On 9 April 2014, researchers at the LHCb experiment published a paper validating the existence of an exotic particle, which appears to be a tetraquark. The LHCb spokesperson Pierluigi Campana said: “We are very happy to have confirmed this particle, which is in fact a very strange object.”
Precisely 50 years ago, George Zweig and Murray Gell-Mann independently introduced the Quark Model, which is a fundamental cornerstone in particle physics. The model is a perfect tool to understand how matter interacts especially when describing the history of the universe.
So far, the theory described particles made up of a quark and an anti-quark (mesons) and particles comprising 3 quarks (baryon). At the beginning of the 21st century, the BaBar and Belle experiments provided hints regarding exotic particles formed from 4 quarks, called tetraquarks. “We have suspected all along that the strong interaction should in principle be able to do this, but this is the first time that we have indisputable proof that nature can form an object with 4 quarks together,” said LHCb physicist Richard Jacobsson.
The LHCb Collaboration at CERN studied decay processes and the current scheme based on meson and baryon could not explain the results. The mass distribution confirmed the Belle Collaboration observation: the particle called Z(4430) is a tetraquark, which is either a four quark state or a two-quark plus two-antiquark state.
This object belongs to the first microseconds of the beginning of the universe. However interactions, which cause the existence of tetraquarks, still affect the matter now. Investigating the particle physics will help in the global understanding of matter.
The paper entitled ‘Observation of the resonant character of the Z(4430)− state‘ can be found on ArXiv.