Study On The Gaseous Prototype Detector For ¹³⁶Xe Nuclear Neutrinoless Double Beta Decay

The experiments on neutrino oscillation in the recent 20 years have demonstrated that neutrino has non-zero mass.However,it still remains a mystery whether the neutrino mass term is Dirac or Majorana.The most straightforward way to solve the problem is the detection of the neutrinoless double beta decay?NLDBD?,which is equivalent to the Majorana neutrino.And it can further lead to lepton number violation,which is the new physics beyond the standard model.In this thesis key topics of PandaX-? project on detecting ¹³⁶Xe NLDBD is discussed.The project is based on the technology of Time Projection Chamber?TPC?in particle physics experiment,where 200 kg of high pressure xenon will be contained inside.Secondary electrons ionized by the electrons from ¹³⁶Xe nucleus decay in TPC drift towards the readout plane with the electric field and are thus collected.Accordingly,the energies of the initial electrons can be recorded.Micromegas is chosen as the readout plane of our detector.Tracks in the gaseous xenon will be used to identify different even types,which suppresses the background and improves the detector sensitivity.To demonstrate the key technology of the PandaX-? detector and calibrate some of its features,we built a scaled-down prototype detector which can contain 20 kg of high pressure xenon,then it was tested and run for a year.In 5 bar xenon,the prototype achieved an energy resolution of 14.1%for the59.5 keV peak in the ²⁴¹Am calibration spectrum,corresponding to an energy resolution of 2.19%for 2458 keV,which is the NLDBD Q value.Moreover,we highlighted the tracking ability of the detector.This thesis includes topics of the PandaX-? 200 kg detector and its sensitivity analysis,the corresponding technologies of detector,and the design and commissioning of the detector prototype.The detailed description of each chapter is given below:In Chapter 1 the physics about neutrino is discussed,from the neutrino oscillation to the mystery of neutrino mass,finally leading to the NLDBD experiment.In Chapter 2 the PandaX-? Project on NLDBD detection is introduced and the corresponding NLDBD experiment technologies are discussed.In Chapter 3 the sensitivity of the project is discussed and calculated based on the parameters given in Chapter 2.For demonstration and calibration of the experiment we built a prototype detector.In Chapter 4 to 7 the work of the prototype detector is shown.Chapter 4 shows the set up of the detector in detail,including the high pressure vessel,the TPC,the electronics and data aquisition system,and the gas system.Chapter 5 and 6 introduce Micromegas in detail,which is one of the key features of PandaX-? project,including its structure,fabrication and test.In Chapter 7 the commissioning and data of the prototype detector are shown.In Chapter 8 the work of this thesis is concluded and plans and prospections of the project are shown.