Observation of the doubly-charmed-baryon decay $ {\Xi}_{cc}^{++}\to {\Xi}_c^0{\pi}^{+}{\pi}^{+} $

A search for the doubly-charmed-baryon decay ${\Xi}_{cc}^{++}\to {\Xi}_c^0{\pi}^{+}{\pi}^{+}$ is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 5 . 4 fb − 1 . A significant structure consistent with the ${\Xi}_{cc}^{++}$ baryon is observed in the ${\Xi}_c^0{\pi}^{+}{\pi}^{+}$ invariant-mass spectrum. Using the ${\Xi}_{cc}^{++}\to {\Lambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+}$ decay as the normalisation channel, the branching fraction ratio, $\frac{\mathcal{B}\left({\Xi}_{cc}^{++}\to {\Xi}_c^0{\pi}^{+}{\pi}^{+}\right)}{\mathcal{B}\left({\Xi}_{cc}^{++}\to {\Lambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+}\right)}$ , is measured to be 1 . 37 ± 0 . 18 (stat) ± 0 . 09 (syst) ± 0 . 35 (ext). This measurement provides critical input for testing QCD factorisation methods in the weak decays of doubly-heavy baryons, particularly in quantifying nonperturbative effects such as final-state interactions and resonance contributions to the hadronisation process.