We report a measurement of the mixing-induced and direct $\textit{ CP}$ violation parameters $S_{ \text{ CP}}$ and $A_{ \text{ CP}}$ from $B^0 \to J/\psi K^0_S$ decays reconstructed by the Belle II experiment at the SuperKEKB asymmetric-energy electron-positron collider. The data, collected at the center-of-mass energy of the $\Upsilon(4S)$ resonance, correspond to $190\text{ fb}^{ -1}$ of integrated luminosity. We measure ${ S_{ \text{ CP}} = 0.720\pm0.062\pm0.016}$ and $A_{ \text{ CP}} = 0.094\pm0.044^{ +0.042}_{ -0.017}$, where the first uncertainties are statistical and the second systematic. In the Standard Model, $S_{ \text{ CP}}$ equals $\sin(2\phi_1)$ to a good approximation.
Categories: hep-ex