Low-level Data Processing And Beam Systematic Study For The AliCPT Experiment

In recent decades,studies and measurements of the Cosmic Microwave Back-ground have promoted the development of Cosmology.Especially,observing the temperature anisotropies of the CMB has provided many evidences that there is a inflation epoch in the early Universe.The Inflation theory was first proposed by Alan Guth and Andrei Linde in 1981.by making an assumption that shortly after the Big Bang,the Universe will into a period of faster-than-light expansion.The quantum vacuum fluctuations during the inflation period will imprint the Universe real density distribution.The density distribution evolved during the Universe expansion and formed all the structure in the Universe today.The In-flation theory also predicted that the gravitational wave will be produced during inflation period.The existence of gravitational wave will lead to a special mode of CMB polarization,the so-called B-mode polarization.In data analysis pipeline,we use BB power spectrum to quantitative describe the anisotropy of B-mode polarization.Detecting inflationary B-mode would give us a strong,direct ev-idence for the existence of inflation.Thus there are many experiments devote themselves to detect the inflation B-mode polarization.Measurements of the CMB polarization are very sensitive to systematic con-tamination,because the temperature anisotropies signal is at the level of 10-4K.and the polarization is even much smaller than the temperature,only 10%of the temperature,so even a tiny systematic error will cause spurious B-mode signal,and impact the detection of inflation B-rnode.There are two ways to mitigate such spurious signal.The first is to add some new modules or change the archi-tecture of the instruments.The second is to mitigate the spurious polarization signal during data analysis procedure.The work of this thesis is a part of data analysis pipeline of Ali CMB Polariza-tion Telescope(AliCPT).to make sure that the algorithm can remove the spurious polarization signals as much as possible and minimize the effects in the following data processing procedures.In this thesis,a so-called deprojection method,which is an self-calibration way to mitigate the systematic from beam mismatch during data analysis was used.We studied the influence of beam mismatch systematic on the BB power spectrum by simulating all the data product.We verify the validity by comparing the B-mode power spectra before and after deprojection.The thesis consists of the following sections:brief introduction of cosmology,ob-serving method,systematic error simulation,data analysis,systematic mitigation and deprojection results.