Observation of the decay Λb0 → ψ(2S)pπ−

Abstract The Cabibbo-suppressed decay Λb0 → ψ(2S)pπ− is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb−1 of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ+μ− final state. The branching fraction with respect to that of the Λb0 → ψ(2S)pK− decay mode is measured to be ℬΛb0→ψ2Spπ−ℬΛb0→ψ2SpK−=11.4±1.3±0.2%, $$ \frac{\mathrm{\mathcal{B}}\left({\Lambda}_{\mathrm{b}}^0\to \uppsi \left(2\mathrm{S}\right){\mathrm{p}\uppi}^{-}\right)}{\mathrm{\mathcal{B}}\left({\Lambda}_{\mathrm{b}}^0\to \uppsi \left(2\mathrm{S}\right){\mathrm{p}\mathrm{K}}^{-}\right)}=\left(11.4\pm 1.3\pm 0.2\right)\%, $$ where the first uncertainty is statistical and the second is systematic. The ψ(2S)p and ψ(2S)π− mass spectra are investigated and no evidence for exotic resonances is found