Design And Realization Of Electronics And Data Acquisition System For The PandaX Experiment

The first evidence for dark matter came in 1933 when Zwicky measured masses of Nebulae. The early 1970s, Vera Rubin used imaging spectrograph which was used to measure the electromagnetic spectrum to observe the Andromeda Nebula (M31) and calculated its rotation curve. Observation from Andromeda nebula found that most of the stars around the center of galaxies rotated with the same velocity. The most possible explanation of this phenomenon is present lot of quality but invisi-ble dark matter in spiral galaxies. Studies of gravitational lensing of galaxy clusters and cosmic microwave background affirm the existence of dark matter in astrono-my. Astrophysicist analysis data from Planck satellite to calculate structure of the universe with the ACDM model. The universe consists of about 4.9% baryons which constitute the ordinary matter, about 26.8% non-baryonic dark matter, and about 68.3% dark energy.As the existence of dark matter be confirmed by astrophysicist, theoretical physi-cists propose several dark matter candidates:hot dark matter, cold dark matter and warm dark matter. Hot dark matter mode can explain large-scale structure of uni-verse, but the cold dark matter can explain structure of galaxies, clusters of galaxies. Warm dark matter theory who is recently formated has characteristics of hot dark matter and cold dark matter.According to ACDM mode,83% of the matter in the universe is in a form of non-luminous, cold, collisionless, non-baryonic dark matter with low cross-section. Several theories which aim at solving the hierarchy problem predict stable weakly interacting massive particles (WIMPs) that could compose most of the dark matter. Their interactions with normal matter are on the order of a weak scale cross section. These theories predict the cross-section of WIMPs with particles of the Standard Model.From end of the 20th, particle physicists have been actively look for dark matter with experimental methods. In addition to the evidence from astronomical indirect observations which verify the existence of dark matter, particle physicists search for WIMPs particles in three ways:the underground low background direct dark matter experiments, indirect dark matter experiments, large accelerator. Direct dark matter experiments are designed to collect nuclear recoils signals from scattering of WIMPs with nucleus. Indirect dark matter experiments look for signatures of WIMPs anni-hilating to normal particles.The cryogenic crystal detector and cryogenic noble gas detectors are representa-tives of direct dark matter experiments. The representatives of indirect dark matter experiments are satellite experiments. LHC(Large Hadron Collider) is a representa-tive of large accelerator.In 2013, LUX (The Large Underground Xenon Experiment) obtained very high sensitivity result in dark matter detection. They reported results of the WIMP search data of 85.3 live days of data with a fiducial volume of 118 kg and haven’t found WIMP signals. They gave 90% confidence limits to be set on spin-independent WIMP- nucleon elastic scattering with a minimum upper limit on the cross section of 7.6× 10-46 cm2 at WIMP mass of 33GeV/c2.In 2013, AMS-02 (Alpha Magnetic Spectrometer) has measured the positron fraction (ratio of the positron flux to the combined flux of positrons and electrons). They have observed that from 0.5 to 10 GeV, the fraction decreases with increasing energy. The fraction then increases steadily between 10 GeV to 250 GeV. Yet the slope (rate of growth) of the positron fraction decreases by an order of magnitude from 20 to 250 GeV. At energies above 250 GeV, the spectrum appears to flatten but to study the behavior above 250 GeV requires more statistics.In 2014, Super-CDMS (Super Cryogenic Dark Matter Search) detected 11 sus-pected events of WIMPs with indirect dark matter detect mode. Data of 577 kg-days was analyzed for WIMPs with mass 5,7,10 and 15 GeV/c2 and detected 11 suspected events of WIMPs with 95% confidence. They gave 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 1.2×10-42cm2 at WIMP mass of 8GeV/c2. Suspected events have been negated by the results of LUX.Liquid noble gas detectors are currently the most talked about direct detection technology. The liquid xenon is a typical suitable material for direct WIMP detection. Xenon has a very good characteristics as the direct detection material:allows detector target masses to reach ton-scale within reasonable cost, allows discrimination between nuclear and electron recoils and allows self-shielding from external gamma rays.Given the breakthrough of XENON100 and LUX in the direct dark matter detec-tion, PandaX (The Particle and Astrophysical Xenon collaboration) designed first low background duel-phase xenon TPC of China in 2010. Target volume of PandaX increases from initially 120 kg (stage Ⅰ) to 0.5 t (stageⅡ) and eventually to a multi-ton scale. Most sub-systems and the stage Ⅰ TPC were transported to the China Jinping Deep-Underground Laboratory (CJPL) in August 2012. After successful installation, two engineering runs were carried out in 2013. The system has been collecting sci-ence data since late March 2014 and published results in 2014.9. PandaX reported results of the WIMP search data of 17.4 live days of data with a fiducial volume of 37 kg and haven’t found WIMP signals. We gave 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 3.7 x 10-44cm2 at WIMP mass of 49GeV/c2.PandaX dark matter detector is the lowest background detector in the world. As signals transfer and data acquisition part of PandaX, Electronic and Data acquisition system (EnDAQ) has to be designed and tested before physical run. System was designed with commercial module after 2010 in high energy physics group of Shandong university. After finishing software and trigger logic design, system collect photo-electron signals from PMT array. Then, system sets trigger threshold according to feature of recoil signals. EnDAQ starts initialization and setting of hardware. After start data acquisition, software holds data ready signal. When data is ready, system start verify event, build event, readout event and save data into disk array.The physical goal of EnDAQ is to achieve higher trigger efficiency on low en-ergy signals. In order to achieve this goal, we designed two version of trigger logic. 1st version was used in test run of PandaX to test detector function. Due to high trigger threshold of 1st version, system was upgraded for physical run.2nd version has significantly reduced the trigger threshold and significantly improve the trigger efficiency.In this paper a detailed description of design, installation and test of EnDAQ is presented.