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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 \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 ^+ $ .

XicPi_[..].pdf [27 KiB]
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XicPi_Feynman.pdf

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]
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Xicc_Fit.pdf
LcKpip[..].pdf [73 KiB]
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LcKpipi_Fit.pdf

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]
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Mass_2016_results.pdf

Animated gif made out of all figures.

PAPER-2018-026.gif
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thumbnail_PAPER-2018-026.gif

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]
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tex code
Table_1.pdf

Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [121 KiB]
supplementary.pdf
Fig3.pdf [61 KiB]
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Fig3.pdf

Created on 17 December 2018.Citation count from INSPIRE on 18 December 2018.