XXXVI Reunión Bienal de la Real Sociedad Española de Física

Challenging the Standard Model with top quarks interactions

17 jul. 2017 17:15

30m

Aula Química Técnica (Facultad de Química (USC))

Oral parallel contribution Particle and Theoretical Physics Particle and Theoretical Physics I

Descripción

The elementary particles, their properties and their interactions are described by the Standard Model (SM), which is the theoretical framework for the study of the strong interactions of quarks and gluons and the unified electroweak force by means of a modelling framework based on local gauge invariance. The SM is very successful in accounting for most of the observed phenomena at the microscopic frontier of physics, verified and tested in many experiments in the last decades, also including the discovery of the Higgs boson by the ATLAS and CMS experiments at the LHC facility at CERN laboratory in 2012. However, new theories beyond the SM are still needed to explain many pending questions in physics: the matter-antimatter asymmetry, the pattern of flavour mixings and fermion masses, the nature of dark matter or the accelerated expansion of the Universe. The SM accommodates the measured masses, but it does not explain the vastly different mass scales spanned by the known particles. The dynamics of flavour and the origin of CP violation are also related to the mass generation, but still not fully understood. The SM should be either extended or replaced by a more general modelling framework, but experimental evidences are needed to point in which direction the SM should be modified. The top quark is a very sensitive probe of the electroweak symmetry breaking, since it is the heaviest fundamental particle with the SM framework.Its large mass makes the top very different from all other quarks, with a Yukawa coupling to the Higgs boson close to unity. For these reasons the top quark and the Higgs boson play very special roles in the SM and in many extensions thereof. An accurate knowledge of their properties (mass, couplings, production cross section, decay branching ratios) can bring key information on fundamental interactions at the electroweak breaking scale and beyond. Some of the top quark couplings were investigated at the Tevatron, while others, such as the coupling of the top quark to the Z or the Higgs boson are becoming accessible only with the high-statistics top quark sample at the LHC. This contribution provides a comprehensive overview of the latest ATLAS results for tt+Z/W and tt+H processes.