Five-quark particle detected at CERN
DOI: 10.1063/PT.5.029036
Nature : More than a decade ago, the detection of a five-quark “petaquark” particle caused a stir among particle physicists, but further experiments seemed to rule out its existence. Now physicists at CERN’s LHCb detector have found the presence of two particles weighing 4.38 GeV and 4.45 GeV in data recorded from 2009 to 2012. Their analysis of the particles suggests that they are different configurations of two up quarks, a down quark, and a charm and anti-charm quark pair. The significance of the signal for the two particles is 9-sigma, far exceeding the 5-sigma needed to make a claim for the discovery of a new particle. The new pentaquark is several times heavier than the one that was apparently found in 2002, so the discovery doesn’t seem to bear on the existence of the earlier particle.
