Public Thesis defense - IRMP


30 septembre 2022



Auditoire CYCL01, Chemin du Cyclotron, 2 - will also take place in video conference

Top quark interactions in the standard model effective field theory by Hesham EL FAHAM

Pour l’obtention du grade de Docteur en sciences

Over the last decade, the enormous amount of data gathered by the Large Hadron Collider (LHC) has put the Standard Model (SM) under severe testing, proving it the most successful theory in particle physics. Despite such success, the SM is an inherently incomplete theory. The current challenges facing the SM have led to the proposals that new physics must exist. This new physics beyond the SM may not be necessarily evident in the resonant production of new particles at the LHC. Therefore, the SM effective field theory approach (SMEFT) can be used as a framework to parameterise possible deviations from the SM due to the presence of such new states that otherwise can not be probed directly with the current reach of our colliders. One of many possible probes of new physics is top quark interactions. The motivation behind the vigorous effort put into probing top quark processes is its high mass and strong coupling to the Higgs boson. This thesis presents three SMEFT studies of different top quark processes at hadron colliders.

Single top quark production associated with a WZ-bosons pair at next-to-leading-order (NLO) in QCD is non-trivial due to its overlap with other resonant processes at leading-order (LO). In the first study of the thesis, we employed diagram-removal methods to suppress the resonant overlap, and therefore, define tWZ at NLO in a suitably defined phase-space region in which SMEFT predictions can be reliably obtained. This study will allow the inclusion of the tWZ data in future global LHC studies.

In the second study, we investigated the four top quark production considering all possible QCD and EW-induced amplitudes for all the relevant dimension-six SMEFT operators. We show that formally subleading terms give rise to significant cross-section contributions, providing sensitivity to a broader class of operators. Inclusive and differential predictions for the LHC and the FCC-hh were obtained. Furthermore, we carried projection studies by which we set limits on the values of the operators’ coefficients at different hadron collider setups.

Finally, the thesis presents the measurement of top-anti-top quark pair production associated with a Higgs boson in the multi-lepton final states by the CMS experiment. We examined the possibility of reconstructing the differential top-Higgs system with the aim of interpreting the measurement in the context of SMEFT. We assessed the reconstruction quality in such attempts, and quantified the associated inefficiencies. The differential study delivers constraints on the relevant effective coefficients.

Jury members :

  • Dr. Andrea Giammanco (UCLouvain), supervisor
  • Prof. Jorgen D’Hondt (VUB), supervisor
  • Prof. Fabio Maltoni (UCLouvain), chairperson
  • Prof. Alberto Mariotti (VUB), secretary
  • Prof. Céline Degrande (UCLouvain)
  • Prof. Christoph Englert (Univ. of Glasgow, Scotland)
  • Dr. Denise Muller (VUB)
  • Dr. Eleni Vryonidou (Univ. of Manchester, UK)

Pay attention :

The public defense of Hesham El Faham scheduled for Friday 30 September at 03:00 p.m. will also take place in the form of a video conference

Meeting ID: 833 9899 0528
Passcode: 499754

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