CMS Phase-1 Pixel Detector: Operational Experience, Performance and Lessons Learned

The CMS Phase-1 pixel detector was designed to cope with an instantaneous luminosity of $2\times$10$^{34}$ cm$^{-2}$s$^{-1}$ at 25\,ns bunch spacing with very small efficiency loss. The Phase-1 pixel detector features four barrel layers and three disks per side, with in total 124 Million pixels, while the original CMS pixel detector had one layer and disk less in the barrel and endcap respectively, and only half the number of channels. DC-DC converters were introduced to deliver more power to the detector without the need of replacing the cable plant. CO$_{2}$ based cooling was implemented and carbon-based structures were constructed to reduce the material in the tracking volume. The data acquisition system was upgraded to accept higher event rates and a new, digital data format from the detector front-ends. The detector was installed in early 2017 and has been successfully operated since. The LHC is going through a planned long shutdown period during 2019-2020. The pixel detector was extracted in early 2019 after the end of Run~2 data taking and has been kept cold to protect the silicon sensors. The innermost barrel layer will be replaced during this shutdown period and will feature improved ASICs and circuit boards to rectify issues discovered during data taking. This paper focuses on the operational experience of the detector in 2018, highlighting the detector performance and addressing the lessons learned. The current status of the detector and the refurbishment plan will also be discussed.