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Experimental Particle and Astro-Particle Physics Seminar
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Europe/Zurich
Description
Abstract:
The Large Hadron Collider (LHC) at CERN is the highest energy collider ever built. The LHC therefore probes smaller distances and larger energies than ever accessible before. The top quark, discovered 30 years ago at the Fermilab proton-antiproton collider Tevatron, is the most recent member of the known families of quarks. The LHC is a top quark factory providing high-precision access to top quark physics.
In this seminar, I will present a search for resonances in top quark pair (ttbar) production, based on proton-proton collision data collected by the CMS experiment between 2016 and 2018 at the LHC at a center-of-mass energy of √s= 13 TeV. The analysis explores the invariant mass of the ttbar quark system and two angular observables that provide direct access to the correlation of top quark and antiquark spins. A significant excess of events is observed near the kinematic ttbar threshold compared to the nonresonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD). The observed enhancement is consistent with the production of a color-singlet pseudoscalar 1S[1]0 quasi-bound toponium state, as predicted by nonrelativistic quantum chromodynamics. However, I will also discuss alternative hypotheses to interpret the excess, for example, through elementary scalar or pseudoscalar production.