Abstract
We measure the branching fraction and time-dependent $CP$-violating asymmetry for $B^0\to J/\psi\pi^0$ decays using a data sample of 711 ${\rm fb^{-1}}$ collected on the $\Upsilon(4S)$ resonance by the Belle experiment running at the KEKB $e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(B^0\to J/\psi\pi^0) = [1.62\,\pm 0.11~({\rm stat}) \pm0.07~({\rm syst})]\times 10^{-5}$, which is the most precise measurement to date. The measured $CP$ asymmetry parameters are $\mathcal{S} = -0.59\,\pm 0.19~({\rm stat}) \pm 0.03~({\rm syst})$ and $\mathcal{A} = -0.15\,\pm 0.14~({\rm stat})\,^{+0.04}_{-0.03}~({\rm syst})$. The mixing-induced $CP$ asymmetry ($\mathcal{S}$) differs from the case of no $CP$ violation by 3.0 standard deviations, and the direct $CP$ asymmetry ($\mathcal{A}$) is consistent with zero.
Highlights
We measure the branching fraction and time-dependent CP-violating asymmetry for B0 → J=ψπ0 decays using a data sample of 711 fb−1 collected on the Υð4SÞ resonance by the Belle experiment running at the KEKB eþe− collider
In the process Υð4SÞ → B0B 0, one of the two B mesons can decay into a CP eigenstate fCP at time tCP, while the other can decay into a flavor-specific state ftag at time ttag
The Belle detector is a large-solid-angle magnetic spectrometer consisting of a silicon vertex detector (SVD), a 50-layer central drift chamber (CDC), an array of aerogel threshold Cherenkov counters, a barrel-like arrangement of time-of-flight scintillation counters, and an electromagnetic calorimeter (ECL) comprising CsI(Tl) crystals
Summary
29Advanced Science Research Center, Japan Atomic Energy Agency, Naka 319-1195 30J. Stefan Institute, 1000 Ljubljana 31Institut für Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe 32Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583 33Kennesaw State University, Kennesaw, Georgia 30144 34King Abdulaziz City for Science and Technology, Riyadh 11442 35Department of Physics, Faculty of Science, King Abdulaziz University, Jeddah 21589 36Korea Institute of Science and Technology Information, Daejeon 305-806 37Korea University, Seoul 136-713 38Kyungpook National University, Daegu 702-701 39LAL, Universite Paris-Sud, CNRS/IN2P3, Universite Paris-Saclay, Orsay 40École Polytechnique Federale de Lausanne (EPFL), Lausanne 1015 41P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991 42Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana 43Ludwig Maximilians University, 80539 Munich 44Luther College, Decorah, Iowa 52101 45Malaviya National Institute of Technology Jaipur, Jaipur 302017 46University of Maribor, 2000 Maribor 47Max-Planck-Institut für Physik, 80805 München 48School of Physics, University of Melbourne, Victoria 3010 49University of Mississippi, University, Mississippi 38677 50University of Miyazaki, Miyazaki 889-2192 51Moscow Physical Engineering Institute, Moscow 115409 52Moscow Institute of Physics and Technology, Moscow Region 141700 53Graduate School of Science, Nagoya University, Nagoya 464-8602 54Universitadi Napoli Federico II, 80055 Napoli 55Nara Women’s University, Nara 630-8506 56National Central University, Chung-li 32054 57National United University, Miao Li 36003 58Department of Physics, National Taiwan University, Taipei 10617 59H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342 60Nippon Dental University, Niigata 951-8580 61Niigata University, Niigata 950-2181 62Novosibirsk State University, Novosibirsk 630090 63Osaka City University, Osaka 558-8585 64Pacific Northwest National Laboratory, Richland, Washington 99352 65Panjab University, Chandigarh 160014 66Peking University, Beijing 100871 67University of Pittsburgh, Pittsburgh, Pennsylvania 15260 68Punjab Agricultural University, Ludhiana 141004 69Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198 70University of Science and Technology of China, Hefei 230026 71Showa Pharmaceutical University, Tokyo 194-8543 72Soongsil University, Seoul 156-743 73University of South Carolina, Columbia, South Carolina 29208 74Stefan Meyer Institute for Subatomic Physics, Vienna 1090 75Sungkyunkwan University, Suwon 440-746 76School of Physics, University of Sydney, New South Wales 2006 77Department of Physics, Faculty of Science, University of Tabuk, Tabuk 71451 78Tata Institute of Fundamental Research, Mumbai 400005 79Department of Physics, Technische Universität München, 85748 Garching 80Toho University, Funabashi 274-8510 81Department of Physics, Tohoku University, Sendai 980-8578 82Earthquake Research Institute, University of Tokyo, Tokyo 113-0032 83Department of Physics, University of Tokyo, Tokyo 113-0033 84Tokyo Institute of Technology, Tokyo 152-8550 85Tokyo Metropolitan University, Tokyo 192-0397 86Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 87Wayne State University, Detroit, Michigan 48202 MEASUREMENT OF THE BRANCHING FRACTION AND ... We measure the branching fraction and time-dependent CP-violating asymmetry for B0 → J=ψπ0 decays using a data sample of 711 fb−1 collected on the Υð4SÞ resonance by the Belle experiment running at the KEKB eþe− collider. The branching fraction is measured to be BðB0 → J=ψπ0Þ 1⁄4 1⁄21.62 Æ 0.11ðstatÞ Æ 0.06ðsystÞ × 10−5, which is the most precise measurement to date. The measured
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