Development of a Level 1 Track Trigger for the CMS Experiment at the High-Luminosity LHC

Over the next decade, several upgrades in the LHC and its injector chain will eventually increase the luminosity by up to a factor of $10$ compared to the original design figure of $10^{34}$ cm$^{-2}$s$^{-1}$. In order to cope with the large number of interactions per bunch crossing, a novel tracking system for the CMS experiment will be designed and built. The new tracker will also provide information to the Level 1 trigger decision, in order to improve the ability of selecting interesting physics channels in a higher density environment. The CMS collaboration is developing a novel module concept (``$p_T$-module''), where signals from two closely-spaced sensors are correlated in the front-end electronics, to select pairs of hits compatible with particle $p_T$ above a certain threshold. Selected pairs of hits, called ``track stubs'', represent between $5\%$ and $10\%$ of the overall data rate: such reduction factor enables the data processing at Level 1. Two main types of $p_T$-modules are being developed, one based on strip sensors, and the other coupling a strip sensor with a pixelated sensor, which provides also precise information in the $z$ coordinate. The main features of the $p_T$-module options under development are reviewed, as well as the benchmark results from simulation studies.