Thesis

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 2014

• Academic Year:

  2014 /2015

• 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:

  The electromagnetic and weak forces that shaped the Universe we see today are part of a more fundamental electroweak interaction which dominated the early moments after the Big Bang. In the Standard Model theories of Particle Physics, electroweak symmetry breaking which led to the separate interactions is described by the Higgs mechanism. The Higgs boson was discovered by the ATLAS and CMS experiments at CERN’s LHC collider and constitutes experimental evidence for this mechanism. But there is still much that is unknown about electroweak symmetry breaking and the properties of the Higgs boson. The experimental focus has thus moved to the precise measurements of the Higgs boson properties, since they have deep implications on scenarios of New Physics beyond the Standard Model. In particular, measurements of the associated production of a Higgs boson with a top quark pair – which has not yet been observed – are the only way to directly access the top Yukawa coupling between Higgs and top. This is a very important parameter, since the high mass of the top quark implies that it may play a fundamental role in the underlying dynamics of the electroweak symmetry breaking and the stability of the Universe. The proposed project aims at making the first observation of 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 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, and will require LHC data from several years. From this data it will be possible to make a first observation of the ttH process and a determination of the top Yukawa coupling constant. Any deviation of this value from the Standard Model expectation will indicate the presence of New Physics. The student will take part in ATLAS data taking operations and physics analysis activities, with frequent trips to CERN to participate in Control Room shifts and collaboration meetings.