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| Home > In process > Search for Long-Lived Axion-Like Particles in Events with a Top-Antitop Quark Pair and aDisplaced Dimuon using Data Collected with the CMS Detector at √s = 13 TeV and √s = 13.6 TeV |
| Home > In process > Search for Long-Lived Axion-Like Particles in Events with a Top-Antitop Quark Pair and aDisplaced Dimuon using Data Collected with the CMS Detector at √s = 13 TeV and √s = 13.6 TeV |
| Dissertation / PhD Thesis | PUBDB-2026-03502 |
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2026
Abstract: This thesis presents a search for long-lived axion-like particles (ALPs) produced in association with a topantitopquark pair and decaying to a displaced dimuon, using proton-proton collision data recorded by theCompact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC), at √s = 13 TeV and√s = 13.6 TeV, corresponding to integrated luminosities of 138 and 62 fb−1, respectively. A top-philicALP scenario is considered, in which the ALP couples predominantly to top quarks and the effectivecouplings governing its decay are loop-suppressed, allowing the ALP to be long-lived. A muon from theassociated top-antitop quark pair is used to trigger events largely independently of the ALP parameterspace, allowing access to low ALP masses down to the dimuon threshold. The additional event selectioncriteria on the top final states also help reduce background from Standard Model (SM) processes. As partof this thesis, a phenomenological study established the discovery potential of this signature at the LHCand the High Luminosity LHC (HL-LHC), motivating the search performed with the CMS detector. Thetop-antitop quark pair decay mode to a muon and jets is targeted, requiring one prompt muon from thetop quark decay and two muons forming a displaced dimuon vertex. Three dimuon categories are studied,defined by their muon reconstruction method as PAT-PAT, PAT-DSA, and DSA-DSA. The PAT-PATand DSA-DSA categories are used in the final statistical interpretation. These dimuon categories areoptimized separately to achieve sensitivity across a wide range of dimuon displacements. The predictedbackground is estimated using a data-driven ABCD method. No significant excess is observed in data, andobserved and expected 95% confidence level upper limits are set on the signal production cross section.For a benchmark top-philic ALP model, ALP masses between 0.35 and 2.4 GeV are excluded by both theobserved and expected limits for a proper decay length of 10 nm, extending the probed ALP parameterspace by several orders of magnitude in proper decay length beyond previous searches for prompt ALPdecays in top-antitop quark pair events. This thesis presents the first search for this signature at theLHC.
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