First observation of the radiative decay $\Lambda_{b}^{0} \to \Lambda \gamma$

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The radiative decay $\Lambda_{b}^{0} \to \Lambda \gamma$ is observed for the first time using a data sample of proton-proton collisions corresponding to an integrated luminosity of $1.7 fb^{-1}$ collected by the LHCb experiment at a center-of-mass energy of $13 TeV$. Its branching fraction is measured exploiting the $B^{0} \to K^{*0} \gamma$ decay as a normalization mode and is found to be $\mathcal{B}(\Lambda_{b}^{0} \to \Lambda \gamma)= (7.1 \pm 1.5 \pm 0.6 \pm 0.7) \times 10^{-6}$, where the quoted uncertainties are statistical, systematic and systematic from external inputs, respectively. This is the first observation of a radiative decay of a beauty baryon.

Figures and captions

Simultaneous fit to the (left) $\Lambda ^0_ b \rightarrow \Lambda \gamma $ and (right) $ B ^0 \rightarrow K ^{*0} \gamma $ invariant-mass distributions of selected candidates. The data are represented by black dots and the result of the fit by a solid blue curve while individual contributions are represented in different line styles (see legend).

data_s[..].pdf [19 KiB]
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data_s[..].pdf [34 KiB]
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Animated gif made out of all figures.


Tables and captions

Dominant systematic uncertainties on the measurement of $\mathcal{B} (\Lambda ^0_ b \rightarrow \Lambda \gamma )$ . The uncertainties arising from external measurements are given separately.

Table_1.pdf [69 KiB]
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Created on 15 June 2019.Citation count from INSPIRE on 15 June 2019.