Scientists have discovered a new elementary particle - a rare tetraquark consisting of four distinct types or 'flavours' of quarks.
Quarks are point-like elementary particles that typically come in packages of two or three, the most familiar of which are the proton and neutron (each is made of three quarks).
Tetraquarks - four quarks together - are much rarer and are not well understood.
There are six types, or "flavours," of quark to choose from - up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart.
While all other observed tetraquarks contain at least two of the same flavour, the new particle X(5568) has four different flavours - up, down, strange and bottom.
"It is exciting to discover a new and unusual particle that will help us understand the strong interaction - one of the four known fundamental interactions in physics," said Iain Bertram, professor at the Lancaster University in UK.
The tetraquark observation came as a surprise when scientists, involved in the DZero collaboration at the US Fermi National Accelerator Laboratory, first saw hints in July last year of the new particle X(5568) named for its mass - 5568 megaelectronvolts.
Researchers worked on the analysis, developing the model used to simulate the X(5568).
