The Phase-1 Upgrade of the CMS Pixel Detector

The innermost tracking device of the CMS experiment is a silicon pixel detector. It has to cope with high particle fluxes and radiation damage, and was built to withstand the LHC design luminosity of 1$\times10^{34}$ cm$^{-2}$s$^{-1}$. This luminosity was already exceeded in 2016 and it is foreseen that it will increase further, potentially reaching two times the design value before 2018. Under such conditions the inefficiencies due to a limited readout bandwidth will increase by as much as 16\% in the innermost layer. To maintain high tracking efficiency, the CMS collaboration has built a new pixel detector that was installed in March 2017. In this paper, the design of this so-called Phase-1 pixel detector is summarised, the production and the qualification of the pixel modules is described and the current status of the project is reported.