Measurement of Time-Dependent $CP$ Violation in $B^0\to \eta'K^0$ Decays

TL;DR

This paper reports the most precise measurement to date of time-dependent $CP$ violation parameters in $B^0 o \\eta'K^0$ decays, confirming consistency with previous results and the Standard Model expectations.

Contribution

First measurement of $CP$ violation parameters in $B^0 o \\eta'K^0$ decays using the full Belle dataset, providing the most accurate values to date.

Findings

Measured $\\sin 2 \phi^{\rm eff}_1 = +0.68 \\pm 0.07 \\pm 0.03$

Measured $\mathcal{A}_{\eta'K^0} = +0.03 \\pm 0.05 \\pm 0.04$

Results are consistent with previous measurements and Standard Model predictions.

Abstract

We present a measurement of the time-dependent $CP$ violation parameters in $B^0\to\eta'K^0$ decays. The measurement is based on the full data sample containing $772\times 10^6$ $B\bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance using the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The measured values of the mixing-induced and direct $CP$ violation parameters are: \begin{align} \sin 2 \phi^{\rm eff}_1 &= +0.68\pm 0.07 \pm 0.03, \nonumber \\ \mathcal{A}_{\eta'K^0} &= +0.03\pm 0.05\pm 0.04, \nonumber \end{align} where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of $\sin 2\phi_1$ measured in $B^0\to J/\psi K^0$ decays.}