An exotic particle made up of five quarks has been discovered a decade after experiments seemed to rule out its existence. The short-lived ‘pentaquark’ was spotted by researchers analysing data on the decay of unstable particles in the LHCb experiment at the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva. The finding, says LHCb spokesperson Guy Wilkinson, opens a new era in physicists’ understanding of the strong nuclear force that holds atomic nuclei together. “The pentaquark is not just any new particle — it represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons...