Emittance scans for CMS luminosity calibration

Emittance scans are short van der Meer type scans performed at the beginning and at the end of LHC fills. The beams are scanned across each other in x and y planes. CMS has analyzed these scans to understand long-term trends in CMS luminosity detectors. The CMS Beam Radiation, Instrumentation and Luminosity (BRIL) project provides to LHC three independent online luminosity measurements from the Pixel Luminosity Telescope (PLT), the Fast Beam Condition Monitor (BCM1F) and the Forward Hadronic calorimeter (HF). The excellent performance of the BRIL detector front-ends, fast back-end electronics and CMS XDAQ based data processing and publication allow the use of emittance scans for linearity and stability studies of the luminometers. Emittance scans became a powerful tool and dramatically improved the understanding of the luminosity measurement during the year.