SciFi, the new Tracker of the LHCb experiment

The LHCb Collaboration is currently in the final stage of constructing an upgraded detector that will allow the experiment to operate at higher luminosities and with a triggerless readout. The main tracking stations—which originally were subdivided in an Inner Tracker made from silicon strip sensors and an Outer Tracker built from straw-tubes—are being replaced by a single tracking detector, the Scintillating fibre Tracker (SciFi). The SciFi covers a total detector area of 340 m$^{2}$by using more than 10000 km of scintillating fibre with 250 μm diameter, enabling a spatial resolution of better than 100 μm for hits originating from charged particles. It is built from individual modules (0.5 m × 4.8 m) comprised of 8 scintillating fibre mats with a length of 2.4 m as the active detector material. The 13 cm wide fibre mats consist of 6 layers of densely packed blue emitting scintillating fibres. The scintillation light is detected with arrays of multi-channel silicon photomultipliers (SiPMs) cooled to −40ˆC to minimize the expected high dark noise from neutron radiation. The readout of 524k channels occurs through custom-designed front-end electronics. Since it is the first time that this technology is being used as a large tracker and with a small granularity, many challenges have to be overcome. This document is intended to give an overview of the SciFi detector design, production, performance and the status of the detector assembly.