Observation of penta-quarks with the LHCb experiment

The analysis of the experimental data collected by the LHCb experiment between 2011 and 2012 has led to the discovery of a new particle composed of 5 quarks, 2 of which being charmed. Although this composition is allowed by the theory of strong interactions it is the first time it is observed. The penta-quark has been discovered through a thorough analysis of the data corresponding to the following decay channel of Λ_b⁰: Λ_b⁰ → J/ψK^-p. The analysis shows that some decays were in fact: Λ_b⁰ → P_c⁺K^- where P_c⁺ is a charmed particle composed of 5 quarks and whose mass is (4380 ± 30) MeV and spin is 3/2^-. Data shows also the presence of a second resonance at (4450 ± 3) MeV. (A.C.)