Mingjun Chen

Knee of the cosmic hydrogen and helium spectrum below 1 PeV measured by ARGO-YBJ and a Cherenkov telescope of LHAASO

The measurement of cosmic ray energy spectra, in particular for individual species, is an essential approach in finding their origin. Locating the knees of the spectra is an important part of the approach and has yet to be achieved. Here we report a measurement of the mixed Hydrogen and Helium spectrum using the combination of the ARGO-YBJ experiment and of a prototype Cherenkov telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a clear steepening of the spectrum, is observed. This gives fundamental inputs to galactic cosmic ray acceleration models.

Properties and performance of two wide field of view Cherenkov/fluorescence telescope array prototypes

A wide field of view Cherenkov/fluorescence telescope array is one of the main components of the Large High Altitude Air Shower Observatory project. To serve as Cherenkov and fluorescence detectors, a flexible and mobile design is adopted for easy reconfiguring of the telescope array. Two prototype telescopes have been constructed and successfully run at the site of the ARGO-YBJ experiment in Tibet. The features and performance of the telescopes are presented

Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.

The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called knee by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber (RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range (100–700 TeV). The observed energy spectrum is compatible with a single power law with index γ=−2.63±0.06.

A method to monitor and measure the water transparency in LHAASO-WCDA using cosmic muon signals

The Large High Altitude Air Shower Observatory (LHAASO) is to be built at Daocheng, Sichuan Province, China. As one of the major components of the LHAASO project, a Water Cherenkov Detector Array (WCDA), with an area of 78,000~

Study on the optimization of the water Cherenkov detector array of the LHAASO project for surveying VHE gamma ray sources

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The time calibration system for the LHAASO-WCDA experiment

, contains 350,000~tons of purified water. The water transparency and its stability are critical for successful long-term operation of this project. To gain full knowledge of the water Cherenkov technique and investigate the engineering issues, a 9-cell detector array has been built at the Yangbajing site, Tibet, China. With the help of the distribution of single cosmic muon signals, the monitoring and measurement of water transparency are studied. The results show that a precision of several percent can be obtained for the attenuation length measurement, which satisfies the requirements of the experiment. In the near future, this method could be applied to the LHAASO-WCDA project.

The dynamic range extension system for the LHAASO-WCDA experiment

It is prpopsed that a water Cherenkov detector array, LHAASO-WCDA, is to be built at Shangri-la, Yunnan Province, China. As one of the major components of the LHAASO project, the main purpose of it is to survey the northern sky for gamma ray sources in the energy range of 100 GeV-30 TeV. In order to design the water Cherenkov array efficiently to economize the budget, a Monte Carlo simulation is carried out. With the help of the simulation, the cost performance of different configurations of the array are obtained and compared with each other, serving as a guide for the more detailed design of the experiment in the next step.

A new method of The Monte Carlo Simulation based on Hit stream for the LHAASO

The Water Cherenkov Detector Array (WCDA), which is one of the main components of the Large High Altitude Air Shower Observatory n(LHAASO), functions as surveying the northern sky for high-energy gamma ray sources at the energy range around 100 GeV–30 TeV. The precision of the time measurement for shower particles hitting every detector in the array directly associates the detection sensitivity for the sources. In order to make the pointing error of the detector to any point source less than 0.1 ◦ , the calibration precision of the time offsets among detector cells should be less than 0.2 ns. To reach this goal, a method called “cross calibration” is to be employed for the detector array, with 180 bundles of fiber systems guiding the lights of LEDs to each PMT. A prototype of the time calibration system is developed, which is based on a fast LED, a plastic fiber bundle and an FPGA control board. The prototype is tested in the lab and the error propagation based on the measured parameters shows that it fulfills the requirement.

Study on single-channel signals of water Cherenkov detector array for the LHAASO project

The Large High Altitude Air Shower Observatory (LHAASO) will be constructed at Mountain Haizi, in Sichuan Province, China (4410m a.s.l.). The Water Cherenkov Detector Array (WCDA), one of the major component of the LHAASO, will focus on surveying the northern sky for gamma ray sources from 100 GeV to 30 TeV. The whole WCDA, owing an area of 78,000 m^{2}, is subdividing into 3120 detector cells (5×5 m^{2} each, with a water depth of 4m). Every cell has an 8 or 9-in PMT residing at the bottom to collect Cherenkov lights produced by the charged secondary particles of air showers. To observe high-energy shower events, especially to measure precisely the shower cores of events at the energy range from 100 TeV to 10 PeV for an analysis of the cosmic ray spectrum, as a dynamic range extension system, another sets of small PMTs (1-2 inch) will be added to 900 cells of the WCDA array. In this talk, the design and status of this dynamic range extension system is presented.

Test bench for fibers of the LHAASO-WCDA time calibration system

The Large High Altitude Air Shower Observatory (LHAASO) nwill be constructed at Mt. Haizi in Sichuan Province, China. Among nseveral detector components of the LHAASO, the Water Cherenkov nDetector Array (WCDA) is of great importance for low-to-middle nenergy gamma ray physics. The WCDA has an area of 78,000