Ablikim, M.Achasov, M.N.Adlarson, P.Ai, X.C.Aliberti, R.Amoroso, A.Çetin, Serkant Ali2024-05-192024-05-1920242470-0010https://doi.org/10.1103/PhysRevD.109.L071103https://hdl.handle.net/20.500.12713/4526The singly Cabibbo-suppressed decay ?c+??-K+?+ is observed for the first time with a statistical significance of 5.4? by using 4.5 fb-1 of e+e- collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. The absolute branching fraction of ?c+??-K+?+ is measured to be (3.8±1.2stat±0.2syst)×10-4 in a model-independent approach. This is the first observation of a Cabibbo-suppressed ?c+ decay involving ?- in the final state. The ratio of branching fractions between ?c+??-K+?+ and the Cabibbo-favored decay ?c+??-?+?+ is observed to be (0.4±0.1)sc2, where scsin?c=0.2248 with ?c the Cabibbo mixing angle. © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.eninfo:eu-repo/semantics/closedAccessArticle10972-s2.0-8519216794210.1103/PhysRevD.109.L071103Q1