Abstract
The decay \( B_c^{+} \) → J/ψK + K − π + is observed for the first time, using protonproton collisions collected with the LHCb detector corresponding to an integrated luminosity of 3 fb−1. A signal yield of 78 ± 14 decays is reported with a significance of 6.2 standard deviations. The ratio of the branching fraction of \( B_c^{+} \) → J/ψK + K − π + decays to that of \( B_c^{+} \) → J/ψπ + decays is measured to be 0.53 ± 0.10 ± 0.05, where the first uncertainty is statistical and the second is systematic.

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References
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