PandaX

The experiment is run by an international team of about 40 scientists, led by researchers at China's Shanghai Jiao Tong University. The project began in 2009 with researchers from Shanghai Jiao Tong University, Shandong University, the Shanghai Institute of Applied Physics (zh), and the Chinese Academy of Sciences. Researchers from the University of Maryland, Peking University, and the University of Michigan joined two years later. Scientists from University of Science and Technology of China, China Institute of Atomic Energy and Sun Yat-Sen University joined PandaX in 2015. ==Design and construction==

PandaX is a direct-detection experiment, consisting of a dual-phase xenon time projection chamber (TPC) detector. It used of xenon (of which served as a fiducial mass) to probe the low-mass regime (60Co) stainless steel, and a cryostat. The construction cost of PandaX is estimated at US$15 million, with an initial cost of $8 million for the first stage. (±1σ sensitivity band in green). PandaX-II is significantly more sensitive than both the 100-kg XENON100 and 250-kg LUX detectors. In September 2018 the XENON1T experiment published its results from 278.8 days of collected data and set a new record limit for WIMP-nucleon spin-independent elastic interactions. The next stages of PandaX are called PandaX-xT. An intermediate stage with a four-ton target (PandaX-4T) is under construction in the second-phase CJPL-II laboratory. The ultimate goal is to build a third generation dark matter detector, which will contain thirty tons of xenon in the sensitive region. ==Initial results==

The majority of the PandaX experimental equipment was transported from Shanghai Jiao Tong University to China Jinping Underground Laboratory in August 2012, and two engineering test runs were conducted in 2013. The initial data-collection run (PandaX-I) began in May 2014. Results from this run were reported in September 2014 in the journal Science China Physics, Mechanics & Astronomy. In the initial run, about 4 million raw events were recorded, with around 10,000 in the expected energy region for WIMP dark matter. Of these, only 46 events were recorded in the quiet inner core of the xenon target. These events were consistent with background radiation, rather than dark matter. The lack of an observed dark-matter signal in the PandaX-I run places strong constraints on previously-reported dark matter signals from similar experiments. ==Reception==

Stefan Funk of the SLAC National Accelerator Laboratory has questioned the wisdom of having many separate direct-detection dark matter experiments in different countries, commenting that "spending all our money on different direct-detection experiments is not worth it." Xiangdong Ji, spokesperson for PandaX and a physicist at Shanghai Jiao Tong University, concedes that the international community is unlikely to support more than two multi-tonne detectors, but argues that having many groups working will lead to faster improvement in detection technology. Richard Gaitskell, a spokesperson for the LUX experiment and a physics professor at Brown University, commented, "I'm excited about seeing China developing a fundamental physics program." ==References==