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Observation of the $\Lambda_b^0\to\Lambda\phi$ decay

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Abstract

The $\Lambda_b^0\to\Lambda\phi$ decay is observed using data corresponding to an integrated luminosity of 3.0fb$^{-1}$ recorded by the LHCb experiment. The decay proceeds at leading order via a $b\to s\bar{s}s$ loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of $5.9$ standard deviations. The value of the branching fraction is measured to be $(5.18\pm1.04\pm0.35 ^{+0.67}_{-0.62})\times10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.

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Feynman diagram contributing to the $\Lambda ^0_ b \rightarrow \Lambda \phi$ decay.

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Fit projections to the $ { p \pi ^- K ^+ K ^- } $ invariant mass in the (a) long and (b) downstream datasets, the $ { K ^+ K ^- } $ invariant mass in the (c) long and (d) downstream datasets, and the $ { p \pi ^- } $ invariant mass in the (e) long and (f) downstream datasets. The total fit projection is given by the blue solid line. The blue and green dotted lines represent the $\phi$ + $\Lambda $ and pure combinatorial fit components, respectively. The red and magenta dashed lines represent the $\Lambda ^0_ b \rightarrow \Lambda \phi $ signal and the $\Lambda ^0_ b \rightarrow \Lambda K ^+ K ^- $ non-resonant components, respectively. Black points represent the data. Data uncertainties are Poisson 68% confidence intervals.

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Fit projections to the $ {\pi ^+ \pi ^- K ^+ K ^- } $ invariant mass in the (a) long and (b) downstream datasets, the $ { K ^+ K ^- } $ invariant mass in the (c) long and (d) downstream datasets, and the { $ {\pi ^+ \pi ^- } $ } invariant mass in the (e) long and (f) downstream datasets. The total fit projection is given by the blue solid line. The green and blue dotted lines represent the combinatorial and $ K ^0_{\mathrm{ \scriptscriptstyle S}}$ + random $ K ^+$ $ K ^-$ fit components, respectively. The red and magenta dashed lines represent the $ B ^0 \rightarrow K ^0_{\mathrm{ \scriptscriptstyle S}} \phi $ signal and the $ B ^0 \rightarrow K ^0_{\mathrm{ \scriptscriptstyle S}} K ^+ K ^- $ non-resonant components, respectively. Black points represent the data. Data uncertainties are Poisson 68% confidence intervals.

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Decay angles for the $\Lambda ^0_ b \rightarrow \Lambda \phi$ decay, where the angles are defined in the text.

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Distributions of the angular observables: (a) $\sin\Phi_{n_\Lambda }$, (b) $\cos\Phi_{n_\Lambda }$, (c) $\sin\Phi_{n_\phi}$, (d) $\cos\Phi_{n_\phi}$ from weighted $\Lambda ^0_ b \rightarrow \Lambda \phi$ data.

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Animated gif made out of all figures.

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Tables and captions

Systematic uncertainty contributions to the branching fraction ratio.

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Asymmetries measured from $\Lambda ^0_ b \rightarrow \Lambda \phi$ data events.

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Systematic uncertainty contributions to the triple-product asymmetries.

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Created on 21 October 2019.