Measurement of $CP$ asymmetries in $B^0 \to \eta' K_S^0$ decays at Belle II

Abstract We describe a measurement of charge-parity ($CP$) violation asymmetries in $B^0\to\eta'K^0_S$ decays using Belle II data. We consider $\eta'\to\eta(\to\gamma\gamma)\pi^+\pi^-$ and $\eta'\to\rho(\to\pi^+\pi^-)\gamma$ decays. The data were collected at the SuperKEKB asymmetric-energy $e^+e^-$ collider between the years 2019 and 2022, and contain $(387\pm 6) \times 10^6$ bottom-antibottom meson pairs. We reconstruct $829\pm35$ signal decays and extract the $CP$ violating parameters from a fit to the distribution of the proper-decay-time difference between the two $B$ mesons. The measured direct and mixing-induced $CP$ asymmetries are $\text{C}_{\eta'K^0_S} = -0.19 \pm 0.08 \pm 0.03 $ and $\text{S}_{\eta'K^0_S} = +0.67 \pm 0.10 \pm 0.04 $, respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions.
Tags
Working group Time Dependent CP Violation
Principal authors @  Hanwook Bae, Jakub Kandra, Stefano Lacaprara
Reference Phys.Rev.D 110, 112002 (2024), DOI: 10.1103/PhysRevD.110.112002
Document BELLE2-PUB-PH-2023-011
Links arXiv:2402.03713, Inspire, PRD
Bibtex 
@article{Belle-II:2024xzm,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Measurement of CP asymmetries in B0{\textrightarrow}{\ensuremath{\eta}}'KS0 decays at Belle II}",
    eprint = "2402.03713",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2024-003, KEK Preprint 2023-50",
    doi = "10.1103/PhysRevD.110.112002",
    journal = "Phys. Rev. D",
    volume = "110",
    number = "11",
    pages = "112002",
    year = "2024"
}