I set out to search for the particle side of dark matter, one of the most important open questions in modern physics. My work is carried out with the world’s largest single-phase scintillation liquid Xenon dark matter detector, named XMASS, located in Kamioka in Japan. If it exists, the dark matter signature from the detector will be extremely rare. At the heart of this experiment is the production of a supreme low radiation environment to a level not found anywhere in nature. I am also enthusiastic about free and open source software and hardware, together with their applications in physics experiments and the real world.