The Silicon Tracking System of the CBM Experiment at FAIR

Abstract

The Compressed Baryonic Matter (CBM) experiment at FAIR will conduct a systematic research program to explore the phase diagram of strongly interacting matter at highest net baryon densities and moderate temperatures. These conditions are to be created in collisions of heavy-ion beams with nuclear targets in the projectile beam energy range of 2 to 45 GeV/nucleon, initially coming from the SIS 100 synchrotron (up to 14 GeV/nucleon) and in a next step from SIS 300 enabling studies at the highest net baryon densities. Collision rates up to 10 7 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 data acquisition and trigger concept which is not limited by latency but by throughput. In the paper we describe the concept and development status of CBM's central detector, the Silicon Tracking System (STS). The detector realizes a large, highly granular and redundant 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 of δp/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 the electronics is realized through ultra-thin multi-line aluminum-polyimide cables of up to half a meter length. The electronics generates a free-streaming data flow of digitized time-stamped detector information that is sent via data aggregation boards to the first-level event selector, a computing farm for on-line event reconstruction. The power dissipated by the detector's read-out electronics, amounting to about 2 times 20 kW in two layers at the top and bottom of the detector, will be removed by a particularly efficient and space-saving bi-phase CO 2 cooling. The system integration of the detector takes respect of operating the sensors in a thermal enclosure at -5 • C, to limit leakage currents originating from radiation damage, and allows for maintenance to the detector components, in particular the sensors, if they should exceed an exposure to more than 10 14 1 MeV n eq /cm 2 . The detector system is developed and built by a CBM project team comprising institutes from Germany, Russia, Poland and Ukraine.

Non-invasive characterization and quality assurance of silicon micro-strip detectors using pulsed infrared laser

“…The detector modules will be read-out through a low mass multi-line fine-pitch flat cables by a front-end electronics located outside of the physics acceptance at the periphery of the STS stations. The approved technical design report of the STS can be found here [6].…”

The Compressed Baryonic Matter experiment

“…It consists of 8 stations of thin and high resolution double-sided silicon strip sensors, stabilized by a low mass carbon support structure [14]. The detector layout can be seen in Figure 7.…”

“…[14]) or in the process of submission. The construction phase of the FAIR accelerator is planned to end in 2017, when the experiment apparatus will be installed in the CBM cave.…”

“…Figure 7. Layout of the Micro-Vertex Detector (left side), placed inside a vacuum vessel (depicted in orange), followed by the Silicon Tracking System [14]. The latter is composed of 8 stations placed from 30 cm to 1 m from the target (and separated by a step of 10 cm).…”

Quality Assurances for Silicon Double sided Sensors in Silicon Tracker System for CBM Experiment at FAIR

“…The Silicon Tracking System (STS) is the central detector system of the future Compressed Baryonic Matter (CBM) experiment [1] at the Facility for Anti-proton and Ion Research (FAIR) [2], Darmstadt, Germany. STS faces numerous challenges [3] including the design constraints, tracking in high magnetic field, high precision in momentum resolution of p/p ≈ 1%, high radiation load ≈1×10 14 n eq /cm 2 for SIS-300 energies, up to 1000 charged particles/interaction at rates of ≈ 10 MHz/cm 2 and to run a self-triggered front end electronics (FEE) to read 2 million channels (or strips). These constraints and severe conditions makes it significantly important to have a systematic quality assurance (QA) to investigate, test and exclude the silicon sensors on the basis of acceptance criteria determined by the experimental operational requirements.…”