From samples of $pp$ collision data collected by the LHCb experiment at $sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $Lambda_b^0K^-$ and $Xi_b^0pi^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $Xi_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $Xi_b(6227)^-$, the mass and natural width are measured to be $m_{Xi_{b}(6227)^-}=6226.9pm2.0pm0.3pm0.2$ MeV/$c^2$ and $Gamma_{Xi_b(6227)^-}=18.1pm5.4pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{Xi_b(6227)^-}$, is due to the knowledge of the $Lambda_b^0$ baryon mass. Relative production rates of the ${Xi_b(6227)^-toLambda_b^0K^-}$ and ${Xi_b(6227)^-toXi_b^0pi^-}$ decays are also reported.
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