The 12 matter particles we know about are all the types there are, according to researchers analysing CERN data.
Matter particles, also called fermions, are the elementary components of the universe, making up everything visible in the universe.
“For a long time, however, it was not clear whether we know all components,” says Professor Ulrich Nierste of Karlsruhe Institute of Technology.
The standard model of particle physics puts the number of fermions at 12 and, based on their properties, they’re divided into three generations of four particles each. Only the first generation – the electron, the electron neutrino, the up-quark and the down-quark – is found in any appreciable quantity outside of particle accelerators.
Up- and down-quarks form heavier particles, such as protons and neutrons and, from here, all elements of the periodic system.
“But why does nature have second and third generations, if these are hardly needed? And are there maybe more generations of particles?” says the team.
To find out, they combined the latest data from the LHC and Tevatron particle accelerators with known measurements relating to particles such as the Z-boson or the top-quark. And the statistical analysis shows that there are no more fermions to be found, with a probability of 99.99999 percent.
A crucial element in all this was the Higgs particle, which gives all other particles their mass. As no new fermions were detected directly in accelerator experiments, they’d have to be heavier than the fermions known so far. This means, though, that they’d interact with the Higgs particle more strongly – modifying its properties in a way that would have made it undetectable.
“Within the standard model the number of fermions is now firmly established,” says Nierste.
