Quarks are a type of elementary particle and a basic constituent of matter. There are six types of quarks with a wide range of masses: up, down, charm, strange, and top and bottom. They usually combine in groups of two/three to form hadrons, like protons and neutrons.
Recently, the LHCb international collaboration at the Large Hadron Collider (LHC) observed three never-before-seen particles: a new type of “pentaquark” and the first pair of “tetraquarks” that includes a new type of tetraquark.
The first kind is a pentaquark composed of an up, down, strange quark and a charm quark, a charm antiquark and observed in an analysis of the “decay” of negatively charged B mesons. It is the first discovered pentaquark that has a strange quark. The result was statistically significant at a staggering 15 standard deviations, far higher than the five standard deviations needed to declare the discovery of a particle in particle physics.
The second type is a tetraquark with two electric charges. It is an open charm tetraquark with an up quark, a down quark, a strange antiquark, and a charm quark. Its neutral counterpart is a joint study of the decay of positively charged and neutral B mesons. This is the first time a tetraquark pair has been seen, and the new tetraquarks were detected with a statistical significance of 6.5 (a doubly charged particle) and 8 (a neutral particle) standard deviations.
LHCb physics coordinator Niels Tuning said: “The more analyzes we do, the more types of exotic hadrons we find. We are witnessing a period of discovery similar to that of the 1950s, when a “particle zoo” of hadrons began to be discovered and eventually led to the quark model of conventional hadrons in the 1960s. We are creating a “Particle Zoo 2.0”.
LHCb spokesman Chris Parkes said: “Finding new types of tetraquarks and pentaquarks and measuring their properties will help theorists develop a unified model of exotic hadrons, whose exact nature is largely unknown. It will also help to better understand conventional hadrons.
The findings, presented today at a workshop at CERN, add three new exotic members to the growing list of new hadrons discovered at the LHC.
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