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Search for the doubly charmed baryon $\Xi_{cc}^{+}$

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Abstract

A search for the doubly charmed baryon $\Xi_{cc}^{+}$ is performed through its decay to the $\Lambda_c^+ K^- \pi^+$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13$\mathrm{ Te V}$. The data correspond to a total integrated luminosity of $9 \mathrm{fb}^{-1}$. No significant signal is observed in the mass range from 3.4 to 3.8$\mathrm{ Ge V}/c^2$. Upper limits are set at $95\%$ credibility level on the ratio of the $\Xi_{cc}^{+}$ production cross-section times the branching fraction to that of $\Lambda_c^+$ and $\Xi_{cc}^{++}$ baryons. The limits are determined as functions of the $\Xi_{cc}^{+}$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15$\mathrm{ Ge V}/c$.

Figures and captions

Mass distributions of the (left) intermediate $\Lambda ^+_ c $ and (right) $\Xi _{ c c }^{+}$ candidates for the full data sample. Selection A is applied, including the $\Lambda ^+_ c $ mass requirement, indicated by the cross-hatched region in the left plot, of $2270\text{ Me V /}c^2 <M([ p K ^- \pi ^+ ]_{\Lambda ^+_ c })<2306\text{ Me V /}c^2 $. The right-sign (RS) $m(\Lambda ^+_ c K ^- \pi ^+ )$ distribution is shown in the right plot, along with the wrong-sign (WS) $m(\Lambda ^+_ c K ^- \pi ^- )$ distribution normalised to have the same area. The dotted red line at 3518.7 $\text{ Me V /}c^2$ indicates the mass of the $\Xi _{ c c }^{+}$ baryon reported by SELEX [42] and the dashed blue line at 3621.2 $\text{ Me V /}c^2$ indicates the mass of the isospin partner, the $\Xi _{ c c }^{++}$ baryon [48].

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Local $p$-value (statistical only) at different $\Xi _{ c c }^{+} $ mass values evaluated with the likelihood-ratio test, for the data sets recorded at $\sqrt{s}=7\text{ Te V} $, $\sqrt{s}=8\text{ Te V} $ and $\sqrt{s}=13\text{ Te V} $. Selection A is applied, including the $\Lambda ^+_ c $ mass requirement of $2270\text{ Me V /}c^2 <M([ p K ^- \pi ^+ ]_{\Lambda ^+_ c })<2306\text{ Me V /}c^2 $.

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Distributions of (left) $M([ p K ^- \pi ^+ ]_{\Lambda ^+_ c })$ and (right) $\log_{10}(\chi^2_{\text{IP}} )$ of the selected $\Lambda ^+_ c $ candidates with associated fit results for the 2018 data set.

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Mass distribution of $\Xi _{ c c }^{++} $ candidates in the 2018 data set. The result of a fit to the distribution is shown.

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Upper limits on (left) $\mathcal{R}(\Lambda ^+_ c )$ and (right) $\mathcal{R}(\Xi _{ c c }^{++} )$ at 95% credibility level as a function of $m(\Lambda ^+_ c K ^- \pi ^+ )$ at $\sqrt{s}=8\text{ Te V} $ for four $\Xi _{ c c }^{+} $ lifetime hypotheses.

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Upper limits on (left) $\mathcal{R}(\Lambda ^+_ c )$ (right) $\mathcal{R}(\Xi _{ c c }^{++} )$ at 95% credibility level as a function of $m(\Lambda ^+_ c K ^- \pi ^+ )$ at $\sqrt{s}=13\text{ Te V} $, for four $\Xi _{ c c }^{+} $ lifetime hypotheses.

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Animated gif made out of all figures.

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Tables and captions

Signal yields for prompt $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ and $\Xi _{ c c }^{++} \rightarrow \Lambda ^+_ c K ^- \pi ^+ \pi ^+ $ normalisation modes, split by data-taking period. The integrated luminosity $\mathcal{L}$ is also shown for each data-taking period.

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Efficiency ratios between the normalisation and signal modes for different data-taking periods. The uncertainties are due to the limited size of the simulated samples.

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Single-event sensitivity of the $\Lambda ^+_ c $ normalisation mode $\alpha(\Lambda ^+_ c )$ [$\times 10^{-5}$] for different lifetime hypotheses of the $\Xi _{ c c }^{+} $ baryon in the different data-taking years. The uncertainties are due to the limited sizes of the simulated samples and the statistical uncertainties on the measured $\Lambda ^+_ c $ baryon yields.

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Single-event sensitivity of the $\Xi _{ c c }^{++}$ normalisation mode $\alpha(\Xi _{ c c }^{++} )$ [$\times 10^{-2}$] for different lifetime hypotheses of the $\Xi _{ c c }^{+} $ baryon in the different data-taking years. The uncertainties are due to the limited size of the simulated samples and the statistical uncertainty on the measured $\Xi _{ c c }^{++}$ baryon yield.

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Summary of the systematic uncertainties of the production ratio measurement.

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Summary of the largest upper limits on production ratios at 95% credibility level for four lifetime hypotheses and different centre-of-mass energies.

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Supplementary Material [file]

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2019-019. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats

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Created on 27 February 2021.