Observation of the doubly charmed baryon decay Ξ_cc⁺⁺→Ξ_c^′+π⁺

The Ξ_cc⁺⁺→Ξ_c^′+π⁺ decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^−1. The Ξ_cc⁺⁺→Ξ_c^′+π⁺ decay is reconstructed partially, where the photon from the Ξ_c^′+→Ξ_c⁺γ decay is not reconstructed and the pK⁻π⁺ final state of the Ξ_c⁺ baryon is employed. The Ξ_cc⁺⁺→Ξ_c^′+π⁺ branching fraction relative to that of the  Ξ_cc⁺⁺→Ξ_c⁺π⁺ decay is measured to be 1.41 ± 0.17 ± 0.10, where the first uncertainty is statistical and the second systematic.