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

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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 \begin{equation}\nonumber 3620.6\pm 1.5 (\text{stat})\pm 0.4 (\text{syst}) \pm 0.3 (\Xi_{c}^{+}) \text{MeV}/\it{c}^{2}, \end{equation} and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be \begin{equation}\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}). \end{equation}

Figures and captions

Dominant Feynman diagram contributing to the decay $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+ $ .

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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.

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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.

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Animated gif made out of all figures.


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.

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Supplementary Material [file]

Supplementary material full pdf

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Fig3.pdf [61 KiB]
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Created on 16 February 2019.Citation count from INSPIRE on 16 February 2019.