The LHCb Upgrade Scintillating Fibre Tracker

The Scintillating Fibre (SciFi) Tracker is designed to replace the current downstream tracking detectors in the LHCb Upgrade during 2018 (CERN/LHCC 2014-001; LHCb TDR 15). The operation and the results obtained from the data collected 2011 and 2012 demonstrate that the current detector is robust and functioning very well. However, the limit of O ( 1 fb-1) of data per year cannot be overcome without improving the detector. This will be achieved using 25 ns bunch spacing with the average number of proton-proton interactions per bunch crossing n = 7 : 6. Collecting data at this luminosity will only be possible if the detector is improved by increasing the readout of the front-end electronics to 40MHz and implementing a more flexible software-based triggering system that will increase the data rate as well as the efficiency. The increase in interactions per bunch crossing will result in an increased occupancy in the tracking detectors and will exceed the operational occupancy for the Outer Tracker. Here we present the SciFi Tracker as the replacement for the Outer and Inner Trackers. The SciFi Tracker is based on 2.5 m long multi-layered ribbons from ( 7 10 3 km) of 0.250 mm diameter scintillating fibre as the active medium and signal transport over 12 planes covering 375 m 2 . Cooled silicon photomultiplier (SiPM) arrays with 128 channels and 0.25 mm channel width are used as readout. The front-end electronics are designed to digitise the signals from the SiPMs with a custom ASIC chip, the PACIFIC, for the approximately 590k channels and reconstruct the track hit position within an on-board FPGA. Several challenges facing this detector will be presented regarding the precision construction of the large active detector components, the radiation hardness of the scintillating fibres and the SiPMs, the high density readout electronics, and the necessary cooling systems.