Top quark couplings in past, present and future colliders
- Autores: Martín Perelló Roselló
- Directores de la Tesis: Marcel Vos (dir. tes.), Gauthier Durieux (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: Hitoshi Yamamoto (presid.), Antonio Pich (secret.), Jenny List (voc.)
- Programa de doctorado: Programa de Doctorado en Física por la Universitat de València (Estudi General)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RODERIC
- Resumen
The Standard Model (SM) is the most complete description of elementary particles and their interactions. It is composed by bosons, integer spin particles which mediate the interactions, and fermions, spin-1/2 particles which constitute matter. However, the SM is still not the final theory. It does not include gravitation as a quantum field theory, it does not offer a clear explanation of what could constitute the Dark Matter and it predicts the neutrinos to be massless. Particle physicists therefore work on different theories Beyond the Standard Model (BSM) to address these problems.
For studying deviations from the SM in top-quark physics we use an effective field theory (EFT) approach. EFTs allow us to parameterize the unknown low-energy physics effects respect to some high energy scale. We describe the top-quark couplings in terms of SM and BSM contributions of dimension-six effective operators.
In a first study, we interpret the charge asymmetry measurement for the process pp → tt at the LHC in terms of four-quark dimension-six operators. These kind of operators have enhanced effects in the boosted regime, so we use differential measurements of the charge asymmetry for high values of the invariant mass of the tt system.
In a second study, we perform a global fit of the EW couplings of the top and bottom quarks. We have a total of 10 effective operators describing the left and right couplings of the top and bottom quark to the Z boson, the charged current Wtb, the EW dipole operators and the top-Yukawa coupling. We constrain these operators with existing data from SLC/LEP and from the Run 2 of the LHC.
Furthermore, we study how these bounds would improve during the remaining programme of the LHC and at a future electron-positron collider. We compare the existing bounds with the bounds that would derive from data collected at s = 250 and s = 500 GeV, at the International Linear Collider (ILC). We show that the bounds improve very strongly with the constraints from the e+e− → tt production process. We also study the impact of adding the two-lepton-two-quark operators to the 10-parameter fit. In this case, we add 7 extra operators and an extra centre-of-mass energy, s = 1 TeV, is needed. We demonstrate that a 17-parameter fit is robust.
