Developing silicon pixel detectors for LHCb: constructing the VELO Upgrade and developing a MAPS-based tracking detector

  • Dónal Murray

Student thesis: Phd


The Large Hadron Collider beauty (LHCb) experiment is currently undergoing a major upgrade of its detector, including the construction of a new silicon pixel detector, the Vertex Locator (VELO) Upgrade. The challenges faced by the LHCb VELO Upgrade are discussed, and the design to overcome them is presented. VELO modules have been produced at the University of Manchester. The VELO modules use 55 micron pixels operating 5.1 mm from the beam without a beam pipe, an innovative silicon microchannel cooling substrate, and 40 MHz readout with a full detector bandwidth of 3 Tb/s. The module assembly process and the results of the associated R&D are presented. The mechanical and electronic tests are described. A grading scheme for each test is described, and the results are presented. The majority of the modules are of excellent quality, with 40 out of 43 of suitable quality for installation in the experiment. A full set of modules for the experiment has now been produced. The VELO Upgrade is read out into a data acquisition system based on an FPGA board. The architecture of the readout firmware for the readout FPGA for the VELO Upgrade is presented, and the function of each block described. Challenges arise due to the design of the VeloPix front end chip, the fully-software trigger and real-time analysis paradigm. These challenges are discussed and their solutions briefly described. An algorithm for identifying isolated clusters is presented and previously-considered approaches discussed. The current design uses around 83% of the available logic blocks, and 85% of the available memory blocks. A complete version of the firmware is now available and is being refined. An ultimate version of the LHCb experiment, the LHCb Upgrade II, is being designed for the 2030s to fully exploit the potential of the high luminosity LHC. The Mighty Tracker is the proposed new combined-technology downstream tracker for Upgrade II, consisting of a silicon pixel inner region and a scintillating fibre outer region. A potential layout of the detector and modules is given. The silicon pixels will likely be the first LHC tracker based on radiation-hard HV-MAPS technology. Studies for the electronic readout system of the silicon inner region are reported. The total bandwidth and its distribution across the tracker are discussed. The numbers of key readout and FPGA DAQ boards are calculated. The detector’s expected data rate is 8.13 Tb/s in Upgrade II conditions over a total of more than 46,000 front end chips.
Date of Award1 Aug 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorChristopher Parkes (Supervisor) & Marco Gersabeck (Supervisor)

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