  The first observation of two structures consistent with resonances in the
final states $\Lambda_b^0 \pi^-$ and $\Lambda_b^0 \pi^+$ is reported using
samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s} =
7$ and $8$ TeV, corresponding to an integrated luminosity of 3
$\mathrm{fb}^{-1}$. The ground states $\Sigma_b^\pm$ and $\Sigma_b^{*\pm}$ are
also confirmed and their masses and widths are precisely measured.
