L1 Track Triggering at CMS for High Luminosity LHC

The High Luminosity LHC (HL-LHC) is expected to deliver luminosities of $5 \times 10^{34}$~cm$^{-2}$s$^{-1}$, with an average number of overlapping proton-proton collisions per bunch crossing (pileup) of about 140. These extreme pileup conditions place stringent requirements on the experiments' trigger systems to cope with the resulting event rates. For the CMS experiment, a key component of the detector upgrade for the HL-LHC is a track-trigger system which would identify tracks with transverse momentum above 2 GeV already at the first-level (L1) trigger. Here, a proposal for implementing L1 tracking using "tracklets" is presented. The expected performance of the L1 tracking from simulation studies and the use of L1 tracks to define trigger objects are discussed