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Description
Summary
Luminosity monitoring is a critical component of any particle physics experiment, allowing one to compute the cross-section for the physical processes occurring in the detector. The luminosity measurement in CMS will be used to monitor the LHC beam and provide overall normalization for physics analyses. For off-line analyses in CMS, the design goal is a systematic accuracy of less than 10% for a range of beam luminosities from 1028cm-2s-1 to 1034cm-2s-1.
The CMS luminosity monitor is a system based on a mezzanine card called the HLX, mounted on the HCAL Trigger and Readout (HTR) board. It operates by histogramming data from the HTR boards for the forward hadronic (HF) calorimeters in CMS, which provide coverage from a pseudorapidity of 3 to 5 in both CMS end-caps. It computes both energy sums and counts of the number of physical towers below a preset energy threshold for this region, both of which can be extrapolated to measure luminosity. Combined with a careful off-line study, both the delivered and recorded luminosity can be measured. Using smaller sets of data, the real-time behavior of the system will be monitored online.
