摘要
本文报告了粲重子Λ_(c)^(+)的四个弱衰变道Λ_(c)^(+)→Λh^(+)和Λ_(c)^(+)→∑^(0)h^(+)(h=K,π)的系列研究.基于在KEKB能量不对称的正负电子对撞机上的Belle探测器收集的980 fb-1数据样本,作者测量了粲重子两体单卡比玻压低(SCS)衰变过程中的直接电荷共轭-宇称(CP)不对称:ACPdir(Λ_(c)^(+)→ΛK^(+))=+0.021±0.026±0.001和ACPdir(Λ_(c)^(+)→∑^(0)K^(+))=+0.025±0.054±0.004;精确测量了衰变不对称参数(α)和其引起的CP不对称度:AC^(α)_(P)(Λ_(c)^(+)→ΛK^(+))=-0.023±0.086±0.071和AC^(α)_(P)(Λ_(c)^(+)→∑^(0)K^(+))=+0.08±0.035±0.14.这是粲重子SCS衰变的第一个AC^(α)_(P)结果;其次,作者在实验上利用粲重子衰变来寻找超子CP破坏,即利用Λ_(c)^(+)→(Λ,∑^(0))π^(+)衰变获得AC^(α)_(P)(Λ→pπ-)=+0.013±0.007±0.011.以上测量均未发现重子CP破坏的证据.此外,该文还报告了Λ_(c)^(+)两个SCS衰变道的分支比测量:B(Λ_(c)^(+)-ΛK^(+))=(6.57±0.17±0.11±0.35)×10^(-4)和B(Λ_(c)^(+)→∑^(0)K^(+))=(3.58±0.19±0.06±0.19)×10^(-4),这些均为目前最精确的结果.
We report a study of Λ_(c)^(+)→Λh^(+)and Λ_(c)^(+)→∑^(0)h^(+)(h=K,π)decays based on a data sample of 980 fb-1 collected with the Belle detector at the KEKB energy-asymmetric e+e-collider.Thefirst results of direct CP asymmetry in two-body singly Cabibbo-suppressed(SCS)decays of charmed baryons are measured,Ad ir CP Λ_(c)^(+)→KK^(+)=+0.021±0.026±0.001 and Ad ir CP Λ_(c)^(+)→∑^(0)K^(+)=+0.025±0.054±0.004.We also make the most precise measurement of the decay asymmetry parameters(a)for the four modes of interest and search for CP violation via the a-induced CP asymmetry(AC^(α)_(P)).We measure AC^(α)_(P) Λ_(c)^(+)→KK^(+)=-0.023±0.086±0.071 and AC^(α)_(P) Λ_(c)^(+)→∑^(0)K^(+)=+0.08±0.35±0.14,which are thefirst AC^(α)_(P) results for SCS decays of charmed baryons.We search for K-hyperon CP violation in Λ_(c)^(+)→K,∑^(0)π^(+)andfind AC^(α)_(P)(K→pπ-)=+0.013±0.007±0.011.This is thefirst time that hyperon CP violation has been mea-sured via Cabibbo-favored charm decays.No evidence of baryon CP violation is found.We also obtain the most precise branching fractions for two SCS Λ_(c)^(+)decays,B Λ_(c)^(+)→KK^(+)=(6.57±0.17±0.11±0.35)×10^(-4)and B Λ_(c)^(+)→∑^(0)K^(+)=(3.58±0.19±0.06±0.19)×10^(-4).Thefirst uncertainties are statistical and the second systematic,while the third uncertainties come from the uncertainties on the world average branching frac-tions of Λ_(c)^(+)→K,∑^(0)π^(+).
基金
supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan
the Japan Society for the Promotion of Science (JSPS)
the Tau-Lepton Physics Research Center of Nagoya University
the Australian Research Council including grants DP180102629, DP170102389, DP170102204, DE220100462, DP150103061, FT130100303
Austrian Federal Ministry of Education, Science and Research (FWF) and FWF Austrian Science Fund No. P 31361-N36
the National Natural Science Foundation of China under Contracts No. 11675166, No. 11705209
No. 11805064
No. 11975076
No. 12135005
No. 12175041
No. 12161141008
Key Research Program of Frontier Sciences, Chinese Academy of Sciencess (CAS), Grant No. QYZDJ-SSW-SLH011
the Shanghai Science and Technology Committee (STCSM) under Grant No. 19ZR1403000
the Ministry of Education, Youth and Sports of the Czech Republic under Contract No. LTT17020
the Czech Science Foundation Grant No. 22-18469S
Horizon 2020 ERC Advanced Grant No. 884719 and ERC Starting Grant No. 947006 ‘‘Inter Leptons” (European Union)
the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft, the Excellence Cluster Universe, and the Volkswagen Stiftung
the Department of Atomic Energy (Project Identification No. RTI 4002)
the Department of Science and Technology of India
the Istituto Nazionale di Fisica Nucleare of Italy
National Research Foundation (NRF) of Korea Grant Nos. 2016R1D1A1B02012900, 2018R1A2B3003643, 2018R1A6A1A060 24970, RS202200197659, 2019R1I1A3A01058933, 2021R1A6A1A03043957, 2021R1F1A1060423, 2021R1F1A1064008, 2022R1A2C 1003993
Radiation Science Research Institute, Foreign Large-size Research Facility Application Supporting project
the Global Science Experimental Data Hub Center of the Korea Institute of Science and Technology Information and KREONET/GLORIAD
the Polish Ministry of Science and Higher Education and the National Science Center
the Ministry of Science and Higher Education of the Russian Federation, Agreement 14.W03.31.0026
the HSE University Basic Research Program, Moscow
University of Tabuk research grants S-1440-0321, S-0256-1438, and S-0280-1439 (Saudi Arabia)
the Slovenian Research Agency Grant Nos. J19124 and P1-0135
Ikerbasque, Basque Foundation for Science, Spain
the Swiss National Science Foundation
the Ministry of Education and the Ministry of Science and Technology of Taiwan
the United States Department of Energy and the National Science Foundation。
