The silicon tracker of the CBM experiment at FAIR: Detector developments and first in-beam characterizations

The Silicon Tracking System (STS) is a key detector of the CBM experiment planned at the Facility for Antiproton and Ion Research (FAIR). It has to reconstruct the trajectories of hundreds of charged particles created in heavy-ion collisions at typical beam energies of 25 GeV/nucleon. Radiation hard sensors and fast read out electronics are needed to match the interaction rates of up to 10 MHz. A low-mass detector system is required for a momentum measurement with about 1% resolution. First double-sided silicon microstrip detector prototypes with 50 ¿m strip pitch developed together with CiS, Germany have been characterized in the laboratory and several in-beam tests. In a full read-out chain based on self-triggering front-end electronics they were operated at GSI in a 2 GeV proton beam. A demonstrator tracking station was integrated into the beam tracker of the SVD-2 experiment at IHEP, Protvino, Russia and tested in a 50 GeV proton beam. The CBM experiment will operate with a high-intensity DC beam at the FAIR synchrotron SIS-300. Fast front-end electronics and a high-throughput data acquisition system are required. The self-triggering n-XYTER read-out chip with 128 channels is being explored in the prototype system tests. We present results on the detector response and the behavior of front-end electronics in a full data acquisition chain. The high-radiation environment in the CBM experiment results in a particle fluence through the STS of up to 10¹⁵ 1-MeV n_eq/cm² per year. We present measurements of double-sided silicon microstrip detectors as well as PiN diodes irradiated up to 10¹⁴ 1-MeV n_eq/cm² and compare them to non-irradiated samples.