Development of a Beam Trajectory Monitoring System Using e+/e− Pair Production Events Shota KIMURA, Yusaku EMOTO, Kento FUJIHARA, Hiroshi ITO, Hideyuki KAWAI, Atsushi KOBAYASHI and Takahiro MIZUNO EPJ Web Conf., 170 (2018) 09007 Published online: 10 January 2018 DOI: 10.1051/epjconf/201817009007