University of Michigan
Who participated in PandaX in 2011?
PandaX The Particle and Astrophysical Xenon Detector , or PandaX , is a dark matter detection experiment at China Jinping Underground Laboratory ( CJPL ) in Sichuan , China . The experiment occupies the deepest underground laboratory in the world , and is among the largest of its kind . Participants . The experiment is run by an international team of about 40 scientists , led by researchers at Chinas Shanghai Jiao Tong University . The project began in 2009 with researchers from Shanghai Jiao Tong University , Shandong University , the Shanghai Institute of Applied Physics , and the Chinese Academy of Sciences . Researchers from the University of Maryland , Peking University , and the University of Michigan joined two years later . The PandaX team also includes members from the Ertan Hydropower Development Company . 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 . The use of both liquid and gaseous phases of xenon , similarly to the XENON and LUX experiments , allows the location of events to be determined , and gamma ray events to be vetoed . In addition to searching for dark matter events , PandaX is designed to detect Xe-136 neutrinoless double beta decay . Laboratory . PandaX is located at China Jinping Underground Laboratory ( CJPL ) , the deepest underground laboratory in the world at more than below ground . The depth of the laboratory means the experiment is better shielded from cosmic ray interference than similar detectors , allowing the instrument to be scaled up more easily . The muon flux at CJPL is 66 events per square meter per year , compared with 950 events/m/year at the Sanford Underground Research Facility , home of the LUX experiment , and 8,030 events/m/year at the Gran Sasso lab in Italy , home to the XENON detector . The marble at Jinping is also less radioactive than the rock at Homestake and Gran Sasso , further reducing the frequency of false detections . Wolfgang Lorenzon , a collaborating researcher from the University of Michigan , has commented that the big advantage is that PandaX is much cheaper and doesnt need as much shielding material as similar detectors . Operational stages . Like most low-background physics , the experiment is constructing multiple generations of detectors , each serving as a prototype for the next . A larger size allows greater sensitivity , but this is only useful if unwanted background events can be kept from swamping the desired ones ; ever more stringent limits on radioactive contamination are also required . Lessons learned in earlier generations are used to construct later ones . The first generation , PandaX-I , operated until late November , 2014 . It used of xenon ( of which served as a fiducial mass ) to probe the low-mass regime ( <10 GeV ) and verify dark matter signals reported by other detector experiments . PandaX-I was the first dark matter experiment in China to use more than 100 kg of xenon in its detector , and its size was second only to the LUX experiment in the United States . PandaX-II , completed in March 2015 and currently operational , uses of xenon ( approximately 300 kg fiducual ) to probe the 10–1,000 GeV regime . The PandaX-II reuses the shield , outer vessel , cryogenics , purification hardware , and general infrastructure from the first version , but uses a much larger time projection chamber , inner vessel of higher purity ( much less radioactive Co ) stainless steel , and cryostat The construction cost of PandaX is estimated at US$15 million , with an initial cost of $8 million for the first stage . PandaX-II produced some preliminary physics results from a brief commissioning run in late 2015 ( November 21 to December 14 ) before the main physics run currently underway through 2018 . PandaX-II is significantly more sensitive than both the 100-kg XENON100 and 250-kg LUX detectors . XENON100 , in Italy has , in the three to four years prior to 2014 , produced the highest sensitivities over a wide range of WIMP masses , but was leapfrogged by PandaX-II . The most recent results on the spin-independent WIMP-nucleon scattering cross-section of PandaX-II were published in 2017 . 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 , Im excited about seeing China developing a fundamental physics program .