Performance of the prototype Silicon Tracking System of the CBM experiment tested with heavy-ion beams at SIS18

TL;DR

This paper reports on the testing and evaluation of a prototype Silicon Tracking System for the CBM experiment, demonstrating its performance in heavy-ion beam experiments and its suitability for high-rate, high-precision particle tracking.

Contribution

It presents the design, implementation, and performance assessment of a prototype Silicon Tracking System for the CBM experiment, a key step towards full detector deployment.

Findings

Achieved over 95% tracking efficiency

Demonstrated momentum resolution better than 2% for >1 GeV/c

Validated detector performance in heavy-ion beam conditions

Abstract

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) is a heavy-ion experiment designed to study nuclear matter at the highest baryonic density. For high-statistics measurements of rare probes, event rates of up to 10 MHz are targeted. The experiment, therefore, requires fast and radiation-hard detectors, self-triggered detector front-ends, free-streaming readout architecture, and online event reconstruction. The Silicon Tracking System (STS) is the main tracking detector of CBM, designed to reconstruct the trajectories of charged particles with efficiency larger than 95%, a momentum resolution better than 2% for particle momenta larger than 1 GeV/c inside a 1 Tm magnetic field, and to identify complex decay topologies. It comprises 876 double-sided silicon strip modules arranged in 8 tracking stations. A prototype of this detector, consisting of 12 modules arranged in three tracking stations, is installed in the mini-CBM demonstrator. This experimental setup is a small-scale precursor to the full CBM detector, composed of sub-units of all major CBM systems installed on the SIS18 beamline. In various beam campaigns taken between 2021 and 2024, heavy ion collisions at 1-2 AGeV with an average collision rate of 500 kHz have been measured. This allows for the evaluation of the operational performance of the STS detector, including time and position resolution, hit reconstruction efficiency, charge distribution, signal-to-noise ratio, and its potential for track and vertex reconstruction.