After 50 years, the hunt is over.
Scientists at the Large Hadron Collider, the world's largest atom smasher, have found proof of the existence of the pentaquark, an elusive subatomic particle that was first proposed to exist more than 50 years ago.
"The pentaquark is not just any new particle," Guy Wilkinson, a spokesperson for the LHC experiment that discovered the pentaquark, said in a statement.
"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." [See Photos of the World's Largest Atom Smasher (Large Hadron Collider)]
The new discovery validates a long-held notion about the nature of matter. In 1964, physicist Murray Gell-Mann proposed that a group of particles known as baryons, which include protons and neutrons, are actually made up of three even tinier charged subatomic particles known as quarks. Meanwhile, the theory went, another group of particles called mesons were composed of quarks and their antimatter partners, antiquarks.
The theory was soon validated by experimental results, and Gell-Mann's work won the Nobel Prize in physics in 1969. But crunching the numbers in Gell-Mann's theory also led to the conclusion that other, more exotic particles could exist, such as the pentaquark: a group of four quarks and an antiquark. Over the past several decades, people have seen hints of pentaquarks in experimental data, but those all turned out to be false leads.
In the current study, Wilkinson and his colleagues examined the decay of particles after collisions in the Large Hadron Collider (LHC), a 17-mile-long (27 kilometers) underground ring beneath Geneva, Switzerland. The team studied how a particular baryon known as lambda B decayed into three other particles: a proton, a particle known as J-psi and a charged kaon.
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