AxiTop: Hunting for axion-like particles with top quarks at the high-energy frontier

• Grant number: 24/08628-3
• Support Opportunities: Regular Research Grants
• Start date: January 01, 2025
• End date: December 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Physics - Elementary Particle Physics and Fields
• Principal Investigator: Thiago Rafael Fernandez Perez Tomei
• Grantee: Thiago Rafael Fernandez Perez Tomei
• Principal researcher abroad: Didar Dobur
• Institution abroad: Ghent University (UGent), Belgium
• Principal researcher abroad: Kirill Skovpen
• Institution abroad: Ghent University (UGent), Belgium
• Host Institution: Núcleo de Computação Científica (NCC). Universidade Estadual Paulista (UNESP). Campus de São Paulo. São Paulo , SP, Brazil

Abstract

Understanding Nature at both the smallest and the largest scales in our Universe has culminated in celebrated theories which are among the most predictive and tested ever. Diving into the subatomic world, our understanding of the fundamental building blocks of ordinary matter and their interactions is synthesised in the standard model (SM) of elementary particles. The discovery of the Higgs boson at the Large Hadron Collider (LHC) at CERN, after half a century of experimental effort, was the triumph of the SM and led to the Nobel Prize in physics in 2013. Since this discovery, the CMS and ATLAS experiments at the LHC made tremendous leap forward in measuring the properties of the Higgs boson (i.e. its mass with better than 0.1% precision) as well as precise measurements on other fronts, rigorously testing the predictions of the Standard Model. In spite of the tremendous success of this fundamental theory in describing the the experimental data over the past decades, a number of unanswered questions still haunt us. One of those questions is what comprises 85% of the matter content of the Universe, an unknown component dubbed dark matter (DM). Its gravitational effects at large scales are overwhelmingly established through both astronomical and cosmological observables: the angular velocities of stars in galaxies, the Bullet Cluster of galaxies, the Cosmic Background Radiation and the general large-scale structure of the universe. Deciphering the nature of DM is undoubtedly one of the main goals for the field of high-energy physics. Hundreds of experiments worldwide, from table-top to the largest experiments in existence, try to cast light on this compelling conundrum and more than a thousand peer-reviewed articles featuring "dark matter" in the title are published each year.The unprecedented proton-proton collision energy, the large data volumes reached by the LHC and the CMS detector with supreme particle detection capabilities provide a unique setting for discovering the particle constituting the dark matter. Since the beginning of the LHC, the promoters of this proposal play leading roles at forefront of various dark matter searches within the CMS experiment. With this proposal, AxiTop, they embark on a brand-new data analysis to search and discover axion-like dark matter particle. The hypothetical axion particle was first proposed to address the famous strong-CP problem in Quantum Chromodynamics. Since then, such pseudo-scalar particles, dubbed axion-like-particles (ALPs), have been incorporated in various well motivated theoretical models that extend the SM, and have been sought for in vastly different experiments. The mass of ALPs and their interaction strength with the SM particles are generally free parameters, and depending on these parameters ALPs can either constitute a viable candidate for dark matter or a portal to a more extended dark sector.During Run 2 of the LHC, CMS has collected approximately 137 fb-1 of pp collision data at a centre-of-mass energy sqrt(s) = 13 TeV. Those data are still undergoing analysis, but preliminary results are regularly being published. Preliminary results on searches for BSM physics, in particular, show no significant deviations from the standard model predictions. In view of this situation, it beckons that the set of experimental signatures to be searched for in the LHC data is enlarged as much as possible. An ongoing effort within CMS is to widen the scope of searches for long-lived particles (LLPs), with a large variety of signatures in that category. This avenue of study allows to once again search for the usual BSM phenomena - resonances and invisible particles, including dark matter candidates - in configurations that would not be covered in previous analyses. The ALP may be long-lived for some values of its mass and interaction strength. (AU)