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The HL-LHC will increase the delivered luminosity to the CMS experiment allowing it to broaden its physics reach. The average number of pileup interactions will increase to 200 in the detector meaning the current trigger systems will be unable to maintain their selectivity for electroweak physics. To maintain manageable trigger rates, silicon-tracker based tracking at 40 MHz is to be included in the Level-1 trigger for the first time. To achieve data rates low enough for track triggering the CMS outer tracker will use modules with closely-spaced silicon sensors which will only read out hits compatible with charged particles with a transverse momentum, pT, above 2 GeV/c. These hits will be used in the backend Level-1 track finding system built on commercially available FPGA technology to reconstruct the charged particle tracks. The track finding algorithm is split into a track seeding stage forming tracklets from pairs of stubs and a Kalman Filter fitting algorithm to identify final track candidates and determine track parameters. The implementation of this algorithm in firmware is ongoing and a preliminary demonstration of the system in hardware is discussed.
Christopher Brown (Wed,) studied this question.