FOPI detector for heavy-ion collision experiment at SIS/GSI

The heavy-ion synchrotron (SIS) at GSI in Germany can accelerate various ions up to 2A GeV. The FOPI detector, the dedicated hadron spectrometer system, has been run in SIS for the last twenty years. The FOPI detector covers almost a full solid angle with two drift chambers and three scintillation counter arrays. The FOPI detector was recently fortified by a new time-of-flight (TOF) detector system that consists of the multi-strip multi-gap resistive plate chambers (MMRPCs). The intrinsic time resolution of the new TOF detector is less than 60 ps, and the improved time measurement in conjunction with the drift chamber information enables us to identify charged hadrons up to an unprecedented high momentum range. For example, the positive kaons can be identified up to 1.1 GeV/c, which is crucial to determining the in-medium effect of strange hadrons in dense matter. In this paper, we introduce the FOPI detector with emphasis on the new TOF system.