Performance verification of the CMS Phase-1 Upgrade Pixel detector

TL;DR

This paper reports on the performance verification and initial commissioning results of the upgraded CMS Phase-1 Pixel detector, designed to operate efficiently at higher luminosities and improve tracking accuracy in the LHC environment.

Contribution

It presents the first performance evaluation of the new CMS Phase-1 Pixel detector, highlighting improvements and challenges during initial data taking at high luminosity.

Findings

High hit reconstruction efficiency maintained at high occupancy

Successful operation at increased luminosity levels

Enhanced tracking performance with additional inner layer

Abstract

The CMS tracker consists of two tracking systems utilizing semiconductor technology: the inner pixel and the outer strip detectors. The tracker detectors occupy the volume around the beam interaction region between 3 cm and 110 cm in radius and up to 280 cm along the beam axis. The pixel detector consists of 124 million pixels, corresponding to about 2 m$^{2}$ total area. It plays a vital role in the seeding of the track reconstruction algorithms and in the reconstruction of primary interactions and secondary decay vertices. It is surrounded by the strip tracker with 10 million read-out channels, corresponding to 200 m$^{2}$ total area. The tracker is operated in a high-occupancy and high-radiation environment established by particle collisions in the LHC. The performance of the silicon strip detector continues to be of high quality. The pixel detector that has been used in Run 1 and in the first half of Run 2 was, however, replaced with the so-called Phase-1 Upgrade detector. The new system is better suited to match the increased instantaneous luminosity the LHC would reach before 2023. It was built to operate at an instantaneous luminosity of around 2$\times$10$^{34}$cm$^{-2}$s$^{-1}$. The detector's new layout has an additional inner layer with respect to the previous one; it allows for more efficient tracking with smaller fake rate at higher event pile-up. The paper focuses on the first results obtained during the commissioning of the new detector. It also includes challenges faced during the first data taking to reach the optimal measurement efficiency. Details will be given on the performance at high occupancy with respect to observables such as data-rate, hit reconstruction efficiency, and resolution.