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Search for the doubly charmed baryon $\it{\Xi}_{cc}^{+}$ in the $\it{\Xi}_{c}^{+} \pi^{-} \pi^{+}$ final state

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Abstract

A search for the doubly charmed baryon $\it{\Xi}_{cc}^{+}$ is performed in the $\it{\Xi}_{c}^{+} \pi^{-} \pi^{+}$ invariant-mass spectrum, where the $\it{\Xi}_{c}^{+}$ baryon is reconstructed in the $p K^{-} \pi^{+}$ final state. The study uses proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 13$\mathrm{ Te V}$, corresponding to a total integrated luminosity of 5.4$ \mathrm{fb}^{-1}$. No significant signal is observed in the invariant-mass range of 3.4$-$3.8$\mathrm{ Ge V}/c^2$. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the $\it{\Xi}_{cc}^{++} \rightarrow (\it{\Xi}_{c}^{+} \rightarrow p K^{-} \pi^{+}) \pi^{+}$ decay for different $\it{\Xi}_{cc}^{+}$ mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25$\mathrm{ Ge V}/c$. The results from this search are combined with a previously published search for the $\it{\Xi}_{cc}^{+} \rightarrow \it{\Lambda}_{c}^{+} K^{-} \pi^{+}$ decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620$\mathrm{ Me V}/c^2$, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5$-$3.7$\mathrm{ Ge V}/c^2$ mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.

Figures and captions

Examples of diagrams for the $\Xi ^+_{ c c } \rightarrow \Xi ^+_ c \pi ^- \pi ^+ $ decay.

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Invariant-mass spectrum for the $\Xi ^+_ c \pi ^- \pi ^+ $ (black points) and the $\Xi ^+_ c \pi ^- \pi ^- $ (green squares) final states for the default trigger set. The $\Xi ^+_ c \pi ^- \pi ^- $ data are normalised to the $\Xi ^+_ c \pi ^- \pi ^+ $ invariant-mass spectrum.

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Local $p$-values as a function of the $\Xi ^+_{ c c }$ invariant mass, for $\Xi ^+_{ c c }$ baryon decays reconstructed in the $\Xi ^+_ c $ $\pi ^-$ $\pi ^+$ (green dashed curve) and $\Lambda ^+_ c $ $ K ^-$ $\pi ^+$ (blue dash-dotted curve) modes, or combining the two modes (black solid curve). The horizontal dotted red lines represent the $p$-values corresponding to significances of 1, 2, 3 and $4 \sigma$. The extended trigger set is used for the $\Xi ^+_{ c c } \rightarrow \Xi ^+_ c \pi ^- \pi ^+ $ decay and Selection B from Ref. [10] is used for the $\Xi ^+_{ c c } \rightarrow \Lambda^+_ c K ^- \pi ^+ $ decay. The systematic uncertainties are not taken into account.

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Invariant mass spectra for the (left) $\Xi ^+_ c $ $\pi ^-$ $\pi ^+$ and (right) $\Lambda^+_ c $ $ K ^-$ $\pi ^+$ final states. The blue solid curve represents the result of a simultaneous fit to the two spectra, with the red dashed (green dotted) curve showing the signal (background) component. The extended trigger set is used for the $\Xi ^+_{ c c } \rightarrow \Xi ^+_ c \pi ^- \pi ^+ $ decay and Selection B from Ref. [10] is used for the $\Xi ^+_{ c c } \rightarrow \Lambda^+_ c K ^- \pi ^+ $ decay.

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Invariant-mass distribution of the $\Xi ^{++}_{ c c } \rightarrow \Xi ^+_ c \pi ^+ $ candidates in the default trigger set. The blue solid line represents the total fit, the red dashed line corresponds to the signal component and the green dotted line to the background component.

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Upper limits on $R$ as a function of the assumed $\Xi ^+_{ c c }$ mass for four different lifetime ($\tau$) hypotheses at 95% CL.

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Animated gif made out of all figures.

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Tables and captions

Single-event sensitivity including both statistical and systematic uncertainties evaluated for different $\Xi ^+_{ c c }$ lifetime hypotheses.

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Systematic uncertainties on the ratio of efficiencies for the upper limit determination.

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2021-019. The files are: supplementary.tex : LaTeX source file of the supplementary material supplementary.pdf : Summary of the supplementary material *.pdf, *.png, *.eps, *.C : The figures in various formats

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Created on 23 March 2024.