The CMS detector at the CERN LHC features a silicon pixel detector as its innermost subdetector. The original CMS pixel detector has been replaced with an upgraded pixel system (CMS Phase-1 pixel detector) in the extended year-end technical stop of the LHC in 2016/2017. The upgraded CMS pixel detector is designed to cope with the higher instantaneous luminosities that have been achieved by the LHC after the upgrades to the accelerator during the first long shutdown in 2013–2014. Compared to the original pixel detector, the upgraded detector has a better tracking performance and lower mass with four barrel layers and three endcap disks on each side to provide hit coverage up to an absolute value of pseudorapidity of 2.5. This paper describes the design and construction of the CMS Phase-1 pixel detector as well as its performance from commissioning to early operation in collision data-taking.
The upgrade of the LHC to the High-Luminosity LHC (HL-LHC) is expected to increase the LHC design luminosity by an order of magnitude. This will require silicon tracking detectors with a significantly higher radiation hardness. The CMS Tracker Collaboration has conducted an irradiation and measurement campaign to identify suitable silicon sensor materials and strip designs for the future outer tracker at the CMS experiment. Based on these results, the collaboration has chosen to use n-in-p type silicon sensors and focus further investigations on the optimization of that sensor type. This paper describes the main measurement results and conclusions that motivated this decision.
The structure of the CMS inner tracking system has been studied using nuclear interactions of hadrons striking its material. Data from proton-proton collisions at a center-of-mass energy of 13 TeV recorded in 2015 at the LHC are used to reconstruct millions of secondary vertices from these nuclear interactions. Precise positions of the beam pipe and the inner tracking system elements, such as the pixel detector support tube, and barrel pixel detector inner shield and support rails, are determined using these vertices. These measurements are important for detector simulations, detector upgrades, and to identify any changes in the positions of inactive elements.
The CMS Inner Tracker, made of silicon pixel modules, will
be entirely replaced prior to the start of the High Luminosity LHC
period. One of the crucial components of the new Inner Tracker
system is the readout chip, being developed by the RD53
Collaboration, and in particular its analogue front-end, which
receives the signal from the sensor and digitizes it. Three
different analogue front-ends (Synchronous, Linear, and
Differential) were designed and implemented in the RD53A
demonstrator chip. A dedicated evaluation program was carried out to
select the most suitable design to build a radiation tolerant pixel
detector able to sustain high particle rates with high efficiency
and a small fraction of spurious pixel hits. The test results showed
that all three analogue front-ends presented strong points, but also
limitations. The Differential front-end demonstrated very low noise,
but the threshold tuning became problematic after
irradiation. Moreover, a saturation in the preamplifier feedback
loop affected the return of the signal to baseline and thus
increased the dead time. The Synchronous front-end showed very good
timing performance, but also higher noise. For the Linear front-end
all of the parameters were within specification, although this
design had the largest time walk. This limitation was addressed and
mitigated in an improved design. The analysis of the advantages and
disadvantages of the three front-ends in the context of the CMS
Inner Tracker operation requirements led to the selection of the
improved design Linear front-end for integration in the final CMS
readout chip.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.