Scientists have declared the reality of exotic tetraquarks.
Two independent groups of physicists discovered new exotic elementary particles - tetraquarks “at the tip of a feather” in different ways. Scientists have come to the conclusion that they can exist on a stable basis, although only particles with no more than three quarks are known in the nature around us. Potentially, tetraquarks can exhibit properties that have not yet been demonstrated by “ordinary” elementary particles previously known to science. Related articles are published in Physical Review Letters.
All the bodies we observe consist of hadrons - elementary particles subject to strong nuclear interaction, which holds together those particles of which we ourselves are composed. The most famous subclass of hadrons is baryons, namely protons and neutrons, of which the nuclei of all atoms are composed (and all molecules, planets, stars and living things consist of atoms).
Baryons familiar to us consist of three quarks [qqq], special particles with a fractional electric charge (2/3 or -1/3) and do not exist in a free form, but only in the composition of baryons. However, the calculations of theorists have shown long ago that nothing prevents the existence of tetraquarks, for example, as particles in which there are three quarks and one antiquark [qqq¯q¯]. The fact that they have not yet been found in nature was attributed to the extreme instability of such tetraquarks. It was assumed that their mass is so great that they quickly decay through a strong interaction, in contrast to ordinary hadrons (the same baryons), decaying through a weak nuclear interaction, and therefore exist much longer.
The authors of both new works carried out calculations of the stability of the existence of particles consisting of four quarks, in which there are two quarks and two antiquarks. This approach differs from the previously assumed models, where there were three quarks and one antiquark in a tetraquark (a particle in everything similar to a quark, but with an opposite charge). They managed to find out that its mass is 10 389 MeV / s2 (megaelectronvolt at the speed of light squared - in elementary particle physics, instead of mass, in accordance with Einstein's E = mc2, its energy equivalent is used). This is noticeably less than the lightest combination of baryons and mesons with corresponding characteristics. From which it follows that such a tetraquark-hadron will be as stable as the typical baryons that surround us.
New calculations show that four-quark particles must exist long enough to be detected experimentally. The question arises, why does this not happen in practice? Possible answers to this question include the short lifetime of tetraquark particles. However, if they are obtained in the laboratory, it is quite possible to study their properties, which should differ markedly from those of ordinary three- and two-quark particles.
IVAN ORTEGA