̄0 decays

We propose a new method for obtaining the CP phase α, based on measurements of Bd0→K0K̄0, along with theoretical input. Because of the similarities of QCD factorization (QCDf) and perturbative QCD (pQCD), this input is basically the same for each of these models. Although the theoretical error is large at present, many of the contributing quantities will be better known in the future, leading to a smaller error. One outstanding question is the extent to which the precision on quark masses, especially mc/mb, can be improved. If one assumes that new physics is not present, the method can be used to predict the values of CP asymmetries in Bd0→K0K̄0: 0.02≤Adir2+Amix2≤0.125. A result outside this range would signal the existence of long-distance effects beyond those included in models of nonleptonic decays based on factorization (such as QCDf and pQCD), or the presence of new physics. © 2007 The American Physical Society.