Description
Bound QCD states that involve 5 quarks, though long anticipated, did not appear until 2015 when LHCb found two significant enhancements in the $J/\psi p$ invariant mass spectrum ($ccbar + uud$) in the decays of $\Lambda_b$.
The Run-II data comes with surprises: the reanalysis of the same reaction with an order of magnitude larger statistics nearly doubles the number of established Pentaquarks states. The fact that new states are very narrow and are located close to the $\Sigma_c^{(*)} \overline{D}$ threshold hints at their molecular (meson+baryon) nature. However, a subtle point that had to be considered in the analysis is the role played by triangle singularities in the final-state interaction, potentially giving rise to a $\Sigma_c^{(*)} \overline{D}$ threshold enhancement.
In the talk I will discuss details of the latest analysis as well as several theoretical investigations on the nature of new states. We will consider if the states can be observed elsewhere, and speculate as to whether LHCb will once more double the number of Pentaquarks with the Run-III data.
