# First Observation of the Doubly Charmed Baryon Decay ${\Xi }_{cc}^{++}\to {\Xi }_{c}^{+}{\pi }^{+}$

18 October 2018

Abstract: The doubly charmed baryon decay ${\Xi }_{cc}^{++}\to {\Xi }_{c}^{+}{\pi }^{+}$ is observed for the first time, with a statistical significance of $5.9\sigma$, confirming a recent observation of the baryon in the ${\Lambda }_{c}^{+}{K}^{-}{\pi }^{+}{\pi }^{+}$ final state. The data sample used corresponds to an integrated luminosity of $1.7\text{}\text{}{\mathrm{fb}}^{-1}$, collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of 13 TeV. The ${\Xi }_{cc}^{++}$ mass is measured to be $3620.6±1.5\left(\mathrm{stat}\right)±0.4\left(\mathrm{syst}\right)±0.3\left({\Xi }_{c}^{+}\right)\text{}\text{}\mathrm{MeV}/{c}^{2}$ and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be $\left[B\left({\Xi }_{cc}^{++}\to {\Xi }_{c}^{+}{\pi }^{+}\right)×B\left({\Xi }_{c}^{+}\to p{K}^{-}{\pi }^{+}\right)\right]/\left[B\left({\Xi }_{cc}^{++}\to \phantom{\rule{0ex}{0ex}}{\Lambda }_{c}^{+}{K}^{-}{\pi }^{+}{\pi }^{+}\right)×B\left({\Lambda }_{c}^{+}\to p{K}^{-}{\pi }^{+}\right)\right]=0.035±0.009\left(\mathrm{stat}\right)±0.003\left(\mathrm{syst}\right)$.

Published in: Physical Review Letters 121 (2018)