Observation of a new baryon state in the $Lambda_b^0pi^+pi^-$ mass spectrum

A new baryon state is observed in the $Lambda_b^0pi^+pi^-$ 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.