Measurement of time-dependent $CP$ violation in $B^0 \to K^0_S \pi^0 \pi^0$ decays

TL;DR

This paper reports the most precise measurement to date of time-dependent $CP$ violation in $B^0 o K^0_S \pi^0\pi^0$ decays, using a large data sample from the Belle experiment, and finds results consistent with the Standard Model.

Contribution

First measurement of $CP$ violation in $B^0 o K^0_S \pi^0\pi^0$ decays with unprecedented precision, using a large dataset from Belle.

Findings

$ ext{sin} 2eta^{ m eff}_1 = 0.92^{+0.27}_{-0.31} ext{(stat)} ext{ and } ext{(syst)}$

$ ext{CP asymmetry } \mathcal{A} = 0.28 ext{ (stat)} ext{ and } ext{(syst)}$

Results are consistent with $b o car{c}s$ decay mode measurements.

Abstract

We report a measurement of time-dependent $CP$ violation in $B^0 \to K^0_S \pi^0 \pi^0$ decays using a data sample of $772 \times 10^6$ $B\bar{B}$ pairs collected by the Belle experiment runnin g at the $\Upsilon (4S)$ resonance at the KEKB $e^+ e^-$ collider. This decay proceeds mainly via a $b\to sd\bar{d}$ "penguin" amplitude. The results are $\sin 2\phi^{\rm eff}_1 = 0.92^{+0.27}_{-0.31}~$ (stat.) $\pm 0.11$ (syst.) and $\mathcal{A} = 0.28 \pm 0.21$ (stat.) $\pm 0.04$ (syst.), which are the most precise measurements of $CP$ violati on in this decay mode to date. The value for the $CP$-violating parameter $\sin 2\phi^{\rm eff}_1$ is consistent with that obtained using decay modes proceeding via a $b\to c\bar{c}s$ "tree" amplitude.