Scientists at the European Organization for Nuclear Research (CERN) have made their first major discovery since the restart of the Large Hadron Collider, proving the existence of a long theorized new class of subatomic particles known as pentaquarks.
According to BBC News, pentaquarks were first predicted to exist more than five decades ago, but evidence of its existence had alluded scientists until it was detected by the particle collider’s LHCb experiment on Tuesday. A paper detailing the CERN team’s findings is now available on the arXiv website and has been submitted to the journal Physical Review Letters.
This short-lived pentaquark was detected by physicists analyzing data on the decay of unstable particles in the accelerator’s LHCb experiment near Geneva, Nature explained. Guy Wilkinson, a spokesperson for the experiment, told the publication that the discovery will launch a new era in scientists’ understanding of the nuclear forces that bind atomic nuclei.
“The pentaquark is not just any new particle,” Wilkinson said. “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 fifty 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.”
Signals could ‘only be explained’ by pentaquarks
The existence of quarks, charged subatomic particles that join together to form larger particles such as protons and neutrons, was first proposed by physicists Murray Gell Mann and George Zweig in 1964. They independently theorized that the key properties of particles called baryons and mesons could best be explained is they were made up of other constituent particles.
Mann and Zweig proposed three types of these “hypothesized building blocks,” BBC News said, but their model also allowed for the existence of other quark states, including the pentaquark. On Tuesday, CERN researchers found proof of these pentaquarks by watching the decay of a bayron known as Lambda b into three other particles: a J-psi, a proton, and a charged kaon.
In doing so, they observed a transition state in which they were able to identify to intermediate states that were sometimes involved in the production of the three particles. They have dubbed those states Pc(4450)+ and Pc(4380)+, with the former being clearly visible in the data and the latter being required to fully described their findings.
LHCb physicist Tomasz Skwarnicki of Syracuse University told BBC News that the team had “examined all possibilities for these signals” and concluded “that they can only be explained by pentaquark states.” His colleague Patrick Koppenburg, LHCb physics coordinator at CERN, added that there was “no way” that the observations “could be due to something else other than the addition of a new particle that was not observed before.”