Evaluation of irradiated barrel detector modules for the upgrade of the CMS pixel detector

The instantaneous luminosity of the Large Hadron Collider (LHC) is being increased in several steps over the next 10 years to maximize its discovery potential for new physics. However, at a luminosity of twice the design luminosity of the LHC of 1×10³⁴ cm^-2s^-1, the performance of the current CMS pixel detector is degraded by substantial deadtime incurred by the readout chip (ROC). To make full use of the proton-proton collisions being provided by the LHC, CMS will replace its pixel detector in 2016/17 by a new four-layer detector. The new readout chip used in the barrel detector will have increased buffering capabilities to minimize deadtime, and digital readout protocol to increase the readout speed. CMS recently received a prototype version of the new digital ROC. Prototype detector modules comprising sensors and the new readout chips were assembled and irradiated with protons at the CERN PS, and readout chips without sensors have been irradiated with protons at the Karlsruhe Zyklotron to test their performance under LHC conditions. The modules are being evaluated in an electron test beam at DESY, and the ROCs are evaluated in lab measurements. Key chip parameters and results of the absolute energy calibration are compared as a function of particle fluence.