The Compressed Baryonic Matter (CBM) heavy ion experiment is part of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. It is designed to probe the QCD phase diagram in regions of high baryon density. Its physics program includes studying the equation of state of nuclear matter at extreme densities, investigating the chiral symmetry restoration, and searching for signatures of phase transitions at 2.9 GeV ≤ √sN N ≤ 4.9 GeV.
The CBM detector is a single-arm forward spectrometer capable of process- ing data in a free streaming mode to handle unprecedented beam-target interac- tion rates of up to 10 MHz resulting from the continuous heavy-ion and proton beams from the SIS-100 accelerator at energies up to 11 AGeV and 29 GeV.
There are several detector subsystems for tracking, particle identification and event reconstruction in the CBM setup. The Silicon Tracking System (STS) as a core tracker of CBM plays an important role in all these tasks. It uses double-sided, double-metal silicon microstrip detectors with a dedicated SMX readout chip. Ultra-light aluminium-polyimide readout microcables transmit the analogue signals from the silicon sensors to the readout electronics located outside the sensitive volume: this allows the material budget to be reduced to about 8%X0, making STS comparable to gaseous detectors in terms of multiple scattering, while being several orders of magnitude faster. With performance studies largely completed, all CBM detectors are now in production.
Advanced detector technologies will allow CBM to measure the double- differential yields of multistrange hyperons and hypernuclei with unprecedented accuracy. It will also probe the higher-order fluctuations and flows to study the properties of the quark-gluon plasma at phase transition. In addition, a lightweight detector structure will allow clean statistically rich measurements of di-lepton spectra, enabling detailed studies of the thermal radiation of the medium and helping to map the in-medium modifications of hadrons.
