High-precision luminosity instrumentation for the CMS detector at the HL-LHC

Abstract

The high-luminosity upgrade of the LHC (HL-LHC) is foreseen to reach an instantaneous luminosity a factor of five to seven times the nominal LHC design value. This creates the need for new high-precision instrumentation at CMS, using radiation-hard detector technologies. This contribution introduces the instrumentation for bunch-by-bunch online luminosity and beam-induced background measurements in CMS. The Tracker Endcap Pixel Detector (TEPX) will be adapted for precision luminometry by implementing a dedicated trigger type and a real-time data processing system performing clustering on FPGA. The innermost ring of the last TEPX layer (D4R1) will be operated independently from the rest of TEPX, enabling beam monitoring during the LHC ramp and during unqualified beam conditions with a dedicated timing and trigger infrastructure. A new standalone luminometer, the Fast Beam Condition Monitor (FBCM), which will be fully independent from the central trigger and data acquisition services and will be able to operate during all times is also introduced. FBCM is foreseen to utilize silicon-pad sensors with sub-bunch-crossing time resolution enabling also the measurement of beam-induced background. The potential of the exploitation of other CMS subsystems such as the outer tracker, the barrel muon detectors and the 40 MHz L1 trigger scouting system using a common histogramming firmware is also discussed.