  An observation of the $\Lambda_b^0 \rightarrow \psi(2S) \Lambda^0$ decay and
a comparison of its branching fraction with that of the $\Lambda_b^0
\rightarrow J/\psi \Lambda^0$ decay has been made with the ATLAS detector in
proton--proton collisions at $\sqrt{s}=8\,$TeV at the LHC using an integrated
luminosity of $20.6\,$fb$^{-1}$. The $J/\psi$ and $\psi(2S)$ mesons are
reconstructed in their decays to a muon pair, while the $\Lambda^0\rightarrow
p\pi^-$ decay is exploited for the $\Lambda^0$ baryon reconstruction. The
$\Lambda_b^0$ baryons are reconstructed with transverse momentum $p_{\rm
T}>10\,$GeV and pseudorapidity $|\eta|<2.1$. The measured branching ratio of
the $\Lambda_b^0 \rightarrow \psi(2S) \Lambda^0$ and $\Lambda_b^0 \rightarrow
J/\psi \Lambda^0$ decays is $\Gamma(\Lambda_b^0 \rightarrow
\psi(2S)\Lambda^0)/\Gamma(\Lambda_b^0 \rightarrow J/\psi\Lambda^0) = 0.501\pm
0.033 ({\rm stat})\pm 0.019({\rm syst})$, lower than the expectation from the
covariant quark model.
