Scientists operating on the LHCb experiment at CERN's Large Hadron Collider announced today the discovery of a new class of subatomic particle: the pentaquark, made up of five quarks.
Quarks are the tiny ingredients of sub-atomic particles such as protons and neutrons, which are made of three quarks. The less common and more unstable mesons, particles found in cosmic rays, have four.
“Benefitting 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 physicist Tomasz Skwarnicki of Syracuse University in a statement from CERN.
"More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark.”
This discovery could contribute to the theory of supersymmetry, which expands on the standard model of particle physics essentially confirmed by the discovery of the Higgs Boson at the Collider in 2013.
“The pentaquark is not just any new particle,” said LHCb spokesperson Guy Wilkinson. “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.”
The quark, which was named after a word in the James Joyce book Finnegans Wake, was first proposed in 1964 by scientists Murray Gell-Mann and George Zweig as the building block inside baryons (particles like protons and neutrons) in three-quark groups; and inside another category of particle, mesons, in quark-antiquark pairs (antiquarks are a form of antimatter).
Gell-Mann's model also included quark composite states such as the pentaquarks.
“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.”
The scientists who authored the paper announcing this discovery say they found two resonances consistent with pentaquarks.
"Earlier experiments that have searched for pentaquarks have proved inconclusive," CERN said in a press release. "Where the LHCb experiment differs is that it has been able to look for pentaquarks from many perspectives, with all pointing to the same conclusion. It’s as if the previous searches were looking for silhouettes in the dark, whereas LHCb conducted the search with the lights on, and from all angles. The next step in the analysis will be to study how the quarks are bound together within the pentaquarks."
The Large Hadron Collider is a 17-mile underground particle accelerator that began operations in 2010.
Visit CERN's website for more information.
Additional reporting by Reuters.