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  • Measurement of $CP$ asymmetries in $B^0\to\eta'K^0_s$ decays at Belle II
    Adachi, I; Aloisio, A; Asner, D. M; Aushev, V; Bahinipati, S; Bambade, P; Beaubien, A; Bertacchi, V; Bianchi, F; Bilokin, S; Biswas, D; Bussino, S; Campajola, M; Cao, L; Casarosa, G; Cecchi, C; Cerasoli, J; Chang, M. -C; Corona, L; De La Motte, S. A; Dong, T. V; Dorigo, M; Dujany, G; Eliachevitch, M; Ferber, T; Ferlewicz, D; Fillinger, T; Finocchiaro, G; Fodor, A; Forti, F; Frey, A; Gabrielli, A; Ganiev, E; Giordano, R; Godang, R; Grammatico, T; Greenwald, D; Gruberová, Z; Hayashii, H; Hearty, C; Heidelbach, A; Hoek, M; Humair, T; Jin, Y; Junkerkalefeld, H; Kaliyar, A. B; Kang, S; Kim, D. Y; Kim, K. -H; Kodyš, P; Koga, T; Kunigo, T; Lai, Y. -T; Libby, J; Maiti, R; Martellini, C; Masuda, M; Metzner, F; Miller, C; Mirra, M; Moneta, S; Mussa, R; Nakamura, I; Natochii, A; Nayak, M; Ogawa, S; Pakhlova, G; Parham, K; Park, S. -H; Patra, S; Paul, S; Peschke, R; Piilonen, L. E; Pokharel, S; Raiz, S; Reiter, S; Robertson, S. H; Sanders, D. A; Sandilya, S; Sato, Y; Schwanda, C; Seino, Y; Senyo, K; Shan, W; Shillington, T; Skorupa, J; Sokolov, A; Stroili, R; Svidras, H; Takizawa, M; Tanaka, S; Uno, S; Ushiroda, Y; Vahsen, S. E; van Tonder, R; Wakai, M; Wang, Z; Watanuki, S; Won, E; Zhukova, V. I

    02/2024
    Journal Article

    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.

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