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. Fig_1.pdf [1 KiB] HiDef png [0 KiB] Thumbnail [0 KiB] tex code (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 $M_{ K ^- K ^+ } <1.07 {\mathrm{\,Ge V\!/}c^2}$. 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. Fig_2.pdf [94 KiB] HiDef png [221 KiB] Thumbnail [63 KiB] tex code 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. Fig_3.pdf [73 KiB] HiDef png [96 KiB] Thumbnail [27 KiB] tex code Animated gif made out of all figures. PAPER-2018-040.gif Thumbnail

Tables and captions

 Systematic uncertainties relative to the central value of the ratio $R_{p\phi}$. Table_1.pdf [41 KiB] HiDef png [133 KiB] Thumbnail [20 KiB] tex code

Created on 20 April 2019.Citation count from INSPIRE on 25 April 2019.