Studies of H->bb and the Higgs self-coupling

In 2012 the Higgs boson was discovered in collisions of the Large Hadron Collider at CERN. Nonetheless, the decay of the Higgs boson to bottom quarks, H->bb, has not yet been measured due to the poor signal to background ratio in this channel. Developing methods to extract the small H->bb signal from the large QCD background is critical to determine the coupling of the Higgs to b-quarks. Furthermore, it is also essential to study the Higgs self-coupling using di-boson production. Higgs pair production is directly sensitive to the Higgs trilinear coupling and provides crucial information on the electroweak symmetry breaking mechanism. The di-Higgs production rate in the Standard Model is extremely small, approximately only 40fb at 14 TeV, and therefore the largest Higgs decay mode, H->bb, is used in most of the analyses aiming to study the Higgs self-coupling. These analyses include HH->4 b quarks, HH->2b quarks+2photons. Mr. Ambroz will work on the ATLAS experiment at the LHC. He will first develop new methods to determine the b-tagging efficiency for high transverse momentum jets using data. This is critical as the LHC is now operating at higher center of mass energies. He will then focus on the measurement of H->bb using advanced multivariate methods. He will benefit from the activities that are taking place in the AMVA4NP network, supported by Horizon 2020. This network focuses on the development of new tool for classification and regression problems that are especially important first for finding and then to study in detail H->bb. Mr. Ambroz will study the large QCD background in the bb final state and develop more effective methods to describe this background using data. He will also develop new methods to improve the b-tagging for H->bb as the luminosity of the LHC increases in run 2. The long term goal will be to apply the techniques developed for H->bb also to the study of di-Higgs production in final states that include 4 b-quarks and can be used to test the Higgs self-coupling.