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Observation of the doubly Cabibbo-suppressed decay $\Xi_{c}^{+}\to p\phi$

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Abstract

The doubly Cabibbo-suppressed decay $\Xi_{c}^{+}\to p\phi$ with $\phi\to K^{+}K^{-}$ is observed for the first time, with a statistical significance of more than fifteen standard deviations. The data sample used in this analysis corresponds to an integrated luminosity of 2 fb$^{-1}$ recorded with the LHCb detector in $pp$ collisions at a centre-of-mass energy of 8 TeV. The ratio of branching fractions between the decay $\Xi_{c}^{+}\to p\phi$ and the singly Cabibbo-suppressed decay $\Xi_{c}^{+}\to pK^{-}\pi^{+}$ is measured to be \begin{equation*} \frac{\mathcal{B}(\Xi_{c}^{+}\to p\phi)}{\mathcal{B}(\Xi_{c}^{+}\to pK^{-}\pi^{+})} = (19.8 \pm 0.7 \pm 0.9 \pm 0.2) \times 10^{-3}, \end{equation*} where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the $\phi\to K^{+}K^{-}$ branching fraction.

Figures and captions

Tree quark diagram for the $\Xi ^+_ c \!\rightarrow p \phi $ decay.

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(Left) Fit results for the $\Xi ^+_ c \!\rightarrow p K ^- K ^+ $ decay. The candidates are selected in the $\phi $ meson region, i.e. with the requirement of $ M_{ K ^- K ^+ } <1.07 {\mathrm{\,GeV\!/}c^2} $. The red dotted line corresponds to the signal component, the black dashed line reflects the background distribution, and the blue solid line is their sum. (Right) Background subtracted $ K ^- K ^+ $ mass distribution for the $\Xi ^+_ c \!\rightarrow p K ^- K ^+ $ decay. The red dotted line shows the $\Xi ^+_ c \!\rightarrow p \phi $ contribution, the black dashed line represents the non- $\phi $ contribution, and the solid blue line is the total fit function.

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Fit results for the $\Xi ^+_ c \!\rightarrow p K ^- \pi ^+ $ decay. The red dotted line corresponds to the signal component, the black dashed line reflects the background distribution and the blue solid line is their sum.

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Animated gif made out of all figures.

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Tables and captions

Systematic uncertainties relative to the central value of the ratio $R_{p\phi}$.

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Created on 16 February 2019.Citation count from INSPIRE on 21 February 2019.