Speaker
Simon Spannagel
(Deutsches Elektronen-Synchrotron (DE))
Description
The CMS silicon pixel detector is the innermost component of the all-silicon tracking system of CMS. While the current pixel detector is designed for and performing well at the current LHC luminosity, it would be subject to severe inefficiencies at increased hit occupancy of the detector.
Based on the strong performance of the LHC accelerator, it is anticipated that peak luminosities of two times the design luminosity of $\mathcal{L} = 2\times10^{34}\,\mathrm{cm^{-2}s^{-1}}$ are likely to be reached before 2018 and perhaps significantly exceeded in the running period until 2022, referred to as Phase I.
Therefore, an upgrade of the CMS pixel detector is planned, including a new readout chip, additional barrel detector layer and end-cap disks for robust tracking performance, and a significantly reduced overall material budget. The new readout chip design comprises additional on-chip buffer cells as well as a high-speed data link and a low-threshold comparator in the pixel cells. With these changes the upgraded pixel detector will be able to sustain the efficiency of the current pixel tracker at the increased requirements imposed by high luminosities and pile-up.
The effects of these design changes on e.g. position resolution and charge collection efficiency have been studied in detail using a precision tracking telescope at the DESY electron test beam facilities. The telescope track resolution of down to $4\,\mathrm{\mu m}$ enables precise studies of tracking efficiency, charge sharing and collection even within single pixel cells of the device under test.
The new CMS pixel detector modules have been found to perform well. The lower pixel-cell charge threshold of about $\sim1.5\mathrm{k}$ electrons allows for a reduced spatial resolution of $\sim6\,\mathrm{\mu m}$. Detailed simulations of sensor charge collection and chip thresholds have been conducted in order to verify the results and show good agreement with the test beam data. Furthermore, chip prototypes have been irradiated up to the anticipated lifetime dose of the CMS pixel detector outer layer of $130\,\mathrm{kGy}$ and were measured to be still $\sim99.8\,\%$ efficient.
This contribution focuses on the improved performance and capabilities of the new pixel readout chip and summarizes results from test beam campaigns and additional measurements conducted in order to assure the functionality of the new chip design with its improved charge threshold, redesigned data transmission and buffering scheme.
Primary author
Simon Spannagel
(Deutsches Elektronen-Synchrotron (DE))
