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The tiny modification of dispersion relation induced by Lorentz violation (LV) is an essential issue in quantum gravity (QG) theories, which can be magnified into significant effects when dealing with astrophysical observations at high energy and long propagation distance. LV would lead to photon decay at high energies, therefore, observations of high-energy photons could constrain LV or even QG theories. The Large High Altitude Air Shower Observatory (LHAASO) is the most sensitive gamma-array instrument currently operating above 100 TeV. Recently, LHAASO reported the detection of 12 sources above 100 TeV with maximum photon energy exceeding 1 PeV. According to these observations, the most stringent restriction is achieved in this paper, i.e., limiting the LV energy scale to $1.7\times10^{33} $ eV, which is over 139,000 times that of the Planck energy and achieve an improvement of about 1.9 orders of magnitude over previous limits., AMS-LaTeX 2.0, 7 pages, 3 figures

In the Large High Altitude Air Shower Observatory project, Muon detectors will be built at 4400m above sea level. As water cerenkov detector, 44 tons of ultrapure water should be infused into the Muon detector. In this cold area, once the water inside the Muon detector freezes, consequence would be very serious. In this paper, a simulation of water temperature is built, the simulation data are consistent with the temperature data of Muon detector at yangbajing Tibet. Using the same simulation with air temperature, soil moisture and temperature of Dao cheng, an antifreeze solution was designed. Through two years of testing, the design is successful.

The Large High Altitude Air Shower Observatory (LHAASO), to be built at 4410 m a.s.l. near the Daocheng in the Sichuan province of China, is a new generation EAS array. It consists of three kinds of detector arrays. KM2A is the main array of LHAASO and is composed of 5195 electromagnetic particle detectors and 1171 muon detectors, which are distributed in an area of 1.3 km2. In this work, we study the trigger logics of KM2A, which will adopt an unprecedented software trigger system. Taking into account the characters of real cosmic ray events, we investigate the trigger logics by adjusting the space window and time window together. In this study, we adopt the CORSIKA to simulate the shower development and a parameterization code to simulate the detector response. We also develop a toy simulation to estimate the noise event rate due to chance coincidence noise hits. With the principle to maximize the real cosmic ray events in the same time to inhibit the noise events, we achieve an optimized trigger criterion for KM2A. The corresponding threshold energy for gamma-ray is about 4 TeV, which is much lower than the previous initial trigger logic. The performances of KM2A with this trigger criterion are also presented.

'G4argo', a GEANT4-based simulation package for the ARGO-YBJ detector, is described in this paper. G4argo incorporates in the simulation the true RPC time resolution and another 0.5 ns time uncertainty which is introduced from the offline calibration of TDC. In addition, the correct RPC geometry and the true materials for the ARGO-YBJ experimental hall are implemented. As a result, G4argo simulation shows a very good agreement with real data.

We present here the results of observation of very high energy(VHE) gamma-ray emission from Crab Pulsar with Beijing; Atmospheric Cerenkov Telescopes,. named ACT2 and ACT3, for the duration of the fall 1995-spring 1996 season. The data are based on 168 hours (ACT2) and 125 hours (ACT3) of exposure over the period of observation in tracking model. After conversion the event time to the solar barycenter, the data have been searched for evidence of pulsed emission at 33ms period of Crab Pulsar. We found no steady emission of VHE Gamma-ray with 33ms period at the scale of month or night. But there are two evidences of sporadic emission over an hour duration with the same period as the one at radio frequency.

Cosmic rays can interact with the solar atmosphere and produce a slew of secondary messengers, making the Sun a bright gamma-ray source in the sky. Detailed observations with Fermi-LAT have shown that these interactions must be strongly affected by solar magnetic fields in order to produce the wide range of observational features, such as high flux and hard spectrum. However, the detailed mechanisms behind these features are still a mystery. In this work, we tackle this problem by performing particle-interaction simulations in the solar atmosphere in the presence of coronal magnetic fields modeled using the potential field source surface (PFSS) model. We find that the low-energy (~GeV) gamma-ray production is significantly enhanced by the coronal magnetic fields, but the enhancement decreases rapidly with energy. The enhancement is directly correlated with the production of gamma rays with large deviation angles relative to the input cosmic-ray direction. We conclude that coronal magnetic fields are essential for correctly modeling solar disk gamma rays below 10GeV, but above that the effect of coronal magnetic fields diminishes. Other magnetic field structures are needed to explain the high-energy disk emission.