Quarks are the super-small elementary particles that make up the neutrons and protons that make up atoms. (Neutrons and protons are each made of three quarks.) Quarks can also combine to form an array of stranger composite particles, though, such as the pentaquark. Says The Verge:
Like the Higgs boson before it, the pentaquark’s existence has been theorized for years, but experiments in the early-2000s claiming to have detected the exotic form of matter were later invalidated. Many scientists had since given up on the pentaquark for good, but this time, say CERN physicists, there’s no doubt it’s been found.
Although the word “pentaquark” isn’t new, the confirmation of its existence marks an extremely important moment for the scientific community. The history of the pentaquark goes back to 1964. This is when Nobel Prize winner Murray Gell-Man proposed that “quarks” exist in our everyday world. He showed that every proton and neutron is made from combinations of three elementary particles known as quarks, and suggested that it could also be possible to make matter from five quarks, resulting in a pentaquark.
Physicists believe the discovery could shed light on how everyday matter is constituted, and deepen the understanding of the strong nuclear force – one of the four basic forces in nature, along with gravity, electromagnetic force, and the weak nuclear force.
The LHC team is now certain of the pentaquark’s existence. Their discovery actually began a few years ago, while studying the results of particle collisions at the LHC done between 2011 and 2012. This is when the team accidentally encountered a “bump” in the data. That is, a large spike in one of the readings.
“Since the pentaquark has such a bad reputation, we didn’t take it seriously,” said Sheldon Stone, professor of physics at Syracuse University and one of the four members of the LHC team, as quoted by The Wall Street Journal. But after six months of further work, the team decided that it had actually found the elusive pentaquark. “Benefiting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states,” said LHCb scientist Tomasz Skwarnicki, a professor of physics at Syracuse University.
“More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark,” Skwarnicki added. The team is still unsure how the quarks are bound together, and plans to investigate those details in further research. “The quarks could be tightly bound,” said LHCb physicist Liming Zhang of Tsinghua University. “Or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”