Observation of the decay Lambda(0)(b) -> psi(2S)p pi(-)

The Cabibbo-suppressed decay Lambda(0)(b) -> psi(2S)p pi(-) is observed for the fi rst 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 13TeV, respectively. The psi(2S) mesons are reconstructed in the mu(+)mu(-) fi nal state. The branching fraction with respect to that of the Lambda(0)(b) -> psi(2S)pK(-) decay mode is measured to be B (Lambda(0)(b) -> psi(2S)p pi(-))/B (Lambda(0)(b) -> psi(2S)pK(-)) = (11.44 +/- 1.3 +/- 0.2)%, where the fi rst uncertainty is statistical and the second is systematic. The psi(2S) p and psi(2S)pi(-) mass spectra are investigated and no evidence for exotic resonances is found.