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Observations of $\Lambda_b^0 \to \Lambda K^+\pi^-$ and $\Lambda_b^0 \to \Lambda K^+K^-$ decays and searches for other $\Lambda_b^0$ and $\Xi_b^0$ decays to $\Lambda h^+h^{\prime -}$ final states

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Abstract

A search is performed for the charmless three-body decays of the $\Lambda_b^0$ and $\Xi_b^0$ baryons to the final states $\Lambda h^+h^{\prime -}$, where $h^{(\prime)} = \pi$ or $K$. The analysis is based on a data sample, corresponding to an integrated luminosity of $3 \rm fb^{-1}$ of $pp$ collisions, collected by the LHCb experiment. The $\Lambda_b^0 \to \Lambda K^+\pi^-$ and $\Lambda_b^0 \to \Lambda K^+K^-$ decays are observed for the first time and their branching fractions and $CP$ asymmetry parameters are measured. Evidence is seen for the $\Lambda_b^0 \to \Lambda \pi^+\pi^-$ decay and limits are set on the branching fractions of $\Xi_b^0$ baryon decays to the $\Lambda h^+h^{\prime -}$ final states.

Figures and captions

Results of the fit for the (left) $\Lambda ^0_ b \rightarrow \left(\Lambda \pi ^+ \right)_{\Lambda ^+_ c }\pi ^- $ control mode and (right) $\Lambda \pi ^+ \pi ^- $ signal final states, for all subsamples combined. Superimposed on the data are the total result of the fit as a solid blue line, the $\Lambda ^0_ b $ ( $\Xi ^0_ b $ ) decay as a short-dashed black (double dot-dashed grey) line, cross-feed as triple dot-dashed brown lines, the combinatorial background as a long-dashed green line, and partially reconstructed background components with either a missing neutral pion as a dot-dashed purple line or a missing soft photon as a dotted cyan line.

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Results of the fit for the (left) $\Lambda K ^\pm \pi ^\mp $ and (right) $\Lambda K ^+ K ^- $ final states, for all subsamples combined. Superimposed on the data are the total result of the fit as a solid blue line, the $\Lambda ^0_ b $ ( $\Xi ^0_ b $ ) decay as a short-dashed black (double dot-dashed grey) line, cross-feed as triple dot-dashed brown lines, the combinatorial background as a long-dashed green line, and partially reconstructed background components with either a missing neutral pion as a dot-dashed purple line or a missing soft photon as a dotted cyan line.

Lb2LzK[..].pdf [23 KiB]
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Background-subtracted and efficiency-corrected Dalitz plot distributions for (left) $\Lambda ^0_ b \rightarrow \Lambda K ^+ \pi ^- $ and (right) $\Lambda ^0_ b \rightarrow \Lambda K ^+ K ^- $ with data from all subsamples combined. Boxes with a cross indicate negative values.

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Animated gif made out of all figures.

PAPER-2016-004.gif
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Tables and captions

Signal yields for the $\Lambda ^0_ b $ and $\Xi ^0_ b $ decay modes under investigation. The totals are simple sums and are not used in the analysis.

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Systematic uncertainties (in units of $10^{-3}$) on the branching fraction ratios reported in Sec. 6. The total is the sum in quadrature of all contributions.

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Systematic uncertainties on ${\cal A}_{ C\!P }$ (in units of $10^{-3}$).

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Supplementary Material [file]

Supplementary material full pdf

supple[..].pdf [523 KiB]
supplementary.pdf

This ZIP file contains supplementary material for the publication LHCb-PAPER-2016-004. 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 09 December 2018.Citation count from INSPIRE on 09 December 2018.