2S modules for the Phase-2 upgrade of the CMS tracker

The CMS experiment at the Large Hadron Collider LHC will face a new era after Long Shutdown 3, which is scheduled to take place between 2024 and 2026. The challenge of running a tracking detector at the High Luminosity LHC will be the high instantaneous luminosity of $5\times10^{34}$ s$^{-1}$cm$^{-2}$, leading to a total integrated luminosity of 3000 fb$^{-1}$. Due to the high instantaneous luminosity a particle flux of up to $1\times10^{15}$ n$_{\mathrm{eq}}$cm$^{-2}$ is expected in the outer tracker region. To cope with this challenge the existing CMS Outer Tracker has to be replaced by a completely new subdetector system. This Phase-2 tracker will have an increased granularity with $\le 1\%$ occupancy in all regions and less material compared to the current detector. In addition the CMS Phase-2 tracker will contribute to the level-1 trigger with specialized detector modules with on-board transverse momentum discrimination. The Phase-2 Outer Tracker will consist of 5616 PS modules with a macro-pixel and a strip sensor on top of each other, and 7680 2S modules with two strip sensors on top of each other. In the next years standardized production lines for precise module building and testing are going to be installed in all 2S module production centers in the USA, Germany, Belgium, Pakistan, and India. The current plan foresees to integrate PS and 2S modules on tracker substructures starting 2022 and to start integrating the complete Phase-2 tracker in CMS in 2024 for the operation at the High Luminosity LHC.