Layout studies and sensor prototypes for the CBM Silicon Tracking System

The Silicon Tracking System (STS) is the central detector of the CBM experiment. It serves for track reconstruction with good momentum measurement (of about of 1%) of all charged particles produced in high multiplicity nuclear reactions at the target [1]. For this task a lowmass silicon tracking detector system of high granularity is needed. We are currently studying the arrangement of the tracking stations and designing the prototype of the microstrip silicon detectors. The STS concept, schematically shown in Fig. 1, comprises 6 detector stations for the track measurement, made of micro-strip silicon detectors. Each station is divided into sensors, with short strips close to the beam line (compare Fig. 2) and with longer strips, realized either on single wafers or by chaining two or more sensors, in the regions further outside. The reading of the individual sensors may be realized by routing the strips’ analog signals from every sector through thin flat multi-line cables to front-end electronics at the periphery of the stations (see current R&D effort in [2]). The projective coordinate measurement of the sensors leads to a significant fraction of combinatorial or fake hits, a challenge to the reconstruction algorithms. In alternative approach two first stations may consist of LHCtype hybrid pixel detectors, although those are relatively thick and presumably require active cooling in the aperture. For high-resolution vertex measurements, e.g. open charm detection, the STS is supported with a Micro-Vertex Detector (MVD) consisting of two very thin and fine-pitch MAPS pixel detector stations close to the target.