Measurement of $CP$ asymmetries in $B^0 \to K^0_S \pi^0 \gamma$ at Belle and Belle II

Sumitted to PubDB: 2025-06-17

Category: Physics / performance paper

Principal Authors	Rishabh Mehta, Gagan Mohanty, Rahul Tiwary
Date	2026-09-27
Working group	Time Dependent CP Violation
Belle II Number	BELLE2-PUB-PH-2025-018
Abstract	We perform a measurement of time-dependent \CP violation parameters in $\Bd \to \KS \piz \g$ decays using a dataset of approximately $770 \times 10^6$ and $550 \times 10^6$ \BBbar pairs collected at the $\Y4S$ resonance by the Belle and Belle~II experiments, respectively. The measured parameters for the combined dataset in the $K^{0}(892)$ dominated region ($M_{\KS\piz} \in [0.8,1.0]\gevcc$) are $\SCP = 0.08 \pm 0.16 \pm 0.02$ and $\CCP = -0.09 \pm 0.08 \pm 0.04$. For the non-$K^{0}(892)$ region ($M_{\KS\piz} \in [1.0,1.8]\gevcc$), the corresponding values are $\SCP = -0.32 \pm 0.33 \pm 0.08$ and $\CCP = -0.07 \pm 0.17 \pm 0.08$. The first quoted uncertainties are statistical, while the second ones are systematic. These results are more precise than previous measurements and consistent with Standard Model predictions.
ArXiv	https://arxiv.org/abs/2606.04496
Journal	JHEP
Preprint Number	2026-6, 2026-10