The decays $ Lambda_b^0 to psi(2S)pK^-$ and $ Lambda_b^0 to J/psi pi^+ pi^- pK^-$ are observed in a data sample corresponding to an integrated luminosity of 3fb$^{-1}$, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies by the LHCb detector. The $psi(2S)$ mesons are reconstructed through the decay modes $psi(2S)tomu^+mu^-$ and $psi(2S)to J/psipi^+pi^-$. The branching fractions relative to that of $ Lambda_b^0 to J/psi pK^-$ are measured to be begin{eqnarray*} frac{mathcal{B}(Lambda_b^0 to psi(2S) pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.70pm 0.76pm 0.46pm 0.37)times10^{-2} ,, frac{mathcal{B}(Lambda_b^0 to J/psi pi^+ pi^- pK^-)} {mathcal{B}(Lambda_b^0 to J/psi pK^-)} & = & (20.86pm 0.96pm 1.34)times10^{-2} ,, end{eqnarray*} where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of $J/psi$ and $psi(2S)$ branching fractions. The mass of the $Lambda_b^0$ baryon is measured to be $$ M(Lambda_b^0) = 5619.65 pm 0.17 pm 0.17mathrm{MeV}/c^2,$$ where the uncertainties are statistical and systematic.
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