| Substantial evidence from astrophysical and cosmological observations support the existence of dark matter(DM),and show that DM is a major part of the composition of the universe.Weakly Interacting Massive Particles(WIMPs)are considered to be one of the most likely candidates of DM particle.The direct search for WIMPs has be-come a frontier topic in physics today.In recent decades,various underground detection experiments(such as XENON,LUX)have launched direct search for WIMPs.The PandaX experiment,located in the China Jinping Underground Laboratory(CJPL),employs the advanced dual phase xenon time projection chamber to directly detect WIMPs,and observes the luminescence and ionization signals generated by the rare DM interaction in liquid xenon,and further reconstructs the location and energy of the events.PandaX collaboration consists of members from more than ten universities and institutes including Shanghai Jiaotong University and Shanghai Institute of Applied Physics.The first phase of the experiment,PandaX-I,was completed in 2016,with an exposure of 54.0 kg×80.1 day to obtain the leading DM search results in the world at that time.The second phase of the experiment,PandaX-?,with a half-ton scale liquid xenon target,started to performe a extensive WIMP search in 2016,and officially ended in June 2019,accumulating a total exposure of 132 ton·day.PandaX-? reported the most stringent limit on the spin-independent(SI)elastic WIMP-nucleon scattering cross section with a total exposure of 33 ton·day in 2016 and 54 ton·day in 2017,and the minimum excluded cross section was set to be 2.5×10-46and 8.6×10-47cm2for the WIMP mass of 40 GeV/(82,respectively.In this dissertation,I will focus on the PandaX-? experiment and the data anal-ysis for the full 132 ton·day exposure.For the data analysis,some key topics in the analysis process and the improvement of various analysis techniques will be mainly discussed,including the data processing in PandaX-?,data quality cuts,detector re-sponse and correction,position reconstruction and energy reconstruction,calibration of low energy nuclear recoil and electron recoil events and the corresponding signal model,backgrounds estimation,selection and discussion on final candidates in DM search data,and the final sensitivity and exclusion limit by the profile likelihood fitting method.In the analysis on the full exposure data of PandaX-?,no significant excess is found above the background,leading to an uppper limit of the SI elastic WIMP-nucleon cross section with a lowest excluded value of 2.2×10-46cm2at a WIMP mass of 30 GeV/(82.With the above research,we develop experimental and analysis techniques for liquid xenon detectors,and acquire crucial experiences for the next generation of PandaX program,i.e.,PandaX-4T,to explore more parameter space of WIMPs in the future. |
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