CMS technical developments

Jets are the experimental signatures of quarks and gluons produced in proton-proton collisions. The detailed understanding of their properties is crucial for many physics analyses, and is an important source of systematic uncertainty. Our group is deeply involved in the jet energy calibration in CMS since many years, being responsible for the calibration of the jet energy scale and resolution as measured by the detector.

In the CMS detector, a two-level trigger system is installed to select interesting collision events. The first level trigger (L1) is designed to take a decision synchronously with the 40 MHz bunch-crossing rate. The system is built in custon hardware and has been successfully operated in run-1 and run-2 of CMS data-taking. For the high-luminosity-LHC (HL-LHC) an upgrade of the L1 trigger system is foreseen to provide an even more efficient event selection within the bandwidth constrains in this very challenging environment. In oder to meet the harsh requirements, new algorithms of artificial intelligence (machine learning) are foreseen to be executed on field-programmable-gate-arrays (FPGAs). We are developing the respective algorithms, simulate their performance and test them on our local FPGA hardware, before being installed in the online environment of the CMS L1 trigger in the future.

The identification of jets originating from top quark decays is crucial in many searches for new physics and standard model measurements probing the highest scales. In our group, we perform measurements of the top tagging efficiencies in data and simulation through template fits to the measured jet mass distribution. These measurements are used to derive correction factors, important for a variety of analyses within the CMS Collaboration.

With increasing instantaneous luminosity at the LHC come additional reconstruction challenges. At high luminosity, many collisions occur simultaneously within one proton-proton bunch crossing. The isolation of an interesting collision from the additional "pileup" collisions is needed for effective physics performance. We are developing and improving techniques capable of mitigating the impact of these pileup collisions.

Detector and environmental observables have to be constantly monitored during data taking, to ensure the efficiency and health of the CMS tracking detector. We are developing and improving software to help the detector operators monitoring theses observables and spotting problems early on. We are contributing to analyses investigating the effect of radiation damage on detector observables. These studies help to predict the evolution of these variables, which constitutes important input for the detector operation in upcoming data taking periods.