# First observation of the doubly charmed baryon decay $\Xi_{cc}^{++} \rightarrow \Xi_{c}^{+} \pi^{+}$

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## Abstract

The doubly charmed baryon decay $\Xi_{cc}^{++} \rightarrow \Xi_{c}^{+} \pi^{+}$ 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 $1.7\,\mathrm{fb}^{-1}$, collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of $13\mathrm{\,TeV}$. The $\Xi_{cc}^{++}$ mass is measured to be $$\nonumber 3620.6\pm 1.5 (\text{stat})\pm 0.4 (\text{syst}) \pm 0.3 (\Xi_{c}^{+}) \text{MeV}/\it{c}^{2},$$ and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be $$\nonumber \frac{\mathcal{B} (\Xi_{cc}^{++} \rightarrow \Xi_{c}^{+} \pi^{+}) \times \mathcal{B}(\Xi_{c}^{+} \rightarrow pK^{-}\pi^{+})} {\mathcal{B} (\Xi_{cc}^{++} \rightarrow \Lambda_c^{+} K^{-} \pi^{+} \pi^{+}) \times \mathcal{B}(\Lambda_c^{+} \rightarrow pK^{-}\pi^{+})} = 0.035\pm 0.009 (\text{stat}) \pm 0.003 (\text{syst}).$$

## Figures and captions

 Dominant Feynman diagram contributing to the decay $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+$ . XicPi_[..].pdf [27 KiB] HiDef png [31 KiB] Thumbnail [6 KiB] *.C file Invariant-mass distribution of the $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+$ (left) and $\Xi ^{++}_{ c c } \rightarrow \Lambda ^+_ c K ^- \pi ^+ \pi ^+$ (right) candidates with result of the fit overlaid. The black points represent the data, the dotted (red) line represents the signal contribution, and the dashed (green) line represents the combinational background. Xicc_Fit.pdf [64 KiB] HiDef png [266 KiB] Thumbnail [96 KiB] *.C file LcKpip[..].pdf [73 KiB] HiDef png [286 KiB] Thumbnail [104 KiB] *.C file Measured $\Xi ^{++}_{ c c }$ masses obtained with the decay modes $\Xi ^{++}_{ c c } \rightarrow \Lambda ^+_ c K ^- \pi ^+ \pi ^+$ and $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+$ , and the combined result. The darker green band represents the statistical uncertainty on the combination, and the lighter green band represents the total uncertainty on the combination. Mass_2[..].pdf [61 KiB] HiDef png [76 KiB] Thumbnail [25 KiB] *.C file Animated gif made out of all figures. PAPER-2018-026.gif Thumbnail

## Tables and captions

 Systematic uncertainties on the measurement of the $\Xi ^{++}_{ c c }$ mass and of the ratio of branching fractions $\mathcal R(\mathcal{B} )$ between the $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+$ and the $\Xi ^{++}_{ c c } \rightarrow \Lambda ^+_ c K ^- \pi ^+ \pi ^+$ decay modes. Table_1.pdf [39 KiB] HiDef png [83 KiB] Thumbnail [13 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf supple[..].pdf [121 KiB] Fig3.pdf [61 KiB] HiDef png [76 KiB] Thumbnail [25 KiB] *C file

Created on 16 February 2019.Citation count from INSPIRE on 16 February 2019.