Data from the Tibet III air shower array (with energies around 3 TeV) and from the Tibet II array (with energies around 10 TeV) have been searched for diffuse gamma rays from the Galactic plane. These arrays have an angular resolution of about 0=9. The sky regions searched are the inner Galaxy, 20 l 55 , and outer Galaxy, 140 l 225 , and jbj 2 or 5 . No significant Galactic-plane gamma-ray excess was observed. The 99% confidence level upper limits for gamma-ray intensity obtained are (for jbj 2 ) 1:1 Â 10 À15 cm À2 s À1 sr À1 MeV À1 at 3 TeV and 4:1 Â 10 À17 cm À2 s À1 sr À1 MeV À1 at 10 TeV for the inner Galaxy, and 3:6 Â 10 À16 cm À2 s À1 sr À1 MeV À1 at 3 TeV and 1:3 Â 10 À17 cm À2 s À1 sr À1 MeV À1 at 10 TeV for the outer Galaxy, assuming a differential spectral index of 2.4. The upper limits are significant in the multi-TeV region when compared to those from Cerenkov telescopes in the lower energy region and other air shower arrays in the higher energy region; however, the results are not sufficient to rule out the inverse Compton model with a source electron spectral index of 2.0.

for the LHAASO Collaboration † EN-detectors (Electron-Neutron Detector) can provide detection of both electrons and thermal neutrons generated in ground by secondary hadrons of extensive air shower (EAS). The 400 ENdetector array, so called ENDA (Electron-Neutron Detector Array), was proposed to add into the LHAASO (Large High Altitude Air Shower Observatory) project to improve its capability of EAS hybrid detection. ENDA will be located at the center of the first 1/4 of the KM2A surface scintillator array.

The electron and neutron detector (EN-detector) can detect the thermal neutrons produced by hadronic components in the secondary particles of cosmic rays. According to our previous paper about the performance of EN-detectors in Yangbajing, Tibet, during the period from August 2019 to January 2020, the number of detected neutrons in rain season is significantly (∼ 10%) lower than that in periods of dry season. In order to further study the correlation between the detector performance and humidity in soil, five soil moisture meters have been installed at different depths inside ENDA-16-HZS in August 2020. By analyzing the data in September 2020, it is demonstrated that both counting rate of EN-detector and neutrons in triggered events are negatively correlated with humidity.

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for the LHAASO CollaborationThe Large High Altitude Air Shower Observatory (LHAASO) project is a new generation EAS array, which will be built in Daocheng, Sichuan province, China at 4400m above sea level. With a wide field-of-view and high duty cycle, LHAASO will survey a large sky region in the declination band from -20 • to 80 • with a sensitivity of 10 mili-Crab per year at a much wider energy range from 100 GeV to 1 PeV. Besides increasing the number of VHE gamma-ray sources, it will also provide accurate spectrum measurement for the known γ-ray sources, especially for extended sources and transient phenomena. These are very important for us to look sight into γ-ray emission mechanism and particle acceleration within the sources. In this paper, we will investigate, basing on detector simulation, the ability of LHAASO on the measurement of spectra of SNRs, Cygnus region, diffuse galactic γ-rays and AGN flares.