Tracking fibre detectors based on solid state photomultipliers for PANDA

Solid state photomultipliers (SSPM) consist of a pixelised array of micrometric avalanche photodiodes connected in parallel. Despite the digital character of the signals from the individual pixels the device as a whole behaves analogically as long as the number of incoming photons remains small compared to the quantity of pixels. SSPM technology reduces even further the complexity and price of fibre tracking detectors by getting rid of voluminous high voltage power supplies and stiff cables used for conventional photomultipliers. In addition, such a detector will be insensitive to magnetic fields. The price to pay is a MHz dark count rate at room temperature. These events are generated by thermal electrons. Internal cross-talk between adjacent pixels can bring that noise to high amplitudes competing with real signals generated by a small number of photons. A small fibre barrel read-out by SSPM has been discussed as an option for a time-of-flight start detector in PANDA and as an active target for the hypernuclear physics programme in PANDA. Such a detector can be used for the particle identification, for a time reference for the DIRC detector, and for track deconvolution of the TP chamber [1]. The main purpose of the active hypernuclear target is the tracking and stopping of the produced Ξ hyperons and their decay products [1]. The detection efficiency has been measured using a Sr radioactive source for a two metres long cylindrical fibre, 0.89 mm in diameter and double cladding read out in both