A tetraquark particle, a form of matter rarely seen by human beings, has been created at the Large Hadron Collider, the world's largest particle accelerator, located outside of Geneva, Switzerland.
Atomic theory in the 1930s had determined atoms were composed of a core containing positively-charged protons and neutrons, which have no charge. Surrounding this nucleus, a cloud of electrons carry a negative electric charge. Put together, most atoms are electrically neutral.
Additional subatomic particles were discovered in the 1950s, which led physicists to again question the underlying nature of matter.
Murray Gell-Mann, a physicist known for his remarkable insights, developed his theory of quarks, three of which were said to make up each proton or neutron. These particles were confirmed by experiments carried out in the 1960s. Gell-Mann named the particle after a line from "Finnegan's Wake" by James Joyce.
The quark model has proven highly successful in predicting the results of experiments. Protons and neutrons, made up from three quarks, are classified as baryons. Members of this group are also part of a larger group of particles, called hadrons, which also include mesons, composed of two quarks.
"In the traditional quark model, the strongly interacting particles (hadrons) are formed either from quark-antiquark pairs (mesons) or three quarks (baryons). Particle physicists were searching since 50 years for the particles, called exotic hadrons, which could not be classified within this scheme. Many candidates have been proposed but up to now there has not been unambiguous proof of their existence," researchers reported in a press release announcing the discovery.
Discovery of the exotic Z(4430)- particle was first announced by researchers at the Belle Collaboration in Japan in 2007. The experiment at the LHC confirms this finding.
The tetraquark appears to be made from four quarks, unlike any confirmed form of matter known to mankind. Over the past few decades, candidate particles have been found, but none has yet been verified.
Quarks come in six varieties, whimsically named up, down, top, bottom, strange and charmed. Each particle also has an anti-matter counterpart. Mesons are formed by pairings between a quark and its anti-matter twin.
The tetraquark particle is likely made up from a charm, anti-charm, anti-up and down quark, according to researchers who made the discovery.
The Large Hadron Collider is operated by the European Organization for Nuclear Research (CERN).
After witnessing the decay of 25,000 mesons caused by 180 trillion subatomic collisions, existence of the new tetraquark particle is being announced with a confidence of 13.9 sigma. That is a far higher level than the five-sigma level usually considered to constitute proof.
