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

Understand

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.