Penguin Pollution in B->pi pi

Abstract

In the presence of penguin contributions, the indirect CP asymmetry in B0(t)->pi+ pi- measures some effective (``polluted'') angle 2alpha_{eff}. The angle 2theta=2alpha_{eff}-2alpha, parameterizes the size of the penguin pollution. A new, most stringent upper bound on |2theta|, requiring the measurement of of BR(B+ -> pi+ pi0) and an upper bound on B00 \equiv {1\over 2} [BR(B0 -> pi0 pi0) + BR(B0bar -> pi0 pi0)] is discussed. An interesting consequence of this bound, is a lower limit on B00. The summer update of the branching ratios and asymmetries in B->pi pi modes is expected to provide a more precise picture of the size of penguin pollution.