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

Abstract

A search for the doubly-charmed-baryon decay ${\it \Xi}_{cc}^{++}\to{\it \Xi}_{c}^{0}\pi^{+}\pi^{+}$ is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\text{TeV}$ and corresponding to an integrated luminosity of $5.4\text{fb}^{-1}$. A significant structure consistent with the ${\it \Xi}_{cc}^{++}$ baryon is observed in the ${\it \Xi}_{c}^{0} \pi^{+}\pi^{+}$ invariant-mass spectrum. Using the ${\it \Xi}_{cc}^{++}\to{\it \Lambda}_{c}^{+}K^{-}\pi^{+}\pi^{+}$ decay as the normalisation channel, the branching fraction ratio, $\frac{{\cal B}({\it \Xi}_{cc}^{++} \to {\it \Xi}_{c}^{0}\pi^{+}\pi^{+})} {{\cal B}({\it \Xi}_{cc}^{++}\to{\it \Lambda}_{c}^{+} K^{-}\pi^{+}\pi^{+})}$, 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.