New observables for resonant and non-resonant new physics searches at colliders
(2026)
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- Abstract
- (en) The discovery of the Higgs boson cemented the form of the Standard Model of particle physics (SM) as we know it and observations have so far confirmed SM predictions about the couplings of the Higgs with other particles. If the particle physics community used to face too few models other than the Higgs before its observation to explain the origin of the particle masses, too many beyond-the-Standard-Model (BSM) models can be explored to overcome the remaining shortcomings of the SM. As a result, generic models present a useful intermediary step to point towards the potential extension of the SM probing multiple Ultraviolet (UV) models simultaneously. In this work, two examples of generic models are investigated. Off-shell effects of potential heavy new particles are provided in the Stan- dard Model Effective Field Theory (SMEFT) through higher dimensional op- erators. In particular, charge-parity (CP ) symmetry violating contributions from Wilson coefficients are ranked by using several U (1) global flavour sym- metries on CP -odd operators of the Warsaw basis. Asymmetries of simple observables, such as triple products, are proven to be more sensitive to the SMEFT operators compared to the cross-section and more efficient than most of the usual observables used in experiments. We use the dileptonic decays of the diboson W ± Z and W ± γ processes to demonstrate the efficiency of these observables compared to the theoretical and measurable optimal observables. On-shell effects of two heavy scalars are independently searched for in four-top production. These new scalars are singlet and octet of SUC (3) that couple to the top quark. The signal consists of the associated production of a scalar with a top quark pair and of pair production in the case of the octet where the fully hadronic, the leptonic and the same-sign-lepton dileptonic decay channels are considered. The decays of the massive scalars generate boosted top-quark pairs producing event topologies that are suppressed in the SM. The processes are generated at next-to-leading order (NLO) in quantum chromodynamics (QCD) with a careful renormalisation procedure and the cor- rect selection of loop diagrams. Using improvements in top-jet tagging tech- niques and in the main background simulation as well as a new technique to select the events, a new particle search is performed to constrain the respec- tive mass and coupling to top quarks of new resonances. The analysis yields improved limits by up to an order of magnitude compared to previous analyses.
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Touchèque, J. (2026). New observables for resonant and non-resonant new physics searches at colliders. https://hdl.handle.net/2078.5/280709