The pentaquark is an elusive subatomic particle that was theorized by physicists five decades ago but never seen until now. Researchers using the Large Hadron Collider believe they have now uncovered the mysterious particle.

Quarks are tiny subatomic particles that compose neutrons and protons found in the nucleus of atoms. Three quarks go into each of the larger composite particles. They were first predicted by the physicist Murray Gell-Mann in the 1960s. However, in addition to the normal three-quark particle, physicists also realized particles could also be composed of five of these building blocks, and they labeled the theoretical particles "pentaquarks." Although earlier experiments claimed to show evidence of these pentaquarks, further research showed each of those reports were in error.

"There is quite a history with pentaquarks, which is also why we were very careful in putting this paper forward. It's just the word 'pentaquark' which seems to be cursed somehow because there have been many discoveries that were then superseded by new results that showed that previous ones were actually fluctuations and not real signals," Patrick Koppenburg, from the European Organization for Nuclear Research (CERN), said.

When Gell-Mann proposed the idea of quarks, he realized that three of these constituent particles are required for the formation of a class of particles called baryons, which include neutrons and protons. A quark and an anti-quark can also join together to form a meson, but these are highly unstable, falling apart in a small fraction of a second. Theoretical physics reveals that pentaquarks would contain four quarks and a single anti-matter version of the building blocks.

Gell-Mann named quarks after a line from the poem Finnegan's Wake by James Joyce: "Three quarks for Muster Mark." The physicist with a quirky sense of humor also provided odd names for the six varieties of the component particles. These types of quarks are known as up, down, bottom, top, strange and charm. Each of these varieties also exist in anti-matter forms. Pentaquarks are composed of two up, one down, one charm and one anti-charm quarks.

"The pentaquark is not just any new particle. It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over 50 years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we're all made, is constituted," said LHCb spokesperson Guy Wilkinson.

The Higgs boson, believed to provide matter with mass, was another particle theorized to exist long before being discovered by scientists at the LHC.

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