A Level 1 Tracking Trigger for the CMS Experiment

The LHC machine is planned to be upgraded in the next decade in order to deliver a luminosity about 5 to 10 times larger than the design one of $10^{34}$ cm$^{-2}$s$^{-1}$. In this scenario, a novel tracking system for the CMS experiment is required to be conceived and built. The main requirements on the CMS tracker are presented. Particular emphasis will be given to the challenging capability of the tracker to provide useful information for the Level 1 hardware trigger, complementary to the muon system and calorimeter ones. Different approaches based on pattern hit correlation within closely placed sensors are currently under evaluation, making use of either strips or macro-pixels. A proposal to optimize the data flow at the front-end ASIC and develop a tracking algorithm to provide tracks at Level 1 will be presented.