Development of New ATLAS Trigger Algorithms in Search for New Physics at the LHC
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Abstract
To further explore the physics nature, ever higher luminosities will be achieved by the Large Hadron Collider (LHC). With the restart of the LHC in 2022, the ATLAS experiment, and in particular the dedicated trigger system, has to cope with increased event rates. The first level trigger is redesigned taking advantage of the latest Field Programmable Gate Array (FPGA) technology to i.a. exploit higher granularity data from the electromagnetic and hadronic calorimeters. As part of this, a new subsystem called jet Feature EXtractor (jFEX) is added. It is intended to identify particle showers (jets) and to process global energy sums.
In the context of this thesis, new algorithm firmware was developed for the jFEX system. The newly developed trigger algorithms were implemented appropriately on the target FPGA by requiring a maximum processing time of 125 ns, which is well within the available latency budget of 150 ns. Accompanying, the performance of the new trigger algorithms is presented, showing several improvements over the legacy system. Moreover, trigger efficiency studies were carried out targeting events with invisibly decaying Higgs bosons, which are produced in association with hadronically decaying W or Z bosons. With the newly developed algorithm for computing missing transverse energy, the corresponding trigger threshold can be reduced by more than 30 GeV without changing the rate, which in turn forms a basis for a potential gain in sensitivity for events with low missing transverse energy. According to the Standard Model of particle physics, the fraction of Higgs bosons decaying to an invisible final state is rather small, so that an observation of such events would be a direct indication of new physics.