Abstract
The instantaneous luminosity of the Large Hadron Collider will increase to up to 2x1034\\;cm−2s−1 by 2023. In order to cope with such luminosities, the pixel detector of the CMS experiment has been replaced in January 2017. The upgraded detector features four sensitive layers in the barrel part. A designated readout chip (PROC600V2) is used for layer 1, which is located only 3 cm from the interaction point and therefore has to handle large particle fluxes. An irradiation campaign has been performed with PROC600V2 to verify its radiation tolerance up to the maximum expected dose for 2017 of 0.2 MGy which proved that no performance loss is expected at the tested doses. Modules for layer 1 have been built with PROC600V2 for the detector production. The quality of every inserted module was assessed in a number of tests, some of which were performed using X-radiation. The characteristics of the modules used in the detector as well as the main failure modes will be presented. It will be shown that the installed modules have an efficiency of over 98% at the maximum expected particle hit rate in CMS.
Highlights
A designated readout chip (PROC600V2) is used for layer 1, which is closest to the interaction point and has to handle larger particle fluxes
A similar study has been performed with PROC600, the first version of the readout chip and with PSIdigV2.1respin, the ROC used for layers 2 to 4, to doses of up to 4.2 MGy, and no significant defects originating from irradiation were observed [3, 5]
The quality of the modules installed in layer 1 of the Phase 1 upgrade of the CMS pixel detector has been assessed in multiple ways
Summary
The readout chip used for the upgraded pixel detector was designed by the PSI High Energy Physics group. It is possible to inject test pulses in the readout chip which follow the same readout chain than hits created by particles This functionality simplifies the testing of the ROCs’ properties [2]. In order to face this challenge, it features a new readout mechanism, reading out clusters of four pixels simultaneously instead of single pixels as is the case for the chip used in the outer layers of the detector. This increases the readout speed by a factor 2.4 at the maximum expected rate of ∼600 MHz/cm, where on average 1.2 clusters with a size of 1.95 pixels are created per double column. More details about the design of PROC600 can be found in [3]
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