Nuclei composition discrimination study based on Cherenkov image of air shower

Purpose In ground-based cosmic ray experiments,the Cherenkov image detected by imaging air Cherenkov telescopes contains crucial information about the longitudinal development of Extensive Air Showers,which can be used for composition discrimination between different nuclei.Methods Proton and iron showers were simulated to study the composition discrimination in the energy range from~100TeV to~10PeV with a zenith angle of 45°.A new variable,namelyθ_(x)^(max),was introduced from the longitudinal development of Cherenkov photons,which represents the posi tion at which the angular ditribution of Cherenkov photons detected by telescope reached maximum.Results Comparing to the shower maximum of Cherenkov photons(X_(Cer)^(max)),it was found that below|PeV,θ_(x)^(max)has better composition discrimination ability compared to X_(Cer)^(max)xar,while they have similar composition discrimination ability above PeV.Conclusions For nuclei composition identification,omax performed better than Xax,especially in low energies(below the PeV range).This is due to thatθ_(x)^(max)is suffering less statistical fuctuations compared to XX_(Cer)^(max)Meanwhile,θ_(x)^(max)is less afected by the statistics of Cherenkov photons compared to X_(Cer)^(max)

Simulation of silicon strip detector for space-based cosmic ray experiments with Allpix^(2)

Purpose Silicon strip detectors are widely applied in space-based cosmic ray experiments and most of the silicon strip detectors deploy an analytical method for its digitization.However,the analytical method simplifies the physical process of propagation of electrons/holes generated inside the silicon detector by particles that pass through the detector.In order to simulate silicon strip detectors with different configurations comprehensively,the Allpix^(2),an open-source software,is used to study those processes.Methods When particle passes through the silicon detector,energy is deposited based on Geant4 simulation,and electron-hole pairs are created due to the deposited energy.The Allpix^(2)simulation method and the analytical method are both used to calculate or simulate the diffusion and drift processes that electron-hole pairs propagate inside the silicon detector under internal electric field,and the number of electrons/holes accumulated at implanted strips are counted.Results and conclusion The number of electrons/holes accumulated along the implanted strips are compared between the Allpix^(2)simulation method and analytical method for different incident angles and different incident positions,they are found to be in good agreement for proton particles,while there are discrepancies for carbon and silicon particles.The Allpix^(2)software may be an important tool for the study of response of silicon strip detectors in space.The charge resolution of single implanted strip predicted by Allpix^(2)simulation method is about 4.7%for proton,3.8%for carbon and 1.6%for silicon particles for an incident angle of 45◦.

Extinction coefficients of surface atmospheric aerosol above LHAASO

We investigate the extinction coefficients of the surface atmospheric aerosol over the Large High Altitude Air Shower Observatory (LHAASO), located at the Haizi Mountain, Daocheng County, China. To this end, we utilize the Longtin model, Mie scattering theory, and experimental data obtained by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Our theoretical calculations show that the total extinction coefficients of the atmospheric aerosol at the wavelength of 200–500 nm are inversely proportional to the laser wavelength, and influenced by the wind speed. From July 2015 to October 2016, the extinction coefficient of the surface atmospheric aerosols at 532 nm wavelength reached 0.04 km^-1 with no wind, while it increased to 0.1 km^-1 with gusts. In this period, the extinction coefficients of the surface atmospheric aerosol at 532 nm wavelength, obtained by the CALIPSO, change from 0.01 to 0.07 km^-1, which is less than the values obtained the theoretical calculation and larger than the average of Tibetan Plateau in 2006-2016. These calculations and experimental evidence provide important arguments to the model of atmospheric aerosol to be applied in the calibration of LHAASO. Our results suggest that the extinction coefficients over LHAASO require further study, including research on the size distribution, shape, concentration of aerosols particles, wind dependence, relative humidity dependence, etc.