Observation of the doubly-charmed-baryon decay ${\hat{I}ž}_{cc}^{++}\to {\hat{I}ž}_c^0\ddot{I}{€}^{+}\ddot{I}{€}^{+}$

Abstract

A search for the doubly-charmed-baryon decay ${\hat{I}ž}_{cc}^{++}\to {\hat{I}ž}_c^0\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\text{TeV}$ and corresponding to an integrated luminosity of $5.4{\text{fb}}^{-1}$. A significant structure consistent with the ${\hat{I}ž}_{cc}^{++}$ baryon is observed in the ${\hat{I}ž}_c^0\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ invariant-mass spectrum. Using the ${\hat{I}ž}_{cc}^{++}\to {\hat{I}›}_c^{+}{K}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+}$ decay as the normalisation channel, the branching fraction ratio, $\frac{\mathcal{B}({\hat{I}ž}_{cc}^{++}\to {\hat{I}ž}_c^0\ddot{I}{€}^{+}\ddot{I}{€}^{+})}{\mathcal{B}({\hat{I}ž}_{cc}^{++}\to {\hat{I}›}_c^{+}{K}^{-}\ddot{I}{€}^{+}\ddot{I}{€}^{+})}$, is measured to be $1.37\pm 0.18\text{(stat)}\pm 0.09\text{(syst)}\pm 0.35\text{(ext)}$. 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.

21 pages, 3 figures All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1615/ (LHCb public pages)."