Development and Characterisation of Silicon Photomultiplier Multichannel Arrays for the Readout of a Large Scale Scintillating Fibre Tracker

The current LHCb detector will continue collecting data until the long shutdown 2 (2019/2020). It will be upgraded in order to operate at higher luminosity. To achieve this, two major changes are required. First the Level-0 hardware trigger limited to 1,MHz will be replace by a trigger-less data acquisition running at 40,MHz. Secondly, the tracking system will be upgraded to cope with the higher track density and the required granularity. The Inner Tracker (silicon strip) and Outer Tracker (straw drift tubes) will be replaced with a single large area (300$\rm{m^2}$) scintillating fibre tracker (SciFi). The tracker is based on scintillating fibres read out by silicon photomultipliers (SiPM). A custom front-end chip has been designed for a fast readout.

This work presents the SiPM developments and motivates the choice of the selected technology. The SiPM technology is used for its high photo detection efficiency (PDE) and its single photon sensitivity due to its intrinsic high gain. Different technologies from two manufacturers, Hamamatsu and KETEK, were tested and compared. A detailed characterisation is presented for the selected design. The breakdown voltage, gain, temperature dependency, correlated noise, dark count rate (DCR) and PDE were found to fulfil the requirements for this application. The device reveals a peak PDE of 45% at the benchmark operation point.

SiPMs are radiation sensitive. The neutron fluence in the detector location increases dramatically the noise which was studied in many irradiation campaigns. The expected effect was found to be acceptable for the LHCb requirement.

This work focuses on novel SiPM characterisation methods that were developed for LHCb. In particular, a pulse shape statistical analysis to measure correlated noise probabilities, time constants and noise correction factors is presented. Setups to measure the PDE, from pulse frequency measurement, and the DCR, from IV measurements, were also developed.

The SciFi technology has an excellent application potential as for example beam tracking instrumentation. A telescope composed of four x-y scintillating fibre tracking stations is also presented. A track resolution of 16\mum was achieved with a single hit spatial resolution of 36\mum.

A simulation study implementing an optical focusing system at the SiPM micro-pixel using micro-lenses is presented. The micros-lenses allow to decrease the light loss at the dead areas and has the potential to reduce the total active area.

At the current state of production 20% of the 5500 SiPMs required for the LHCb SciFi have been fully electrically tested and geometrically and optical inspected. The detectors are selected in groups featuring similar breakdown voltages, to be assembled on the cooling bars.