CMS Activities Detector Operation Beam Monitoring and Luminosity  · 

Beam Monitoring (BCM1F) and Luminosity Measurement

The DESY group engages in the measurement of the LHC luminosity, both online during the data taking, and offline, in the precision determination of the integrated luminosity recorded.

Online Beam Condition Monitoring

The CMS Fast Beam Condition Monitor (BCM1F) is a subdetector dedicated to the online measurement of the luminosity and to the monitoring of beam-related background rates. BCM1F consists of 24 sensors (diamond and silicon) of 5×5 mm2 area each, mounted on two rings close to the beam pipe at a distance along the beam pipe of 1.8 m on each side of the interaction point. Due to the excellent time resolution of the device, signals from proton-proton collisions can be distinguished from background signals on a bunch-by-bunch basis using their arrival time. By use of a fast real-time histogramming unit, BCM1F delivers a measurement of the instantaneous luminosity and the background rate to the CMS and LHC control rooms, independently of the operational state of the CMS experiment. It also provides a fast beam-abort system for protection of the CMS track detectors. The DESY group plays a leading role in the operation of the device, including commissioning, calibration and day-to-day operation.

Measurement of the Integrated Luminosity

DESY contributes to the precision measurement of the integrated luminosity. This measurement has two components: By evaluation of Van-der-Meer scans (figure on the right taken from this note), an absolute scale is determined. The integrated luminosity is then obtained by integration of continuous rate measurements during data taking with regular collisions.



There are ample opportunities for contributions at all levels, both in the operation, study and calibration of the detector as well as in the analysis of the offline data. For further details, please email

Last updated on 17-10-2017


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