SciFi: The New Scintillating Fibre Tracker for LHCb

The LHCb detector will be upgraded during the Long Shutdown 2 (LS2) of the LHC in order to cope with higher instantaneous luminosities and to read out the data at 40 MHz using a triggerless read-out system. The current LHCb main tracking system will not be able to cope with the increased particle multiplicities and will be replaced by a highly granular scintillating fibre detector. The new Scintillating Fibre (SciFi) tracker covers a total detector area of 340 m
²
and will provide a spatial resolution for charged particles better than 100 μm in the bending direction of the LHCb spectrometer. The detector will be built from individual modules (0.5 m × 4.8 m), each comprising eight fibre mats with a length of 2.4 m as active detector material. The fibre mats consist of six layers of 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 SiPMs after being exposed to a neutron fluence of up to 10
¹²
neq/cm
²
, expected for the lifetime of the detector, the SiPMs arrays are mounted on 3D-printed titanium alloy cold-bars placed in so called cold-boxes and cooled down to -40°C.