The Large Hadron Collider has discovered new sub-atomic particles that could help to explain how the centres of atoms are held together.
The particles are all different forms of the so-called Omega-c baryon, whose existence was confirmed in 1994.
Physicists had always believed the various types existed but had not been able to detect them - until now.
The discovery will shed light on the operation of the "strong force", which glues the insides of atoms.
The centres of atoms consist of particles called neutrons and protons. They in turn are made up of smaller particles called quarks, which have unusual names.
Those inside neutrons and protons are called "Up" and "Down". These quarks are held together by the nuclear strong force. Physicists have a theory called quantum chromodynamics for how the nuclear strong force works but using it to make predictions requires very complex calculations.
The Omega-c baryon is in the same family of particles as the neutron and proton, but it can be thought of as a more exotic cousin. It too is made up of quarks but they are called "Charm" and "Strange", and they are heavier versions of the Up and Down quarks.
Since the Omega-c particle's discovery, it was thought that there were heavier versions. Its bigger brothers and sisters if you like. Now, physicists at the European Organization for Nuclear Research (Cern) have found them. They believe that by studying these siblings, they'll learn more about the workings of the nuclear strong force.
Dr Greig Cowan, of the University of Edinburgh, UK, who works on the LHCb experiment at Cern's LHC, said: "This is a striking discovery that will shed light on how quarks bind together. It may have implications not only to better understand protons and neutrons, but also more exotic multi-quark states, such as pentaquarks and tetraquarks."
Prof Tara Shears, of Liverpool University, who also works on the experiment, said: "These particles have been hiding in plain sight for years, but it has taken the exquisite sensitivity of the LHCb to bring them to our attention."
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