XMASS is an acronym for Xenon MASSive detector for dark matter searches. The detector is located underground in Hall C of the Kamioka Observatory. Its active volume contains 834 kg of liquid xenon and is kept at minus 100 degree Celsius. 642 2-inch Hamamatsu R10789 photomultipler tubes record the scintillation light output from interactions of a dark matter particle inside that active volume. The detector is located inside of an active muon veto water Cherenkov detector (800 tons) that also serves as a shield against external neutrons and gamma rays. XMASS is a unique single phase liquid xenon detector that distinguishes itself by achieving the highest scintillation light yield among all current liquid xenon Dark Matter detectors, which allowed us to publish many competitive results.
XMASS data taking started with the commissioning phase which lasted from December 2010 through May 2012. After refurbishing the detector data taking resumed with significantly reduced background in November of 2013 and is currently scheduled to end towards the end of 2018. (Last update: 2018/05/17)