Introduction

　　YBJ International Cosmic Ray Observatory is located at 90°26'E and 30°13'N in Yangbajing (YBJ) valley of Tibetan highland, near the cross point of Qinghai – Tibet and China - Nepal highways, and the Qinghai - Tibet railway (to be completed in 5 years), about 90 km away from the city of Lhasa. YBJ's wide and flat topography, convenient traffic, scarce heavy snow, rich geothermal power source, about 4,000 residents and many neighboring institutions & services, make it the best site of high altitude observatory in the world.

　　YBJ Observatory was founded in 1990. It has hosted the Tibet ASγ Experiment (Sino-Japanese Cooperation) ever since. After 6 years’ preparation, the ARGO -YBJ Project (Sino-Italian Cooperation) started its detector installation in 2000. Both of them aim at the research of the origin of high energy cosmic rays, the GRB physics in high energy, the correlation between the movement of the Cosmic ray sun shadow and the solar/interplanetary magnetic field and solar activity, etc.  Through the observation of air showers (AS) by AS array - a semi-full sky and continuous observation technique. Taking advantage of the YBJ high altitude, by increasing the density of scintillation detector, the ASγ Array has successfully observed γ rays from Crab Nebula and Mrk 501 (during its flaring period in 1997); by developing the traditional sampling AS array as a "carpet", the ARGO-YBJ full coverage array is intended for exploring the approximately 100 GeV uncultivated land and measuring the antiproton/proton ratio by cosmic ray moon shadow.
　　  Beside the AS array, neutron monitor and neutron telescope have been available for solar and hiliosphere study. Along with the further development of the observatory, the existing detectors will be upgraded and more new type detectors adopted.

　　Sino – Japanese Cooperation on AS and Solar Neutron Experiment

The purpose of this cooperative experiment is as follows:

1) to search and monitor the Gamma ray sources with the energy threshold of 3TeV.

2) to study the configuration and variation of the solar and interplanetary magnetic fields under the influence of the solar activity by monitoring on time variation of the Sun shadows of cosmic rays.

3) energy spectrum around the composition study and the "knee" of primary cosmic rays.

4) to monitor the time variation of cosmic rays with the energy larger than 14 GeV detect the solar proton and neutron events and study the solar modulation of galactic cosmic rays and the production process of high energy particles in solar flares or CMEs.

　　Taking part in this international cooperation on the Chinese side are the Institute of High Energy Physics (IHEP), CAS Center for Space Science and Applied Research, CAS; Shandong University; Southwest Jiaotong University; Tibet University and Yunnan University with Professor Youheng Tan being the spokesman, on the Japanese side are Hirosaki University; Utsunomiya University; Saitama University; Shibaura Institute of Technology; University of Tokyo; Tokyo Metropolitan College of Aeronautical Engineering; National Institute of Information; Waseda University; Kanagawa University; Yokohama National University; Shonan Institute of Technology; Nagoya University and Konan University with Professor Toshinori Yuda being the spokesman.　　

Sino–Italian International Cooperation on ARGO-YBJ Experiment

　　ARGO-YBJ (Astroparticle - physics Research at Ground-based Observatory Yangbajing) Experiment is to be carried out at high altitude YBJ Observatory which boasts a 5000 m² full coverage carpet-like RPC array to realize the low threshold energy high sensitivity detection of the primary γ-ray and cosmic ray particles. The RPC array covers a vast range of sky (-10°<δ<70°) and energy region (10GeV-100TeV) with the ground based full time duty AS array technique. Such characters can be vividly depicted with the mythological monster of ARGO, who has many eyes and never sleeps.
　　 The ARGO -YBJ project was launched by Chinese and Italian scientists in 1994. Their common efforts led to the successful testing of 50m² RPC carpet at YBJ in the winter season of 1997/1998 and the conclusion of the official agreement between the two governments of China and Italy on this cooperation in 1998. A 10,000 m² ARGO hall was accomplished in YBJ Observatory in 2000, thus making possible for the installation of RPC and electric network to start. According to schedule, the whole carpet will be completed and put into operation in 2003.

 Research Goals

 Based on the low energy threshold (~100GeV), high sensitivity (~0.1 of Crab flux) and a fine granularity space-time picture of shower front provided by the YBJ high altitude and the full coverage detector array, the following scientific goals will be achieved:

 1) Gamma-ray astronomy: Continuous monitoring of the γ-ray sources in the northern sky at a 100 GeV threshold energy to bridge the "satellite regime" to the multi-TeV region by a full time and wide FOV detector, with a sensitivity ~1/10 Crab flux. More attention will be paid to about 100 GeV and several 10 TeV region, where either it is the region which has never been explored before or the region where a γ-ray source corresponding to a UHE hardron acceleration site can be found out;

 2) Diffuse –γ rays: From the Galactic plane, molecular clouds and Supernova Remnants at 3100 GeV have never been observed so far;

 3) Gamma ray burst physics: Extending the satellite measurements over the full GeV/TeV range;

 4) Antiproton/proton ratio measurement: At about 1 TeV (inaccessible to satellites), with a sensitivity adequate to distinguish between models of local (galactic) proton production and model accounting for an extragalactic origin;

 5) Sun and heliosphere physics, including cosmic ray modulation at about 14 GeV threshold energy, continuous monitoring of the interplanetary magnetic field on monthly scale, detection of high energy Gamma and neutron flares;

 6) Detailed study of air shower in the energy range of 1012-1015 eV, including the fine structures of air shower and some peculiar features in the extreme forward region of UHE interaction, based on the unprecedented details of individual air showers recorded by ARGO-YBJ carpet;

 7) Measurement of the primary proton spectrum: In the 10 – 200 TeV region, the traditional balloon experiment regime, with much smaller error bars and a sensitivity sufficient to detect a possible change of the proton energy spectrum.

　　Taking part in this collaboration on the Chinese side are the Institute of High Energy Physics, CAS; Center for Space Science and Applied Research, CAS; Shandong University; Southwest Jiaotong University; Tibet University and Yunnan University, with Professor Tan Youheng being the spokesman of the Chinese side. Taking part in this collaboration on the Italian side are INFN and Lecce University; INFN and Napoli University; INFN Section of Napoli and University of Salerno; INFN Section of Napoli and University of Sonnio, Benevento; INFN and University Roma "Tor Vergata"; INFN and University "Roma Tre" Roma; INFN and Institute of Cosmogeo Physics of CNR, Torino; INFN Section of Catania and Institute of Physics of Cosmic and IFCA/CNR,Palerno and INFN Section of Pavia, with Professor Benedetto D'Ettorre Piazzoli being the spokesman of the Italian side