Particle physics plays an important role in understanding how stars, galaxies and other astrophysical objects work, and in studying the origin and evolution of the universe. Astrophysics and cosmology also pose great challenges for particle physics. The intersection between these fields is known as astroparticle physics (or particle astrophysics). IHEP is the biggest research base for astroparticle physics in China, focusing on cosmic rays, neutrino physics, astrophysics, space-based experiments, and underground experiments.

For cosmic ray experiments, the Yangbajing Cosmic Ray Observatory, in Tibet, is one of the four largest international ultra-high energy γ astronomy and ultra-high energy cosmic ray research arrays in the world. It hosts two experiment collaborations, the Sino-Japanese ASγ and Solar Neutron Experiment Collaboration, and the Sino-Italian ARGO-YBJ Collaboration. Evidence for the anisotropy of cosmic rays and for cosmic rays orbiting around the center of the galaxy was discovered by the Sino-Japanese ASγ experiment.

A much larger facility, the Large High Altitude Air Shower Observatory (LHAASO) has recently begun construction in Daocheng, Sichuan province (altitude 4410 m), with commissioning of the first phase expected in 2018. LHAASO will be used primarily for cosmic ray physics and gamma ray astronomy.

Space-based experiments in which IHEP is or has been involved include the Alpha Magnetic Spectrometer (AMS) experiments, a gamma-ray burst detector aboard the Shenzhou II spacecraft, the Chang’e series of lunar exploration missions, and the Hard X-ray Modulation Telescope (HXMT).

The AMS permanent magnet and its main structure, jointly developed by the Institute of Electrical Engineering, the Center for Space Science and Applied Research, the Chinese Academy of Launch Vehicle Technology and IHEP, were installed on the International Space in 2011. The experiment aims to search for the missing antimatter in the universe, to study high-energy cosmic rays, and to search for strangelets.

IHEP has been involved in all three Chang’e lunar missions. An X-ray spectrometer and solar monitor developed at IHEP were deployed aboard the Chang’e-1 satellite in 2007. The X-ray spectrometer measured X-rays in the range 10 – 60 keV over the mission’s 1-year lifetime, the first time the fluorescence X-ray spectrum of lunar elements was measured from lunar orbit. The X-ray spectrometer on board the Chang’e-2 satellite made the first observation of the characteristic fluorescent X-ray spectrum line of chromium on the lunar surface, and the first map of lunar surface aluminium. The Active Particle-induced X-ray Spectrometer (APXS), carried by the Chang’e-3 satellite’s “Jade Rabbit” lunar lander took X-ray fluorescence spectra of lunar regolith around the landing site.

The Hard X-ray Modulation Telescope (HXMT), a satellite-based X-ray telescope, aims to look for transient and variable X-ray sources in the galaxy, observe X-ray binaries to try and understand their behaviour in strong magnetic or gravitational fields, and study accreting black holes and neutron star systems. It is scheduled to launch in 2017.

IHEP also conducts research in astroparticle physics theory and phenomenology. We proposed super-Eddington accreting black holes as a new type of cosmic distance probe. With luminosity commonly bright than a supernovae by one or two orders of magnitude, these sources can serve as excellent distance candles to explore the critical era of the accelerating expansion of the Universe and unveil the nature and evolution of dark energy, thereby opening up a new window for observational cosmology.