| The astronomical observations during almost one century have made dark matter very important in modern fundamental physics.Although there are countless observational evidences that support the existence of dark matter,they almost all come from gravitational effects.Scientists have proposed many theoretical models of dark matter,but we much lack of real knowledge of it.In order to search for dark matter,to answer what it is,particle physicists try to detect signals emitted by the collision between dark matter particles and ordinary particles in underground laboratories,find evidence of dark matter particle production on the accelarators,or search for products of dark matter particles’ annihilation in cosmic-rays.With the launch of DAMPE,which is a satellite-borne experiment for cosmic-ray observation,China joined in the indirect detection of dark matter.The first scientific object of DAMPE is to measure spectra of cosmic-rays and γ-rays where may lie the signals emitted by dark matter particles.In addition,DAMPE aims to study the cosmicray physics and y-ray astronomy.DAMPE was not originally intended to observe and measure cosmic-ray positrons due to the disability of measuring the sign of particle charge.This thesis is to exploit the geomagnetic effects in.the orbit data of DAMPE,and to measure separate spectra of cosmic-ray electrons and positrons with the help of them.The study is related to the search for dark matter.Besides,it has got extra objects of research for DAMPE.The check of energy measurement of calorimeters in high energy has always been difficult in orbit experiment,due to lack of sources of particles with precisely known energies.Based on the features of the geomagnetic field and the desciptive models of it,the thesis introduces the study on the response of the BGO calorimeter of DAMPE,taking advantage of the energy scale of geomagnetic cutoff in the cosmic-ray spectra.The thesis gives a detailed introduction to the method of simulating the interaction between on-orbit cosmic-rays and the geomagnetic field.The behavior of particles with energies around the cutoff and their energy deposition in the calorimeter were compared to the simulated results,to give a study on the calorimeter’s response.The study implied the uncertainty of energy measurement at up to 100 GeV,increasing the upper limit of previous methods by several times.The energy measurements of the geomagnetic cutoffs are in agreement with the computated results within the proper uncertainty of this comparison method.Making use of the above techniques and methods,cosmic-ray electrons and positrons were separately measured.The geomagnetic field bends electons/positrons in propagation to different sides,following the sign of charge.In the east,there are some directions from which only electrons can arrive at DAMPE,while in the west there are some directions only for positrons.Electrons and positrons were separately identified with these special incident directions enclosed by the two "horizons" of electrons and positrons separately,which were again determined by the numerical simulation mentioned above.The proton events in the separated data sample were excluded.Limited by the present observation mode and field of view of DAMPE,this separation can only be done when the particle energy is below～20 GeV.Thus the thesis focuses on the exploitaion of the research method,though also gives the spectra below～20 GeV and the corresponding "positron fraction".In face with the limitation of field of view,a simulation was performed to study the capability of positron measurement if DAMPE kept an inclination of 60° during its observation.The foreseen result of measured positron spectrum was compared to the published result of Fermi-LAT.It was indicated that the method discussed here could only be applied to positrons up to～200 GeV due to the limited strength of the geomagnetic field,and that after a 4-year observation,DAMPE would have got similar statistics to the Fermi-LAT measurement.The work in this thesis has as the first one used geomagnetic cutoff energy of cosmic-ray nuclei to study the response of on-orbit calorimeter.This method can reach higher energy scale than the other methods that currently exist and gives a new idea for checking the energy measurement of on-orbit apparatus.The separate observation of cosmic-ray electrons and positrons has extended the research methods and subjects of DAMPE.The study has given reference to the pointed observation of DAMPE or of other future space experiments that do not have magnets for the identification of cosmic-ray positrons. |
