Measurement of CP asymmetries in $B^0 \to K^0\pi^0$ decays

TL;DR

This paper reports measurements of CP violation parameters and branching fractions in B0 to K0 pi0 decays, providing insights into CP asymmetries and testing isospin sum rules with a large data sample from the Belle experiment.

Contribution

First measurement of CP violation parameters in B0 to K0 pi0 decays using Belle data, testing isospin sum rule deviations.

Findings

Measured sin 2φ1^eff = +0.67 ± 0.31 (stat) ± 0.08 (syst)

Measured direct CP asymmetry A_{K^0 π^0} = +0.14 ± 0.13 (stat) ± 0.06 (syst)

Branching fraction B(B0 → K0 π0) = (8.7 ± 0.5 (stat) ± 0.6 (syst))×10^{-6}

Abstract

We report measurements of CP violation parameters in $B^0 \to K^0 \pi^0$ decays based on a data sample of $657 \times 10^6 B\bar{B}$ pairs collected with the Belle detector at the KEKB $e^+ e^-$ asymmetric-energy collider. We use $B^0 \to K^0_S \pi^0$ decays for both mixing-induced and direct $CP$ violating asymmetry measurements and $B^0 \to K^0_L \pi^0$ decays for the direct CP violation measurement. The CP violation parameters obtained are $\sin 2 \phi_1^{\rm eff} = +0.67 \pm 0.31{(stat)} \pm 0.08 {(syst)}$ and $\mathcal{A}_{K^0 \pi^0} = +0.14 \pm 0.13{(stat)} \pm 0.06 {(syst)}$. The branching fraction of $B^0 \to K^0 \pi^0$ decay is measured to be $\mathcal{B}(B^0 \to K^0 \pi^0) = (8.7\pm0.5 (\rm{stat.})\pm0.6 (\rm{syst.}))\times 10^{-6}$. The observed $\mathcal{A}_{K^0 \pi^0}$ value differs by 1.9 standard deviations from the value expected from an isospin sum rule.