Search for associated Higgs boson production with a top quark pair and measurement of the top Yukawa coupling using LHC run-II data from ATLAS


  • Call:

    IDPASC Portugal - PHD Programme 2017

  • Academic Year:

    2017 / 2018

  • Domain:

    Experimental Particle Physics

  • Supervisor:

    Ricardo Gonçalo

  • Co-Supervisor:

    Patricia Conde Muino

  • Institution:

    Faculdade de Ciências - Universidade de Lisboa

  • Host Institution:

    Laboratório de Instrumentação e Física Experimental de Partículas

  • Abstract:

    Since the discovery of the Higgs boson at the ATLAS and CMS experiments of CERN’s LHC collider, the experimental focus has moved to the precise measurements of the Higgs boson properties. To do this, however, it is crucial to observe and study the production of the new boson in association with a pair of top quarks, ttH, which has not yet been achieved and will require data to be collected in the next few years. This production channel provides the only way to directly measure the top Yukawa coupling between Higgs and top. This is the largest coupling of the Higgs boson to matter particles in the Standard Model theories of particle physics, and there are reasons to believe it may show the way to the elusive physics beyond the current theories. The proposed project aims at observing the associated Higgs boson production with a top quark pair, ttH, using the ATLAS experiment at the LHC collider. It will imply the analysis of proton-proton collisions recorded at a centre of mass of 13 TeV during the LHC run II, from 2015 to 2018, using advanced computing and simulation of the complex ATLAS detector. This is a challenging analysis at the cutting edge of Particle Physics research. To make it possible, we propose to use new analysis techniques being developed at LIP, which involves the use of angular correlations between particles in the event and arise due to the spin of the Higgs boson. These techniques improve the separation between the Higgs signal and the dominant irreducible background. These analysis techniques also have the potential to be applied to other analyses and the student will contribute to their development. From this analysis, it will be possible to make an observation of the Higgs boson in ttH production, and to determine the top Yukawa coupling. Any deviation of this coupling from the Standard Model expectation will indicate the presence of new physics and will be a major discovery. The student will be integrated in the Portuguese ATLAS team and will take part in ATLAS data taking operations and physics analysis activities. Frequent trips to CERN may be required to participate in Control Room shifts and collaboration meetings.