A prototype array for the LHAASO-KM2A, which consists of 42 detector units and fully overlaps the ARGO-YBJ experiment, was set up at the Yangbajing cosmic ray observatory and has been in stable operation since Octoter 2010. The resulting performances of the KM2A electromagnetic particle detector prototypes fully meet the design requirements. Through hybrid observation of cosmic ray showers with the ARGO-YBJ experiment, the performances and long-term stability of the prototype array are tested and the results are consistent with expectation. The cosmic ray moon shadow observed by the prototype array is also presented.
In the Large High Altitude Air Shower Observatory（LHAASO） project,the one kilometer square extensive air shower array（KM2A） is the the largest detector array in terms of effect ive area.It consists of 5635electromagnetic particle detectors（EDs） and 122 1 union detectors（MDs）.Each ED is composed of 16 scintillator tiles readout by wavelength-shifting fibers that are bundled and attached by a 25 mm PMT.The design of the unit and its performances,such as photoelectron yield,time resolution and uniformity,are discussed in detail.An assembling scheme for the whole ED is established to guarantee the uniformity throughout all 16 tiles in a single ED and all EDs in mass production.
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.
The knee phenomenon of the cosmic ray spectrum, which plays an important role in studying the acceleration mechanism of cosmic rays, is still an unsolved mystery. We try to reconcile the knee spectra measured by ARGO-YBJ and Tibet-III. A simple broken power-law model fails to explain the experimental data. Therefore a modified broken power-law model with non-linear acceleration effects is adopted, which can describe the sharp knee structure. This model predicts that heavy elements dominate at the knee.
Considering the octet baryons in relativistic mean field theory and selecting entropy per baryon S=1, we calculate and discuss the influence of U bosons on the equation of state, mass-radius, moment of inertia and gravitational redshift of massive protoneutron stars （PNSs）. The effective coupling constant gu of U bosons and nucleons is selected from 0 to 70 GeV-2. The results indicate that U bosons will stiffen the equation of state （EOS）. The influence of U bosons on the pressure is more obvious at low density than high density, while the influence of U bosons on the energy density is more obvious at high density than low density. The U bosons play a significant role in increasing the maximum mass and radius of PNS. When the value of gu changes from 0 to 70 GeV-2, the maximum mass of a massive PNS increases from 2.11M to 2.58Me, and the radius of a PNS corresponding to PSR J0348＋0432 increases from 13.71 km to 24.35 km. The U bosons will increase the moment of inertia and decrease the gravitational redshift of a PNS. For the PNS of the massive PSR J0348＋0432, the radius and moment of inertia vary directly with gu, and the gravitational redshift varies approximately inversely with gu.
