The space station based detector HERD: precise high energy cosmic rays physics and multimessenger astronomy

The High Energy cosmic-Radiation Detection (HERD) facility is one of several scientific payloads planned to go onboard China's Space Station, which is planned to be operational starting in around 2025 for about 10 years. The main scientific objectives of HERD are the search for signals of dark matter annihilation products, precise cosmic electron/positron spectrum and measurements of anisotropy up to 10 TeV, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy γ-ray monitoring and survey. HERD consists of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 7,500 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. The top STK microstrips of six X-Y layers are sandwiched with tungsten converters to measure with high efficiency incoming γ-rays. In the baseline design, each of the four side STKs is made of only three layers of microstrip detectors. All STKs will also be used for measuring the charge and incoming directions of electrons/positrons and cosmic rays, as well as identifying back scattered tracks. With this design, HERD can achieve the following performance: energy resolution of 1% for electrons and γ-rays beyond 100 GeV and 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10^-5; effective geometrical factors of > 3 m²sr for electrons and gamma-rays, > 2 m²sr for cosmic ray nuclei. Substantial activity is ongoing to optimize the detector parameters.