Improving bounds on penguin pollution in B→ππ

In the presence of penguin contributions, the indirect CP asymmetry in B0(t)→π+π− measures sin(2α+2θ), where 2θ parametrizes the size of the penguin “pollution”. We derive a new upper bound on |2θ|, requiring the measurement of BR(B+→π+π0) and an upper bound on B00≡12[BR(B0→π0π0)+BR(B0→π0π0)]. The new bound is stronger than those previously discussed in the literature. We also present a lower bound on B00. Current data may suggest that it is not very small, in which case θ can be determined using a complete isospin analysis.