The Silicon Tracking System of the CBM experiment at FAIR
J. Heuser1#1

GSI Helmholtz Center for Heavy Ion Research GmbH, 64291 Darmstadt, Germany# for the CBM Collaboration: E-mail J.Heuser@gsi.deThe Compressed Baryonic Matter experiment [1] at FAIR will explore the phase diagramof strongly interacting matter at highest net baryon densities and moderate temperatures. The
CBM physics program will be started with beams delivered by the SIS 100 synchrotron,
providing energies from 2 to 11 GeV/nucleon for heavy nuclei, up to 14 GeV/nucleon forlight nuclei, and 29 GeV for protons. The highest net baryon densities will be explored withion beams up to 45 GeV/nucleon energy delivered by SIS 300 in the next stage of FAIR.
Collision rates up to 107 per second are required to produce very rare probes with
unprecedented statistics in this energy range. Their signatures are complex. These conditions
call for detector systems designed to meet the extreme requirements in terms of rate capability,
momentum and spatial resolution, and a novel DAQ and trigger concept which is not limitedby latency but by throughput.
In the presentation we describe the concept and development status of CBM’s centraldetector, the Silicon Tracking System STS [2]. The STS realizes a large, highly granular andredundant detector system with fast read-out, and lays specific emphasis on low material
budget in its physics aperture to achieve for charged particle tracks a momentum resolution ofδp/p≈1% at p >1 GeV/c, at > 95% track reconstruction efficiency. The detector employs 1220
highly segmented double-sided silicon micro-strip sensors of 300 µm thickness, mounted into
896 modular structures of various types that are aggregated on 106 low-mass carbon fiber
ladders of different sizes that build up the tracking stations. The read-out electronics with its
supply and cooling infrastructure is arranged at the periphery of the ladders, and provides a
total channel count of 1.8 million. The signal transmission from the silicon sensors to theelectronics is realized through ultra-thin multi-line aluminum-Kapton cables of up to half ameter length. The electronics generates a free-streaming data flow of digitized time-stamped
detector information that is sent via data aggregator boards to the first-level event selector, acomputing farm for on-line event reconstruction. The power dissipated by the detector’s
read-out electronics, amounting to 2 times 20 kW in two thin layers at the top and bottom of
the detector, will be removed by a particularly efficient and space-saving bi-phase CO2cooling. The system integration of the detector takes respect of operating the sensors in athermal enclosure at -5ºC, to limit leakage currents originating from radiation damage, andallows for maintenance to the detector components, in particular the sensors, if they should
exceed an exposure to more than 1014 1 MeV neq/cm2. The detector system is built by a CBM
project team comprising institutes from Germany, Russia, Poland and Ukraine.
References[1] CBM web page, http://www.fair-center.eu/for-users/experiments/cbm.html[2] J. Heuser et al., Technical Design Report for the CBM Silicon Tracking System,
GSI Report 2013-4 (2013), http://repository.gsi.de/record/54798