  The CMS detector at the CERN LHC features a silicon pixel detector as its
innermost subdetector. The original CMS pixel detector has been replaced with
an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end
technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is
designed to cope with the higher instantaneous luminosities that have been
achieved by the LHC after the upgrades to the accelerator during the first long
shutdown in 2013-2014. Compared to the original pixel detector, the upgraded
detector has a better tracking performance and lower mass with four barrel
layers and three endcap disks on each side to provide hit coverage up to an
absolute value of pseudorapidity of 2.5. This paper describes the design and
construction of the CMS Phase-1 pixel detector as well as its performance from
commissioning to early operation in collision data-taking.
