Study of Negative-Ion TPC Using μ-PIC for Directional Dark Matter Search Tomonori Ikeda, Kentaro Miuch, Atsuhiko Ochi, Ryota Yakabe, Takashi Hashimoto, Ryosuke Taishaku, Daniel P. Snowden-Ifft, Jean-Luc Gauvreau, Toru Tanimori, Atsushi Takada and Kiseki Nakamura EPJ Web Conf., 174 (2018) 02006 Published online: 21 February 2018 DOI: 10.1051/epjconf/201817402006