An inn of four quarks challenges physics and physicists
An inn of four quarks defies physics and physicists
The physicists of the Belle experiment of the KEK Laboratory in Japan discovered a curious inn named Z (4430). According to some, it would be a particle composed of four quarks.
The physicists of the Belle experiment of the KEK laboratory in Japan discovered a curious inn named Z (4430). According to some, it would be a particle composed of four quarks. Such a thing seems impossible or almost within the framework of the theory of quantum chromodynamics.
Since their introduction into the world of particle physics in the early 1960s by Gell-Mann, Ne’eman and Zweig, quarks have not ceased to intrigue physicists for their abnormal behavior with respect to other elementary particles. However, the theory of strong interactions that dominated the world of hadrons built with them, was particularly perfect for describing experiments on accelerators.
However, the equations of the QCD (quantum chromodynamics) that describe the exchanges of gluons between quarks, and are responsible for the composite structure of protons and neutrons, are notoriously difficult to solve because of their nonlinear structure. What does not always understand very well why quarks are confined in hadrons, although much progress has been made since the late 1960s, it is almost always impossible to predict the mass of protons and neutrons without using computers.
In spite of everything, the theory implies quite solidly that quarks can be joined only by pairs of particle-antiparticle, to form mesons, and by three to form barions.
It was therefore with some surprise that the experimenters engaged in analyzing the products of the collision reactions between electrons and positrons, with the BaBar experiment of the Stanford Linear Accelerator Center and Belle in the KEK Laboratory, discovered important indicators of the presence of mesons constituted by Four quarks
An excited state of charmonium?
At first, this did not seem the most plausible explanation. Indeed, inns, such as barons, being composed of atoms, have energy levels and can be in an excited state. The first hypothesis presented was that precisely in the presence of this phenomenon with a meson at rest and still called charmonium because it is composed of a quark at rest and an antiquark at rest (rest designates a quantum state analogous to spin for this type of quark), we find it just in the state of disintegration of one of the unstable inns that could be interpreted as constituted by 4 quarks.
It happens then, that the méson Z (4430) discovered today is charged while the charmonium is neutral! It seems difficult to believe that it is a state of excitement. Also, Z (4430) disintegrates in charmonium and in an inn? (PI) loaded. We are thus in the presence of a meson candidate with four quarks that seem very discernible from an excited state of the charmonium unlike the other inn: the X (3872).
Not all physicists are still convinced and some think that new experiments are still necessary. Indeed, if the existence of a meson with four quarks were confirmed, the QCD equations would have to be reexamined, if not the theory of strong nuclear interactions itself.
To know more
In particle physics, an inn(from ancient Greek ????? (Mesos) = medium) is a boson that responds to the strong interaction, that is, a hadron with a whole spin. In the standard model, inns are particles composed of an even number of quarks and antiquarks. It is believed that all known mesons consist of a quark-antiquark pair, the so-called quarks of Valencia, plus a “sea” of quark-antiquark pairs and virtual gluons. The search for exotic inns that have different constituents is in progress. Valencia quarks may exist in a superposition of states of taste (physical); for example, the neutral pion is neither an up-anti-upset nor a down-anti-low pair, but an equal quantum overlap of both. Pseudoscalar mesons (with spin 0) have the lowest resting energy, where the quark and antiquark have opposite spins, and then the vector inn (with spin 1), where the quark and antiquark have parallel spins. Both come in higher energy versions where the spin is increased by the orbital angular momentum. All inns are unstable.
The inns were originally predicted as carriers of the force that binds the proton and the neutron, hence their name. When it changed into discovered, the muon recognized with this circle of relatives of similar mass and became baptized as a “mu inn”, however it did not show a sturdy attraction to nuclear count and is truely a lepton.
The pion was the first true inn to be discovered.
In 1949 Hideki Yukawa was awarded the Nobel Prize in physics for predicting the existence of the inn. I originally call it “mesotron”, but it was corrected by Werner Heisenberg (his father was a professor in Greek from the University of Munich), who indicated that there was no “tr” in the Greek word “mesos”.