Scientists at CERN's Large Hadron Collider today announced the discovery of a new class of exotic subatomic particles called the pentaquarks.
Pentaquark was first predicted to exist in the 1960s but, much like the Higgs boson particle before it, the particle eluded science for decades until its detection at the LHC.
"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," added Wilkinson. "Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we're all made, is constituted," he said.
Understanding of the structure of matter was revolutionised in 1964 when US physicist Murray Gell-Mann proposed that a category of particles known as baryons, which includes protons and neutrons, are comprised of three fractionally charged objects called quarks, and that another category, mesons, are formed of quark-antiquark pairs. Gell-Mann was awarded the Nobel Prize in physics for this work in 1969. This quark model also allows the existence of other quark composite states, such as pentaquarks composed of four quarks and an antiquark.
Earlier experiments that have searched for pentaquarks have proved inconclusive. 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, CERN said. The next step in the analysis will be to study how the quarks are bound together within the pentaquarks.
"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 physicist Tomasz Skwarnicki of Syracuse University. "More precisely the states must be formed of two up quarks, one down quark, one charm quark and one anti-charm quark," added Skwarnicki.
The findings appear in the journal Physical Review Letters.
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