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We thanktheKEKBgroup for the excellentoperation of the accelerator; the KEK cryogenics group for the efficient operation of the solenoid; and the KEK computer group, and the Pacific Northwest National Laboratory (PNNL) EnvironmentalMolecular SciencesLaboratory (EMSL) computing group for strong computing support; and the National Institute of Informatics, and Science Information NETwork 5 (SINET5) for valuable network support. We acknowledge support from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS), and the TauLepton Physics Research Center of Nagoya University; the Australian Research Council including Grants No. DP180102629, No. DP170102389, No. DP170102204, No. DP150103061, No. FT130100303; AustrianFederalMinistry ofEducation, Science and Research (FWF) andFWFAustrian Science FundNo. P 31361-N36; theNationalNatural Science Foundation of China under Contracts No. 11435013, No. 11475187, No. 11521505, No. 11575017, No. 11675166, No. 11705209; No. 11761141009; No. 11975076; No. 12042509; No. 12005040; Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS), Grant No. QYZDJSSW-SLH011; the CAS Center for Excellence in Particle Physics (CCEPP); theShanghaiPujiangProgramunderGrant No. 18PJ1401000; 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; Horizon 2020 ERC Advanced Grant No. 884719 and ERC Starting Grant No. 947006 "InterLeptons" (EuropeanUnion); the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft, the Excellence Cluster Universe, and the VolkswagenStiftung; the Department of Atomic Energy (Project Identification No. RTI 4002) and the Department of Science and Technology of India; the Istituto Nazionale di Fisica Nucleare of Italy; National Research Foundation (NRF) of Korea Grants No. 2016R1D1A1B01010135, No. 2016R1D1A1B02012900, No. 2018R1A2B3003643, No. 2018R1A6A1A06024970, No. 2018R1D1A1B07047294, No. 2019K1A3A7A09 033840, No. 2019R1I1A3A01058933; 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, and the HSE University Basic Research Program, Moscow; University of Tabuk research GrantsNo. S-1440-0321, No. S-0256-1438, andNo. S-02801439 (Saudi Arabia); the Slovenian Research Agency Grants No. J1-9124 and No. 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; and the United States Department of Energy and the National Science Foundation. Document

Belle II is a major upgrade of the Belle experiment and operates at the $B$-factory SuperKEKB in Japan. Since the SuperKEKB collider has a design luminosity of 8$\;\times\;$10$^{35}$ cm$^{-2}$s$^{-1}$, about 40 times larger than that of KEKB, Belle II aims to collect 50 ab$^{-1}$ of data over a period of 8 years. The first data taking runs for physics analyses have started in April 2018, with a lower luminosity than the designed one for commissioning purposes. Even with the early dataset, having an integrated luminosity up to 20 fb$^{-1}$, Belle II can improve the current results in the Dark Sector field. In this paper we will present the expected sensitivity of Belle II for invisibly decaying Dark Photons, for Axion-Like Particles and for invisibly decaying $Z^{\prime}$ assuming a $L_{\mu}-L_{\tau}$ model., Comment: 7 pages, 5 figures, BEAUTY 2018, The International Conference on B-Physics at Frontier Machines