Observation of time-dependent \(CP\) violation and measurement of the branching fraction of \(B^0 \to J/\psi \pi^0\) decays

• Published in: arXiv.org
• Main Authors: Adachi, I, Aloisio, A, Ky, N Anh, Aushev, V, Ayad, R, Bae, H, Bambade, P, Becker, J, Bertacchi, V, Bianchi, F, Biswas, D, Branchini, P, Bussino, S, Campajola, M, M -C Chang, Chen, C, Chilikin, K, H -E Cho, Choudhury, S, Dujany, G, Fillinger, T, Finocchiaro, G, Fodor, A, Gabrielli, A, Godang, R, Graziani, E, Gruberová, Z, Hara, T, Hayashii, H, Higuchi, T, Hohmann, M, Horak, P, Humair, T, Jackson, P, Jacobs, W W, Joo, K K, Junkerkalefeld, H, Kang, S, Kawasaki, T, Kiesling, C, C -H Kim, Koga, T, Korpar, S, Kowalewski, R, Krokovny, P, Kulii, Y, Kumar, D, Kuzmin, A, Y -T Lai, Lam, T, Leboucher, R, Lemettais, C, Y Li, Libby, J, Maiti, R, Marcantonio, D, Martens, A, Miyabayashi, K, Mohanty, G B, Neu, M, Nishida, S, Pakhlova, G, Park, J, S -H Park, Paschen, B, Peschke, R, Pokharel, S, Prell, S, Prim, M T, Prudiiev, I, Raeuber, G, Raiz, S, Reiter, S, Rostomyan, A, Sanders, D A, Schneider, S, Schwanda, C, Selce, A, Serrano, J, Shan, W, J -G Shiu, Shtol, D, Simon, F, Song, W, Stavroulakis, P, Sue, Y, Sumihama, M, Takahashi, M, Tenchini, F, Uchida, M, Unger, K, Urquijo, P, R van Tonder, Veronesi, M, Wallner, S, Wang, X L, Wessel, C, Yelton, J, Zani, L, Zhang, B
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 11.10.2024
• Subjects: Asymmetry; CP violation; Decay; Mesons; Time dependence; Time measurement
• ISSN: 2331-8422

We present a measurement of the branching fraction and time-dependent charge-parity (\(CP\)) decay-rate asymmetries in \(B^0 \to J/\psi \pi^0\) decays. The data sample was collected with the Belle~II detector at the SuperKEKB asymmetric \(e^+e^-\) collider in 2019-2022 and contains \((387\pm 6)\times 10^6\) \(B\overline{B}\) meson pairs from \(\Upsilon(4S)\) decays. We reconstruct \(392\pm 24\) signal decays and fit the \(CP\) parameters from the distribution of the proper-decay-time difference of the two \(B\) mesons. We measure the branching fraction to be \(B(B^0 \to J/\psi \pi^0)=(2.02 \pm 0.12 \pm 0.10)\times 10^{-5}\) and the direct and mixing-induced \(CP\) asymmetries to be \(C_{CP}=0.13 \pm 0.12 \pm 0.03\) and \(S_{CP}=-0.88 \pm 0.17 \pm 0.03\), respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced \(CP\) violation with a significance of \(5.0\) standard deviations for the first time in this mode.