Implications for CP asymmetries of improved data on $B\to K^0{\pi }^0$

Abstract

The decay $B^0\to K^0{\pi }^0$, dominated by a $b\to s$ penguin amplitude, holds the potential for exhibiting new physics in this amplitude. In the pure QCD penguin limit one expects $\text{ckp}=0$ and $\text{skp}=\sin 2\beta$ for the coefficients of $\cos \Delta mt$ and $\sin \Delta mt$ in the time-dependent CP asymmetry. Small non-penguin contributions lead to corrections to these expressions which are calculated in terms of isospin-related $B\to K\pi$ rates and asymmetries, using information about strong phases from experiment. We study the prospects for incisive tests of the Standard Model through examination of these corrections. We update a prediction $\text{ckp}=0.15\pm 0.04$, pointing out the sensitivity of a prediction $\text{skp}\approx 1$ to the measured branching ratio for $B^0\to K^0{\pi }^0$ and to other observables.

Comments: Note added, to be published in Physics Letters B