The prototype of the Aachen Muon Detector was designed as an alternative for the upcoming upgrade (AugerPrime) of Scintillating Surface Detectors (SSD) for the Pierre Auger Observatory. Due to the successful application of semi-conductor photo sensors (SiPM), two portable detectors with a slightly modified design were built. They are currently applied for testing the local production of SSD detectors.
Each of the two detectors consists of eight 30 x 30 x 0.5 cm$^3$ scintillator tiles. The light of each tile is collected by a dedicated wavelength-shifting fiber embedded into the tile and coupled directly to a 1.3 x 1.3 mm$^2$ SiPM. Reading out each channel individually with an EASIROC data acquisition chip provides spatial resolution, muon counting and an amplitude measurement for bright events. The obtained spectrum of minimum ionizing particles is nicely modulated with the single-photon equivalent (p.e.) resolution of the SiPM allowing for a very precise calibration of the system.
The use of SiPM provides a very robust solution for a lightweight and portable detector easily applicable to a wide variety of setups.