Higgs boson coupling with the Top quark
The ATLAS collaboration has built one of the four major experiments at the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN). It has been critical in the detection and characterisation of the Higgs boson, the particle responsible for manifesting mass in the universe. Funded by the EU, the ATLASTTH (Observation of the Higgs production mode in the ttH channel at ATLAS) project focused on improving understanding of the Higgs boson by measuring one of its properties, coupling with the Top quark. There is great interest in this measurement because the Top quark has a very large mass; hence, the strength of the coupling is high, higher than any other coupling. Furthermore, this coupling has a special role in many theories that extend the SM, currently the best theory we have to describe the composition of the universe. In order to discriminate between the value predicted from the SM and those predicted by other theories, a precise measurement is required. During the first period of ATLAS data collection the data collected were insufficient to measure the coupling, but an upper limit to the value was set. After a three-year period in which the LHC and the experiments underwent major improvements, ATLAS started its second period of data collection, which continues. At minimum, the new data will provide an improved upper limit and may provide the first estimate. The project contributed to the experiment by developing software required for operations during the second period of data collection. The new software is responsible for the handling of the online trigger database. In addition to adding all the required new functionalities, it has significantly improved the performance of the application and clarified the code structure to improve the maintainability of the application. Another contribution was publication of the measurement of the Top pair differential cross-section, using the data collected in the first data collection period. Having performed analyses using the Top group software framework and experience in the trigger group, the project lead was invited to join the Top group management with the role of trigger contact person, coordinating between groups proposing new trigger criteria, which determine which events are recorded.
Keywords
Higgs boson, Top quark, standard model, particle physics, ATLASTTH
