A large Scintillating Fibre Tracker for LHCb

The LHCb detector is currently being upgraded in order to cope with higher instantaneous luminosities and to read out the data at 40MHz using a trigger-less read-out system. The Run 1 + 2 tracking system, composed of an inner and outer tracking detector, will not be able to cope with the increased particle multiplicities and is being replaced by a single homogenous detector based on scintillating fibres. The new Scintillating Fibre (SciFi) Tracker covers a total detector area of 340 m2 and should provide a spatial resolution for charged particles better than 100 µm in the bending direction of the LHCb spectrometer. The detector is being built from individual modules (0.5 m × 4.8 m), each comprising 8 scintillating fibre mats with a length of 2.4 m as active detector material. The fibre mats consist of 6 layers of densely packed blue emitting scintillating fibres with a diameter of 250 µm. The scintillation light is recorded with arrays of state-of-the-art multi-channel silicon photomultipliers (SiPMs). A custom ASIC will be used to digitize the SiPM signals. Subsequent digital electronics performs clustering and data-compression before the data is sent via optical links to the DAQ system. To reduce the thermal noise of the SiPM in particular after being exposed to a neutron fluence of up to 1012 neq /cm2, expected for the lifetime of the detector, the SiPMs arrays are mounted in so called cold-boxes and cooled down by 3D-printed titanium cold-bars to -40o C. Modules together with cold-boxes and readout electronics are mounted on so-called C-frames which provide the mechanical support structure and the necessary services to power, read out and cool the detector elements. After a first proto-type frame has been built and tested the serial assembly of these detector elements has started in March 2019. The first finished and commissioned detector elements will be installed in the experimental cavern at the end of 2019. The talk will give an overview of the detector concept and will present the experience from the series production complemented by most recent test and comissioning results.