A version of the article arXiv:2510.19080v2 [hep-ex] (https://arxiv.org/abs/2510.19080). Comments: Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at https://cms-results.web.cern.ch/cms-results/public-results/publications/TOP-24-009/ (CMS Public Pages). Report number: CMS-TOP-24-009, CERN-EP-2025-205. Journal reference: Phys. Rev. Lett. 136 (2026) 081802. Submission history: From: The CMS Collaboration: [v1] Tue, 21 Oct 2025 21:11:33 UTC (480 KB); [v2] Mon, 2 Mar 2026 13:49:20 UTC (484 KB).The first observation of single top quark production in association with a and a boson in proton-proton collisions is reported. The analysis uses data at center-of-mass energies of 13 and 13.6 TeV recorded with the CMS detector at the CERN LHC, corresponding to a total integrated luminosity of 200 fb⁻¹. Events with three or four charged leptons, which can be electrons or muons, are selected. Advanced machine-learning algorithms and improved reconstruction methods, compared to an earlier analysis, result in an unprecedented sensitivity to production. The measured cross sections for production are 248 ± 52 fb and 242 ± 77 fb for √ = 13 and 13.6 TeV, respectively. The signal is established with a statistical significance of 5.8 standard deviations, with 3.5 expected, compared to the background-only hypothesis.SCOAP³
