Only a year ago, Peter Higgs, François Englert and received the Nobel Prize for his work, which was devoted to the study of subatomic particles.This may seem absurd, but their discoveries scientists have made half a century ago, but to this day they did not give though a little matter.
In 1964, two talented physics also played with his ground-breaking theory.At first, she also attracted little attention.It's strange, because she described the structure of hadrons, which are indispensable for any one strong interatomic interaction.This was the theory of quarks.
What is it?
By the way, what is a quark?This is one of the major components of the hadron.Important!This particle has a "half" spin, actually being a fermion.Depending on the color (see below) quark charge may be equal to one-third or two-thirds of the proton charge.As for colors, they number six (generation of quarks).They are necessary in order not to violate the principle of Pauli.
Basics
As part of hadrons, these particles are at a distance not exceeding the value of the confinement.The reason is simple: they exchange vectors gauge field, ie the gluons.Why is it so important quark?Gluon plasma (saturated quarks) - a state of matter in which the whole universe was just after the Big Bang.Accordingly, the existence of quarks and gluons - a direct confirmation that it really was.
They also have a different color, but because of the movement to create their virtual copies.Accordingly, when the distance between the quarks force between them increases significantly.As you might guess, with a minimum distance of interaction practically disappears (asymptotic freedom).
Thus, any strong interaction in hadrons is due to the transition of gluons between quarks.If we talk about interactions between hadrons, they are explained by the transfer of pi-meson resonance.Simply put, all indirectly again reduced to the exchange of gluons.
How quark part of the nucleon?
Each neutron consists of a pair of d-quarks, and the exact same single u-quark.Each proton, on the contrary - from a single d-quark and a pair of u-quark.By the way speaking, the letters are placed depending on the quantum numbers.
explain.For example, beta decay is explained by just the same transformation of one of the same type as part of the nucleon quark into another.To be better understood as a formula this process can be written this way: d = u + w (a neutron decay).Accordingly, the proton is written slightly different formula: u = d + w.
Incidentally, this latter process is explained by a steady stream of neutrinos and positrons of the major star clusters.So the scale of the universe is so important little particles, which is a quark-gluon plasma, as we have already said, confirms the big bang, and the study of these particles allow scientists to learn more about the essence of the world in which we live.
With less than a quark?
By the way, what it consists of quarks?They are part and parcel preons.These particles are very small and poorly understood, so that even today they are known not so much.That is less than a quark.
Where did they come from?
Today, the most common form preons two hypotheses: string theory and the theory of Bilson-Thompson.In the first case, the occurrence of the particles is explained string oscillation.The second hypothesis suggests that their appearance is due to an excited state of space and time.
interesting that in the second case it is possible to describe the phenomenon, using a matrix of parallel transport along curves of the spin network.The properties of the matrix itself, and to determine any preons.That is what constitutes the quarks.
Summing up, we can say that the quarks - a kind of "quanta" as part of hadrons.Impressed?And now we will talk about how to do was open the quark.This is a very exciting story that, among other things, fully disclose some details described above.
Strange particles
Immediately after the end of World War II, scientists began to actively explore the world of subatomic particles, which until then seemed to just primitive (for the view).Protons, neutrons (nucleons) and the electrons formed atom.In 1947 he opened peonies (and predicted their existence in 1935), who were responsible for the mutual attraction of nucleons in the nucleus of atoms.This event was in its time was devoted not one scientific exhibition.Quarks were not yet open, but the time of the attack on their "footprint" was getting closer.
Neutrinos at the time had not yet been discovered.But their sheer importance to explain the beta decay of atoms was so great that scientists have little doubt their existence.In addition, already detect or predict some antiparticles.Once the situation was unclear with muons, which are formed by the decay of pions and later passed into the state of neutrinos, electron or positron.Physicists do not understand, why do I need this intermediate station.
Alas, so simple and unpretentious model very briefly survived the opening of the pions.In 1947, two British physicist, George Rochester and Clifford Butler, published a curious article in the scientific magazine Nature.The material for it was the study of cosmic rays through the cloud chamber, in which they got very curious information.On one of the photos captured during the observation, it was clearly visible a couple of tracks with a common origin.Since the difference was like a Latin V, then it became clear - charge these particles are definitely different.
Scientists once assumed that these tracks indicate the fact of the collapse of some unknown particle that is not left behind other tracks.Calculations showed that its weight - about 500 MeV, which is much greater than this value for the electron.Of course, researchers have named their discovery V-particle.However, this was not the quark.This particle was still waiting in the wings.
Everything is just beginning
With this discovery it began.In 1949, under the same conditions it was found trace particles, which gave rise immediately to three pions.It soon became clear that she, as well as and V-particle - totally different members of the family, consisting of four particles.Later they were called K mesons (kaons).
Couple charged kaons have a mass 494 MeV, and in the case of neutral charge - 498 MeV.Incidentally, in 1947, researchers lucky enough to capture just the same very rare case of a positive kaon decay, but at the time they just were not able to correctly interpret the picture.However, to be perfectly fair, it is in fact the first observation of the kaon was made back in 1943, but information about it was almost lost against the background of the many post-war scientific publications.
New strangeness
And then scientists waited more discoveries.In 1950 and 1951, researchers from the universities of Manchester and Melnburskogo managed to find a particle is much heavier than protons and neutrons.Again, she had no charge, but decays into a proton and a pion.The latter, as can be understood, has a negative charge.New particle denoted by the letter Λ (lambda).
The more time passes, the more the question arises scientists.The problem was that the new particles are produced solely in strong nuclear interactions, rapidly breaking down to form protons and neutrons.In addition, they always appear in pairs, the single manifestation was never.And so a group of physicists from the US and Japan proposed to use in their description of a new quantum number - strange.According to their definition, the strangeness of all other known particles was zero.
Further research
breakthrough occurred only after the investigations of a new systematization of hadrons.A prominent figure in the Israeli Yuval Ne'eman became that changed the outstanding military career at an equally brilliant way of a scientist.
He noted that the open by the time the mesons and baryons fall, forming a cluster of related particle multiplets.Members of each of these associations have exactly the same strangeness, but opposite electric charges.So how did the strong nuclear interaction of electric charges do not depend at all, in everything else particles of a multiplet look perfect twins.
Scientists have suggested that the occurrence of these natural formations meets certain symmetry, and soon they were able to find her.She was a simple generalization of the spin group SU (2), which scientists around the world use to describe the quantum numbers.That's just at that time was already known hadron 23, and their backs were equal to 0, ½ or a whole unit, therefore use a classification not possible.
As a result, we had to use for the classification just two quantum numbers, due to which the classification has expanded considerably.So there was a group of SU (3), which at the beginning of the century has created a French mathematician Elie Cartan.To determine the taxonomic position in it of each particle, the scientists developed a research program.Quark then easily entered into a systematic series, which confirmed the absolute correctness of specialists.
new quantum numbers
So scientists have come to the idea of using abstract quantum numbers, which have become hyper- and isotopic spin.However, with the same success can take strange and electric charge.This scheme has been provisionally named the Eightfold Path.This is captured analogy with Buddhism, where until Nirvana also need to go through eight levels.However, all this poetry.
Ne'eman His work and his colleague, Gell-Mann, published in 1961, and the amount of the then known mesons did not exceed seven.But in their paper, the researchers did not hesitate to mention the high probability of the existence of the eighth meson.Also in 1961 their theory brilliantly confirmed.Found this particle called mesons (Greek letter η).
Further discoveries and experiments brilliantly confirmed the absolute correctness of the classification of the SU (3).This became a powerful incentive to researchers who have found that there are on the right track.Even the Gell-Mann had no doubt that in nature there are quarks.Reviews of his theories were not very positive, but the scientist was sure that he was right.
Here and quarks!
soon published an article "A schematic model of baryons and mesons."In it, scientists were able to further develop the idea of organizing, which was so helpful.They found that the SU (3) readily admits the existence of whole triplets of fermions, the electric charge which ranges from 2/3 to 1/3 and 1/3, and in the triplet one particle is always different non-zero strangeness.Already well-known Gell-Mann, we called them "elementary particles quarks."
According to the charges, he labeled them as u, d and s (from the English words up, down, and strange).Under the new scheme, each baryon formed by three quarks.Mesons are arranged much easier.They contain one quark (this rule is firm) and an antiquark.Only after that the scientific community has become aware of the existence of these particles, which are dedicated to our article.
A little history
This article, which is largely determined the development of physics in the years ahead, has a rather interesting history.Gell-Mann thought of the existence of such triplets long before its publication, but no one to discuss their assumptions.The fact that his assumptions about the existence of particles having a fractional charge looked as delusions.However, after a conversation with an outstanding theoretical physicist Robert Serber he learned that his colleague did exactly the same conclusions.
In addition, the scientist made the only correct conclusion that the existence of such particles is only possible if they are not free fermions, as part of hadrons.Indeed, in this case, their charges are integrated!First of Gell-Mann called them kvorkami even mentioned them in MTI, but the reaction of students and teachers was very low-key.So a scientist for a long time thinking about whether he should make his research to the public.
word "quark" (this sound like the cry of the ducks) was taken from the works of James Joyce.Oddly enough, but the American scientist has posted an article in the prestigious European scientific journal Physics Letters, because seriously feared that a similar revision in terms of the American edition of Physical Review Letters will not accept it for publication.By the way, if you want to look at least a copy of the article - you direct road to the same Berlin museum.Quarks in his exposition is not available, but the full story of their discovery (or rather, documentary evidence) is.
Home quark revolution
fair to say that almost at the same time to the same thought came from CERN scientist, George Zweig.At first, his mentor himself was Gell-Mann, and then Richard Feynman.Zweig also defined the reality of fermions, which had fractional charges, but called them aces.Moreover, a talented physicist, also considered as the three quark baryons and mesons - as a combination of a quark and an antiquark.
Simply put, the student is fully repeated the conclusions of his teacher, and completely separate from it.His work has appeared even a few weeks before the publication of Mann, but only as a "home-made" Institute.However, it is the presence of two independent papers, the conclusions of which were almost identical, once convinced some scientists allegiance to the proposed theory.
From rejection to trust
But many researchers have taken this theory is not right.Yes, journalists and theorists quickly fell in love with her for clarity and simplicity, but serious physics took it only after as long as 12 years.You should not blame them for excessive conservatism.The fact that the original theory of quarks in sharp contrast to the Pauli principle, which we mentioned at the beginning of this article.If we assume that the proton contained a pair of u-quarks and one d-quark, the first should be strictly in the same quantum state.According to the Pauli it is impossible.
It was then and there was an additional quantum number, expressed as a color (as we mentioned above).In addition, it is unclear how all elementary particles quarks interact with each other, why not meet them free varieties.All these greatly helped unravel the mysteries of the gauge field theory, which "brought to mind" only in the mid 70s.Around the same time, the quark theory of hadrons organically incorporated into it.
But most strongly hampered the development of the theory of the complete absence of at least some of the experimental tests that would confirm the existence of both, and the interaction between quarks and other particles.But they gradually began to appear only at the end of the 60s, when the rapid development of technology allowed for the experience of a "transmission" electron beams of protons.It is these experiences have allowed to prove that inside protons really "hide" some particles, which was originally called partons.Later still convinced that it is nothing like a true quark, but it was only in late 1972.
Experimental confirmation
Of course, the final conviction of the scientific community took a much more experimental data.In 1964, James Sheldon Glashow and Bjorken (future Nobel Prize winner, by the way) have suggested, though there may be a fourth species of quark, which they called a charmed (charmed).
It is thanks to this hypothesis, researchers in 1970 were able to explain many oddities that have been observed in the decay of neutral kaons charged.Four years later, just two independent group of American physicists were able to fix the meson decay, which included just one "charmed" quark and its antiquark.It is not surprising that this event once dubbed the November Revolution.The theory of quarks get more or less "visual" confirmation.
about the importance of the opening of said at least the fact that the project manager, Samuel Ting and Burton Richter, two years later received a Nobel Prize: An event is reflected in many articles.
