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

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## Abstract

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] HiDef png [292 KiB] Thumbnail [247 KiB] data_s[..].pdf [34 KiB] HiDef png [390 KiB] Thumbnail [323 KiB] Animated gif made out of all figures. PAPER-2019-010.gif Thumbnail

## 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] HiDef png [124 KiB] Thumbnail [57 KiB] tex code

Created on 12 October 2019.