Scientists at the Large Hadron Collider near Geneva have discovered a previously unseen class of particles that demonstrate there is a new state of matter.

Researchers working on the collider’s LHCb detector spotted signals that are produced when five subatomic particles called quarks combine together to form pentaquarks.



“It is an important result,” said Sheldon Stone, professor of physics at Syracuse University in New York. “It shows that there is a new state of matter. Although pentaquark states were thought possible from the dawn of the quark model, the theory that explains the structure of baryons like the proton, they had never been seen before.”



The discovery was made from data collected before the Large Hadron Collider switched on again earlier this year after a planned upgrade which allowed it to run at higher energy.



Scientists’ understanding of the structure of matter was transformed in 1964 when the American physicist Murray Gell-Mann proposed that protons and neutrons were made up of three new types of particles called quarks. The work earned him the Nobel prize in 1969.



Researchers on the LHCb team found evidence for pentaquarks after studying the disintegration of an unstable ball of three quarks called a Lambda baryon. The exotic pentaquarks they observed are made up of two up quarks, one down quark, one charm quark and one anti-charm quark. Details of the finding are reported today and have been submitted to the journal Physical Review Letters.



Guy Wilkinson, LHCb spokesperson, said the discovery confirms a prediction made by Gell-Mann more than half a century ago. “It’s been a big big puzzle,” he said.



“One place where pentaquarks may be relevant is when stars collapse and form neutron stars, the final stage of collapse before some go on to make black holes.



“In that environment, it’s quite possible that pentaquarks are formed, and if that’s so, it could have significant consequences for what happens to the stars, what they look like and what is their ultimate fate.”



Running at a higher energy than ever, the Large Hadron Collider will give researchers a chance to study the particles in more detail, and to look for other varieties of pentaquark. “Having found one, it’s highly likely there are others out there,” said Wilkinson.

