Rescattering and chiral dynamics in [Formula Presented] decay

We examine the role of (Formula presented) decay in the Dalitz plot analysis of (Formula presented) decays, employed to extract the CKM parameter (Formula presented) The (Formula presented) channel is significant because it can break the relationship between the penguin contributions in (Formula presented) (Formula presented) and (Formula presented) decays consequent to an assumption of isospin symmetry. Its presence thus mimics the effect of isospin violation. The (Formula presented) state is of definite (Formula presented) however; we demonstrate that the (Formula presented) analysis can be generalized to include this channel without difficulty. The (Formula presented) or (Formula presented) “meson” is a broad (Formula presented) enhancement driven by strong (Formula presented) rescattering; a suitable scalar form factor is constrained by the chiral dynamics of low-energy hadron-hadron interactions—it is rather different from the relativistic Breit-Wigner form adopted in earlier (Formula presented) and (Formula presented) analyses. We show that the use of this scalar form factor leads to an improved theoretical understanding of the measured ratio (Formula presented).