XMASS experiment aims to directly detect the cold dark matter using liquid Xenon (at about -100℃). Dark matter is unknown matter which is 5~6 times quantity of ordinary visible matter in the universe (for more detail). Dark matter plays an imp ortant role to form the present structure of the universe. If the direct detection of the dark matter is achieved, it can be a great help to solve the mysteries of the univ erse and also to discover new particles.
The experimental hall for XMASS was completed in August 2008. The construction of about 800 ton water tank (.FNv10 mx H10 m) to reduce radioactive backg rounds from the outside was finished in autumn same year and The XMASS detector using about 1 ton of liquid xenon was installed in this tank in Oct 2010.
After the commissioning run of XMASS, we refurbished the detector to reduce the background. From autumn 2013, we have started to run our detector.
In future, we will plan to extend to a 20ton multi-purpose detector which will cover not only dark matter also neutrino physics.