UC Santa Cruz

The decays Λb0 → ψ(2S)pK− and Λb0 → J/ψπ+π−pK− are observed in a data sample corresponding to an integrated luminosity of 3 fb−1, collected in proton-proton collisions at 7 and 8 TeV centre-of-mass energies by the LHCb detector. The ψ(2S) mesons are reconstructed through the decay modes ψ(2S) → μ+μ− and ψ(2S) → J/ψπ+π−.The branching fractions relative to that of Λb0 → J/ψpK− are measured to be ℬΛb0→ψ2SpK−ℬΛb0→J/ψpK−=20.70±0.76±0.46±0.37×10−2,$$ \frac{\mathrm{\mathcal{B}}\left({\varLambda}_{\mathrm{b}}^0\to \psi \left(2\mathrm{S}\right){\mathrm{pK}}^{-}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_{\mathrm{b}}^0\to \mathrm{J}/\psi\;{\mathrm{pK}}^{-}\right)}=\left(20.70\pm 0.76\pm 0.46\pm 0.37\right)\times {10}^{-2}, $$ where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of J/ψ and ψ(2S) branching fractions. The mass of the Λb0 baryon is measured to be MΛb0=5619.65±0.17±0.17MeV/c2,$$ M\left({\varLambda}_{\mathrm{b}}^0\right)=5619.65\pm 0.17\pm 0.17\ \mathrm{M}\mathrm{e}\mathrm{V}/{c}^2, $$ where the uncertainties are statistical and systematic.