First test of a prototype CBM silicon detector system in a proton beam at GSI

In September 2008, the CBM collaboration performed the first essential test of two prototype detector systems in a 2.5 GeV proton beam at GSI. The experiment at the HTD beam line in Cave C comprised prototype micro-strip detectors of the Silicon Tracking System, and gas-electronmultiplier (GEM) detectors. The detectors were coupled to a self-triggering front-end electronics and data acquisition system. This novel data read-out and acquisition concept is being developed for nuclear interaction rates of up to 10 millions per second. It aims at enabeling the online reconstruction of collision events with up to 1000 produced particles. In a further measurement the radiation tolerance of Field Programmable Gate Arrays (FPGAs) was investigated. The silicon detector setup is shown in Fig. 1. It comprised two detector boards equipped with prototype microstrip sensors CBM01 developed by the GSI-CBM group and CIS Erfurt [1], and two readout boards developed at GSI around the n-XYTER [2] chip, developed in a different project. The readout chain included further Syscore controller boards [3] for communicating with the n-XYTER electronics, and the GSI data acquisition system DABC [4]. The commissioning of the silicon detector system was performed with a radioactive source. The ADC spectra of several readout channels are shown in Fig. 2. Response to the proton beam is shown in Fig. 3. The correlation of fired horizontal and vertical strips from the up-stream and the down-stream detector is clearly visible, only linked through the time measurement done by the front-end electronics. The test demonstrated the validity of the CBM data acquisition concept based on detector systems read out with self-triggering front-end electronics. Three different detector partitions were commonly read out. The full data chain was successfully realized, from the detectors’ front end to data in the acquisition system’s raw format and FairRoot format, allowing for on-line monitoring during the experiment and subsequent detailed off-line analysis. For the characterization of forthcoming prototype components of the CBM Silicon Tracking System, a reference tracking telescope is under preparation.