In 2015, the LHCb collaboration reported the observation of significant structures in the $J/\psi p$ final state in a sample of $\Lambda_b^0 -> J/\psi p K^-$ decays using Run 1 data, and showed that the structures could only be explained by the presence of exotic hadrons (pentaquarks). This was a major turning point in the exotic baryon spectroscopy. In this seminar, an update of the study with the full Run 1 and 2 data set collected by the LHCb detector will be presented. With the additional data, a new pentaquark state is observed and the structure reported previously is found to be more complex. Possible interpretations will be also discussed.
Michelangelo Mangano, Monica Pepe-Altarelli and Guillaume Unal