  A new baryon state is observed in the $\Lambda_b^0\pi^+\pi^-$ mass spectrum
with high significance using a data sample of $pp$ collisions, collected with
the LHCb detector at centre-of-mass energies $\sqrt{s}=7, 8$ and 13TeV,
corresponding to an integrated luminosity of 9fb$^{-1}$. The mass and natural
width of the new state are measured to be \begin{eqnarray*} m & = & 6072.3 \pm
2.9 \pm 0.6 \pm 0.2 MeV\,, \Gamma & = & 72 \pm 11 \pm 2 MeV\,, \end{eqnarray*}
where the first uncertainty is statistical and the second systematic. The third
uncertainty for the mass is due to imprecise knowledge of the $\Lambda_b^0$
baryon mass. The new state is consistent with the first radial excitation of
the $\Lambda_b^0$ baryon, the $\Lambda_b(2S)^0$ resonance. Updated measurements
of the masses and the upper limits on the natural widths of the previously
observed $\Lambda_b(5912)^0$ and $\Lambda_b(5920)^0$ states are also reported.
