Pentaquarks and tetraquarks at LHCb

Exotic resonant structures found in Λ⁰ _b and B⁰ decays into charmonium in the LHCb experiment are discussed. Examination of the J/Φ system in Λ⁰ _b → J/ΦK^-p decays shows two states each of which must be composed of uudcc quarks, and thus are called charmonium pentaquarks. Their masses are 4380 ± 8 ± 29 MeV and 4449.8 ± 1.7 ± 2.5 MeV, and their corresponding widths (T) are 205 ± 18 ± 86 MeV, and 39 ± 5 ± 19 MeV. The preferred J^P assignments are of opposite parity, with one state having spin 3/2 and the other 5/2. Models of internal binding of the pentaquark states are discussed. Finally, another mesonic state is discussed, the Z(4430)^- that decays into Φ' π^- and was first observed by the Belle collaboration in B⁰ → Φ'K⁺π^- decays. Using a sample of approximately 25,000 signal events, LHCb determines the J^P to be 1⁺.