The Development and Performance of the Pixel Luminosity Telescope at the CMS experiment of the LHC

The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN, Conseil Européen pour la Recherche Nucléaire) was in an upgrade period (LS2, Long Shutdown 2) since 2018 in preparation for the new data-taking period (Run 3) that started by early 2022. During LS2, the Beam Radiation Instrumentation, and Luminosity (BRIL) group of the Compact Muon Solenoid (CMS) experiment, rebuilt one of its main detectors, the Pixel Luminosity Telescope (PLT), to perform highly precise measurement of the luminosity. This quantity, which is related to the amount of data collected by the experiment, is used in nearly every physics data analysis and it is crucial for the success of the LHC and CMS physics programs to measure it as accurately as possible. The PLT is a dedicated luminometer based on silicon pixel technology that consists of 48 sensor planes arranged into 16 “telescopes” of three planes each, with eight telescopes positioned around the beam pipe of the accelerator at either end of the CMS detector. It is located at a distance of approximately 1.75m from the nominal interaction point of the two particle beams that circulate the LHC. The planes in a telescope are positioned such that a particle coming from the collision point of the two beams will produce a signal in each of the three planes. The instantaneous luminosity is measured from this rate of triple coincidences, using a special “fast-or” readout, at the full bunch-crossing rate of 40 MHz, allowing for real-time, accurate luminosity information to be provided to CMS and the LHC. Besides the fast-or, there is a second readout mode using the full pixel information, hit position, and charge. It reads out at a lower rate and can be used to study systematic effects in the luminosity measurement. In this thesis, the work carried out to build a new version of PLT for Run 3 is detailed. First, the individual components of the detector and its operating principles are introduced. Then, the testing, validation, characterization, and selection procedures of the pixel sensors, including their quantitative analysis, are presented. Techniques on hardware failure detection, inspection, and resolution of back-end and front-end hardware of the detector, its assembly, and its stress testing process are outlined. Finally, the installation of the new PLT in the CMS detector, performed in July 2021, its checkout, calibration, and commissioning are discussed

The Pixel Luminosity Telescope: a detector for luminosity measurement at CMS using silicon pixel sensors

International audienceThe Pixel Luminosity Telescope is a silicon pixel detector dedicated to luminosity measurement at the CMS experiment at the LHC. It is located approximately 1.75 m from the interaction point and arranged into 16 “telescopes”, with eight telescopes installed around the beam pipe at either end of the detector and each telescope composed of three individual silicon sensor planes. The per-bunch instantaneous luminosity is measured by counting events where all three planes in the telescope register a hit, using a special readout at the full LHC bunch-crossing rate of 40 MHz. The full pixel information is read out at a lower rate and can be used to determine calibrations, corrections, and systematic uncertainties for the online and offline measurements. This paper details the commissioning, operational history, and performance of the detector during Run 2 (2015–18) of the LHC, as well as preparations for Run 3, which will begin in 2022