Measurements of the branching fraction, isospin asymmetry, and lepton-universality ratio in \(B \to J/\psi K\) decays at Belle II

• Published in: arXiv.org 2022-07
• Main Authors: Adamczyk, K, Aihara, H, Aloisio, A, Bansal, S, Becker, J, Behera, P K, Bernieri, E, Bertemes, M, Chekelian, V, Chen, Y Q, Corona, L, de Sangro, R, Dey, S, Doležal, Z, I Domínguez Jiménez, Dong, T V, Epifanov, D, Flood, K, Garcia-Hernandez, M, Garg, R, Gomis, P, Guan, Y, M Hernández Villanueva, Hill, E C, Hollitt, S, Hotta, T, Inami, K, Jia, S, Ketter, C, Kim, Y, Koga, T, Komarov, I, Konno, T, Korpar, S, Kovalenko, E, Krüger, H, Kumar, R, Kumita, T, Kuzmin, A, Kvasnička, P, Y -T Lai, Lalwani, K, Lin, J, Liptak, Z, Liventsev, D, Loos, A, MacQueen, C, McKenna, J A, Mizuk, R, Molina-Gonzalez, N, H -G Moser, Muller, Th, Muroyama, G, Murphy, C, Naruki, M, Ogawa, K, Oskin, P, Paladino, A, Paoloni, E, Parham, K, Passeri, A, Pathak, A, Patra, S, Paul, S, Podesta-Lerma, P L M, A Ramirez Morales, Rasheed, R, Ripp-Baudot, I, Ritzert, M, Rostomyan, A, Rozanska, M, Sanders, D A, Schwartz, A J, Seino, Y, Shillington, T, Soffer, A, Stroili, R, Sumisawa, K, Takahashi, M, Tanaka, S, Taniguchi, N, Taras, P, Torassa, E, Tsuzuki, N, Uehara, S, Unger, K, Unno, Y, Uno, K, Wang, X L, Watanabe, M, Watanuki, S, Wiechczynski, J, Yang, S B, Yin, J H, Yonenaga, M, Yuan, C Z, Zhang, Y, Zhilich, V, Zhou, X Y, Žlebčík, R
• Format: Article
• Language: English
• Subjects: Asymmetry; Channels; Decay; Electrons; Kaons; Leptons; Luminosity; Muons
• ISSN: 2331-8422

We report a study of \(B \to J/\psi(\ell^{+}\ell^{-})K\) decays, where \(\ell\) represents an electron or a muon, using \(e^{+}e^{-}\) collisions at the \(\Upsilon(4S)\) resonance. The data were collected by the Belle II experiment at the SuperKEKB asymmetric-energy collider during 2019-2021, corresponding to an integrated luminosity of \(189\) fb\(^{-1}\). The measured quantities are the branching fractions (\({\mathcal B}\)) of the decay channels \(B^{+} \to J/\psi(e^{+}e^{-})K^{+}\), \(B^{+} \to J/\psi(\mu^{+}\mu^{-}) K^{+}\), \(B^{0} \to J/\psi(e^{+}e^{-}) K^{0}_{S}\), and \(B^{0} \to J/\psi(\mu^{+}\mu^{-})K^{0}_{S}\); the lepton-flavor-dependent isospin asymmetries for the electron [\(A_{I}\left(B \to J/\psi(e^{+}e^{-}) K\right)\)] and muon [\(A_{I}\left(B \to J/\psi(\mu^{+} \mu^{-}) K\right)\)] channels; and the ratios of branching fractions between the muon and electron channels for the charged [\(R_{K^{+}}\left(J/\psi\right)\)] and neutral kaon [\(R_{K^{0}}\left(J/\psi\right)\)] case. The measurements are consistent with the world-average values.