Study Of The Cosmic-ray Fractionally Charged Particle With DAMPE Experiment

In 1909,the oils’ drop experiment was performed by Millikan,it was the first direct measurement of electron charge,which was also the first time that humans measured the charge of elementary particles.Since then,particles detected have been observed to carry charges that are integer multiples of e.The QCD theory indicated that free quarks do not exist,research interest in fractionally charged particles(FCP)was driven by the search for free quarks.Further,the Standard Model(SM)was established to classify the elementary particles but did not have free FCP.Nevertheless,there are still theories and experiments dedicated to finding free quarks,either to extend the SM theory or to discover new particles but these have not yielded confirmatory results.The goal of searching for free quarks has been extended to a wider search for free FCP,including composite FCP and milli-charge particles,by the extension of SM or not relying on any theory.The search for FCP was mainly carried out in two directions:search for FCP on accelerator devices and search for FCP existing in nature.The DArk Matter Particle Explorer(DAMPE)is the first scientific satellite launched by China to study the high-energy cosmic rays and gamma rays in space.One of the scientific objectives of DAMPE is to search for dark matter in an indirect approach that involves examining high-energy cosmic rays in space.DAMPE has been working stably on orbit for more than 7 years and accumulating amounts of scientific datasets.To deepen the potential of DAMPE,based on the relatively large acceptance and the characteristics of long-term continuous observation on orbit,an extended goal of searching for FCP is proposed.The author has studied the working status of the key sub-detector BGO calorimeter and studied the FCP in cosmic rays based on utilizing five-year on-orbit data of the DAMPE detector.The on-orbit working status of the BGO calorimeter.This work,completed by the author independently,is both the extension of the original scientific goals of DAMPE and the exploration of new physics beyond the SM theory with DAMPE.The working status of the BGO calorimeter is monitored through the stability of the calibration parameters,including the pedestal,the linearity of the dynode ratio of PMT,and the energy scale of MIPs,among which the energy scale stably fluctuate within 1%.The calibration process assures the reliability of energy reconstruction of the BGO calorimeter.The radiation aging effect of the BGO cell at the different parts of the space radiation environment is analyzed through the variation of the quenching factor and the attenuation length.The stable performance is not affected by the space radiation and is demonstrated by checking the energy linearity between the energy deposition in the shower maximum and total energy deposition.The search for heavy lepton-like FCP based on five-year on-orbit data of DAMPE is introduced.1.The behavior and main background sources of FCP in the DAMPE detector are analyzed.The MC simulation of the FCP signal is produced by creating a virtual FCP particle in DAMPE software based on the Geant4 toolkit.A series of selection criteria are set to screen the data samples out.The charge spectra of plastic scintilliator detector(PSD)and silicon-tungsten tracker converter(STK)are obtained,and the signal region of FCP is determined by the charge distributions of FCP MC.2.Applying the signal region to the on-orbit data,no FCP signal is observed.The efficiencies of selections and the main sources of systematic error are evaluated.Finally,the 90%confidence level(C.L.)flux upper limit of FCP in cosmic rays is determined as Φ<6.2 × 10-10 cm-2sr-1s-1.The accuracy is three orders of magnitude higher than other same-type experiments.The further exploration of light-mass FCP based on the on-orbit data of DAMPE is envisaged.The feasibility of studying the light-mass FCP is determined by analyzing one-year on-orbit data.The goal of measuring the differential flux spectrum or flux upper limit spectrum related to the energy of light-mass FCP is proposed.A preliminary plan is also formulated for future work.