Test Beam Performance Measurements for the Phase I Upgrade of the CMS Pixel Detector

A new pixel detector for the CMS experiment is being built, owing to the instantaneous luminosities anticipated for the Phase I Upgrade of the LHC. The new CMS pixel detector provides four-hit tracking while featuring a reduced material budget as well as new cooling and powering schemes. A new front-end readout chip mitigates buffering and bandwidth limitations, and comprises a low-threshold comparator. These upgrades allow the new pixel detector to sustain and improve the efficiency of the current pixel tracker at the increased requirements imposed by high luminosities and pile-up. In this paper, comprehensive test beam studies are presented which have been conducted to verify the design and to quantify the performance of the new detector assemblies in terms of tracking efficiency and spatial resolution. Under optimal conditions, the tracking efficiency has been determined to be ($99.95 \pm 0.05$) \%, while the intrinsic spatial resolution has been measured to be ($4.80 \pm 0.25$) $\mu$m and ($7.99 \pm 0.21$) $\mu$m along the $100\,\mu$m and $150\,\mu$m pixel pitch, respectively. The findings are compared to detailed Monte Carlo simulations of the pixel detector and a good agreement is found.