Constraining new physics in B0→π+π− with reparametrization invariance and QCD factorization

Usually, B0→π+π− decays are expressed in terms of weak amplitudes explicitly dependent on the CKM weak phase α or γ. In this Letter, we show that the weak amplitudes can be rewritten such that a manifest dependence on β emerges instead. Based on this, we constrain new-physics contributions to the CP-violating phase ϕd in B0-B¯0 mixing. Further, we apply reparametrization invariance and use QCD factorization predictions to investigate the bounds on an additional new-physics amplitude in B0→π+π−.