The CMS Tracker Upgrade for the HL-LHC Tracking at Early Trigger Level

The performance of the tracker of the CMS experiment, comprising of a pixel and a strip detector, has so far been excellent, as reflected in the wealth of physics results produced so far. However, the foreseen increases of both the instantaneous as well as the integrated luminosity by the LHC during the next ten years will necessitate a series of upgrades of the CMS tracking detector. In 2016-17 the pixel detector will be exchanged, and around 2022 the whole tracker will need to be replaced, in order to be able to cope with an instantaneous luminosity of $5\times 10^{34}$~cm$^{-2}$s$^{-1}$ and an integrated luminosity of 3000~fb$^{-1}$, as expected for the High Luminosity LHC (HL-LHC). Experience at high luminosity hadrons collider experiments shows that tracking information enhances the trigger rejection capabilities while retaining high efficiency for interesting physics events. The design of a tracking based trigger for the HL-LHC is an extremely challenging task, and requires the identification of high-momentum particle tracks as a part of the Level~1 Trigger. The present status of this project is summarized, including the future tracker layout, the design of module prototypes, and the status of the front-end electronic components. Preliminary results of a simulated tracker layout equipped with stacked modules are discussed in terms of $p_{T}$ resolution and triggering capabilities.