Speaker
Description
The $B^0 \rightarrow K_S^0 \pi^0$ decay is dominated by $b \rightarrow s$ loop amplitudes. Such flavor-changing-neutral current transitions are highly suppressed in the Standard Model and provide an indirect route to search for new physics. This channel is an important cog in the so-called "K\pi puzzle," where the amplitudes of the four $B \rightarrow K\pi$ decays—two neutral modes and two charged modes—are related to each other. The latest studies by Belle II have reduced some of the existing tension in these measurements.
We propose a more detailed study of this channel using the combined Belle + Belle II data, where the former study will be updated with a multivariate analysis (MVA) based approach for $K_S^0$ and $\pi^0$, providing significant room for improvement. For the Belle II data, we will also include the Run II data. This combined dataset is targeted for completion by 2026.
The excellent neutral-particle reconstruction capability of Belle II allows a unique measurement of CP violation asymmetry in this neutral $B$-meson decay channel, serving as an important consistency test of the Standard Model. We perform a measurement of the CP-violating parameters $A$ and $S$, as well as the branching fraction (BF) in $B^0 \rightarrow K_S^0 \pi^0$, using a sample of 772M (Belle) and 387M+ (Belle II) $B\bar{B}$ events recorded in $e^+ e^-$ collisions at a center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance.
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