12 Matter Particles Suffice in Nature: Limited Number of Fermions in Standard Model?

How many matter particles exist in nature? Particle physicists have been dealing with this question for a long time. The 12 matter particles contained in the standard model of particle physics? Or are there further particles with too high a mass to be produced by the experiments performed so far? These questions are now answered by researchers of KIT, CERN, and Humboldt University in the current issue of the Physical Review Letters

Science Daily - Dec. 13, 2012

Physical Review Letters, 2012; 109 (24) DOI :10.1103/PhysRevLett.109.241802