Upgrades of the CMS Outer Tracker for HL-LHC

The LHC machine is planning an upgrade program which will smoothly bring the luminosity to about 5×1034cm$^{−2}$s$^{−1}$ around 2028, to possibly reach an integrated luminosity of 3000 fb$^{−1}$ in the following decade. This High Luminosity LHC scenario, HL-LHC, will require a preparation program of the LHC detectors known as Phase-2 upgrade. The current CMS Outer Tracker, already running close to its design limits, will not be able to survive HL-LHC radiation conditions and CMS will need a completely new device, in order to fully exploit the highly demanding operating conditions and the delivered luminosity. The new Tracker should have also L1 trigger capabilities. To achieve such goals, R&D; activities are ongoing to explore options and develop solutions that would allow including tracking information at Level-1. The design choices for the CMS Outer Tracker upgrades are discussed along with some highlights of the R&D; activities.