Study of η-η^' mixing and sin(2β) at Belle and Belle II

Ming-Chuan Chang^1*

¹應用科學與工程研究所, 輔仁大學, 新北市, Taiwan

* Presenter:Ming-Chuan Chang, email:068190@mail.fju.edu.tw

We have investigated six decay channels: B⁺ → η^(') K^*+, B⁺ → η^(') ρ⁺, and B⁰ → η^(') ω⁰ using signal and background Monte Carlo (MC) simulations from both the Belle and Belle II experiments. The primary goal of this analysis is to measure the branching fractions and CP asymmetry (A_CP) parameters of these decays. Two key motivations drive this study: first, the branching fractions reported in the PDG currently show discrepancies between the results from Belle and BaBar. Second, we now have access to the full Belle data set and Belle II’s Run 1 data, allowing for more precise measurements. This precision is crucial for better understanding η-η^' mixing.

In addition, we study the time-dependent CP violation parameters (A_CP and S_CP) to gain deeper insights into the CKM angle β. Specifically, the sin(2β) parameter can be extracted by analyzing the B⁰ → J/ψ η decay. A time resolution function is derived using the control sample from the B⁰ → J/ψ K_S decay.

The data sample used in these analyses includes an integrated luminosity of 711 fb^-1, corresponding to 771 × 10⁶ BB-bar pairs, collected by the Belle detector at the KEKB asymmetric-energy e⁺e^- collider, with beam energies of 3.5 GeV and 8 GeV. Additionally, we utilize 362 fb^-1 of data, representing 387 × 10⁶ BB-bar pairs, gathered by the Belle II detector between 2019 and 2022 at the SuperKEKB collider, operating at the Υ(4S) resonance with beam energies of 4 GeV and 7 GeV.

Keywords: Belle and Belle II Experiment, CP violation, η-η^' mixing, sin(2β)