Study On Simulation Of LHAASO-KM2A And Physical Expectation Of LHAASO

The basic study of cosmic rays(CRs)focus on its origin,acceleration sites and propagation since the CRs were discovered more than a century ago.High energy ?-rays,carrying the information of primary sources,are thus more powerful to probe the sources of CRs.With rapid development of the detection technology,the satellite-borne instrument discovered more than 3000 sources in GeV energies.In TeV energies,more than 200 gamma-ray sources have been firmly detected by the ground-based detectors,which is the new stage of gamma-ray astronomy.The high energy gamma-ray can be generated either by leptonic acceleration or by the hadronic acceleration.But there is no clear observation results above tens of TeV due to the limit of sensitivity of the current experiments,thus it is not enough to certify cosmic ray sources.However,the leptonic acceleration will not produce very high energy gamma-rays because of the Klein-Nishina effect,while the hadronic acceleration can produce gamma-rays above 100 TeV.It is thus expected that gamma-ray emission from tens of TeV to PeV will strongly help us to offer a judgement between different acceleration mechanisms,and then make a effective discriminant to search cosmic ray sources.Large High Altitude Air Shower Observatory(LHAASO),a next-generation ex-periment,will be built at 4410m above sea level near the Daocheng village,in Sichuan province,China.LHAASO is a hybrid EAS array,which contains KM2A array,WC-DA array and WFCTA array.KM2A,with an effective area of 1 km2,is the main part of LHAASO and dedicated to the observation of gamma-ray sources from 10 TeV to 20 PeV.In this thesis,we optimize the performance of KM2A and achieve the energy reso-lution of 23%,background rejection of 10-4,and the sensitivity of 1%of Crab above 50 TeV.Therefore,LHAASO is the most sensitive detector array at high energy region in the world.The most important major scientific goals of LHAASO is to measure the spectrum accurately from 300 GeV to 20 PeV and to explore the origin of high energy CRs.In this thesis,we will investigate,basing on the different acceleration models,the ability of LHAASO on the measurement of spectra of Supernova remnants,supperbubble,diffuse galactic ?-rays and Active Galactic Nuclei flares.This expectation,especially at energies above 30 TeV,will be sufficiently offer a final judgment between different acceleration mechanisms in the ultra high energy region,and will be the foundation to study the origin of CRs.Based on the Geant4,the full simulation of KM2A has been designed and developed to accurately describe the geometry of detectors as well as the response of extensive air shower particles in these detectors.But the full simulation consumes a lot of CPU time when producing large volume of data samples.Therefore,we propose and develop a sim-plified method of KM2A simulation,which produces the consistent results with the full simulation.It will be the necessary preparations to produce quantities of simulation data for LHAASO,and then help us to comprehend the experiment data.Besides that,the suc-cessful operation of simplified simulation method in the LHAASO software framework will lay a solid foundation for analysis of experimental data between the three sub-arrays in the LHAASO.