Physicists have found evidence for the existence of tetraquarks
Physicists have discovered new evidence for the existence of tetraquarks, hypothetical particles made up of two quarks and two antiquarks. The scientists published their arguments in the journal Physical Review Letters.
Quarks are elementary particles with a fractional electric charge; they are made up of particles called hadrons. The latter, in particular, include protons, neutrons and mesons. Quarks do not occur in a free form, so scientists have to study their characteristics using indirect experiments.
Quarks combine with each other in a non-random way. At the moment, physicists know several possible combinations of quarks, each of which corresponds to a specific hadron. However, it is possible that other combinations of quarks may exist in nature. One such potential combination is two quarks and two antiquarks. The particle containing this combination was named a tetraquark.
The authors of the new work suggested that the existence of tert-quarks can best explain the unusual experimental data obtained during experiments at the KEKB electron-positron collider located in Japan. Scientists working at KEKB collide electrons with their oppositely charged “antipodes” – positrons. Collisions can form new particles that decay very quickly. Researchers judge the nature of the particles produced by the decay products.
In 2008, physicists investigated the decays of the excited state of the Y (5S) upsilon meson. Existing theories predict that such decays will very rarely lead to the appearance of less excited states – Y (1S) or Y (2S) – and a pair of charged pi-mesons, but the detectors recorded a very significant number of these events.
The authors of the new work suggested that the unusually high number of “incorrect” decays is due to the fact that collisions produce not only Y (5S) upsilon mesons, but also Y tetraquarksb(10890), the decay of which gives the above particles. The researchers performed the appropriate calculations, and the resulting data were in good agreement with the experimental data.
Not all of their colleagues agree with the conclusions of physicists. Opponents point out that the unusual characteristics of the decays can be explained by the yet unexplored properties of Y (5S) upsilon mesons. In order to find out how legitimate the statement about the existence of tetraquarks, scientists intend to carry out a number of experiments in the near future and see if their results coincide with theoretically predicted ones.