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Search for the $\Lambda_b^0 \rightarrow \Lambda \eta^\prime$ and $\Lambda_b^0\rightarrow \Lambda \eta$ decays with the LHCb detector

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Abstract

A search is performed for the as yet unobserved baryonic $\Lambda_b \rightarrow \Lambda \eta^\prime$ and $\Lambda_b \rightarrow \Lambda \eta$ decays with 3$fb^{-1}$ of proton-proton collision data recorded by the LHCb experiment. The $B^0 \rightarrow K_S^0 \eta^\prime$ decay is used as a normalisation channel. No significant signal is observed for the $\Lambda_b \rightarrow \Lambda \eta^\prime$ decay. An upper limit is found on the branching fraction of $\mathcal{B}(\Lambda_b \rightarrow \Lambda \eta^\prime)<3.1\times10^{-6}$} at 90% confidence level. Evidence is seen for the presence of the $\Lambda_b \rightarrow \Lambda \eta$ decay at the level of $3\sigma$ significance, with a branching fraction $\mathcal{B}(\Lambda_b \rightarrow \Lambda \eta)=(9.3^{+7.3}_{-5.3})\times10^{-6}$}.

Figures and captions

Feynman diagrams for the $\Lambda ^0_ b \rightarrow \Lambda \eta ^{(\prime)} $ decay. The non-spectator and anomalous diagrams are available only to the $\eta ^{\prime}$ through the gluonic contribution.

LbEtap[..].png [30 KiB]
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LbEtapL_std.png
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LbEtapL_non-spec.png
LbEtap[..].png [38 KiB]
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LbEtapL_anom.png

Mass distribution of the selected $ B ^0 \rightarrow K ^0_{\rm\scriptscriptstyle S} \eta ^{\prime} $ ( $\eta ^{\prime} \rightarrow \pi ^+ \pi ^- \gamma$ ) candidates in the 2011 and 2012 data, reconstructed in the L (left) and D (right) categories. The results of the fit, as described in the text, are overlaid.

Fig2a.pdf [19 KiB]
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Fig2a.pdf
Fig2b.pdf [19 KiB]
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Fig2b.pdf

Mass distribution of the reconstructed $\eta ^{\prime}$ meson for selected $ B ^0 \rightarrow K ^0_{\rm\scriptscriptstyle S} \eta ^{\prime} $ ( $\eta ^{\prime} \rightarrow \pi ^+ \pi ^- \gamma$ ) candidates, in the L (left) and D (right) categories. The results of the fit, as described in the text, are overlaid.

Fig3a.pdf [18 KiB]
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Fig3a.pdf
Fig3b.pdf [18 KiB]
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Fig3b.pdf

Mass distribution of the selected $\Lambda ^0_ b \rightarrow \Lambda \eta ^{\prime} $ ( $\eta ^{\prime} \rightarrow \pi ^+ \pi ^- \gamma$ ) candidates in the 2011 and 2012 data, reconstructed in the L (left) and D (right) categories. The results of the fit, as described in the text, are overlaid.

Fig4a.pdf [17 KiB]
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Fig4a.pdf
Fig4b.pdf [18 KiB]
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Fig4b.pdf

Mass distribution of the selected $\Lambda ^0_ b \rightarrow \Lambda \eta ^{\prime} $ ( $\eta ^{\prime} \rightarrow \pi ^+ \pi ^- \eta $ ) candidates in the 2011 and 2012 data, reconstructed in the L (left) and D (right) categories. The results of the fit, as described in the text, are overlaid.

Fig5a.pdf [17 KiB]
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Fig5a.pdf
Fig5b.pdf [16 KiB]
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Fig5b.pdf

Mass distribution of the selected $\Lambda ^0_ b \rightarrow \Lambda \eta $ ( $\eta \rightarrow \pi ^+ \pi ^- \pi ^0 $ ) candidates in the 2011 and 2012 data, reconstructed in the L (left) and D (right) categories. The results of the fit, as described in the text, are overlaid.

Fig6a.pdf [16 KiB]
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Fig6a.pdf
Fig6b.pdf [17 KiB]
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Fig6b.pdf

Animated gif made out of all figures.

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thumbnail_PAPER-2015-019.gif

Tables and captions

Components contributing to the scale factor $\alpha.$

Table_1.pdf [75 KiB]
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tex code
Table_1.pdf

Fractional systematic uncertainties, in percent, on the ratio of branching fractions.

Table_2.pdf [78 KiB]
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tex code
Table_2.pdf

Created on 15 June 2019.Citation count from INSPIRE on 15 June 2019.