Scientists working on the LHCb experiment at the Large Hadron Collider announced they had confirmed the existence of pentaquarks, subatomic particles composed of five quarks rather than the usual two or three, resolving a question that had lingered since the idea was first proposed in the 1960s. The discovery expanded physicists' understanding of how quarks, the fundamental building blocks of matter, can combine.
Quarks were long known to combine in only two stable configurations: three quarks forming baryons like protons and neutrons, or a quark-antiquark pair forming mesons. Theorists had speculated since Murray Gell-Mann's original quark model that other combinations, including five-quark states, might be possible, but decades of experimental searches had produced only ambiguous, contested hints.
The LHCb collaboration sifted through data from proton collisions and identified a particle they named Pb, consistent with four quarks and one antiquark bound tightly together, observed with a statistical significance far beyond prior claims from the 2000s that had later been retracted or disputed. Physicist Guy Wilkinson, then LHCb's spokesperson, called it 'a new way of studying the strong force' that binds ordinary matter together.
The pentaquark result mattered less as a shock discovery and more as confirmation of the flexibility of quantum chromodynamics, the theory governing the strong nuclear force. It opened new avenues for probing exotic matter states, and subsequent LHC runs have since identified additional pentaquark and tetraquark particles, enriching the periodic-table-like landscape of hadronic matter.
Key people: Guy Wilkinson