Hadrons

"Just as elephants live together in groups, quarks also only exist in groups with other quarks. They never occur alone. Quarks make up particles we call hadrons".

Hadrons (Greek hadros = strong, exuberant) are subatomic particles. Their main characteristic is the strong nuclear interaction. Currently, hadrons are no longer considered elementary particles. They are characterized as objects composed of quarks. Known hadrons are divided into baryons and mesons.

Properties

• Hadrons can be either bosons (then they are mesons) or fermions (then they are baryons).
• They respond to strong interaction.
• They are always color neutral , because their color charge is zero.
• Each hadron also has its own antiparticle, which is assembled from the corresponding antiquarians.
• Apart from the proton, we classify all hadrons as unstable particles.
  • An interesting group are - metastable particles. Only a weak or electromagnetic interaction is sufficient to disintegrate these particles.

• Resonance – excited state of a hadron.

Baryon

The baryon octet

The term is derived from the Greek "barys", meaning "heavy", which is related to the fact that baryons have a higher rest mass than other particles.

Baryons can be divided into lighter ones – nucleons, which include protons and neutrons containing quarks ( u, d ) and heavier ones – hyperons, which include Λ hyperon, Σ hyperons, Ξ hyperons and Ω hyperon, containing quark ( s ).

Baryons are composed of three quarks , which can be combined - see Fig. baryon octet:

• The I3 axis expresses the isospin magnitude of individual baryons; it can reach values ​​from -1 to 1, but let's not confuse it with the spin of individual baryons - it can only be semi-numerical, i.e. 1/2, 3/2,...;
• The Q axis expresses the charge of baryons and in the figure reaches the values ​​-1, 0, 1;
• S is the so-called axis of strangeness and in the figure it reaches the values ​​0, 1, 2. The composition of individual baryons from quarks u, d, s is shown in the pink points of the diagram.

All baryons have a mass equal to or greater than the mass of a proton.

   $m_{p}=1,6726231\times 10^{-27}kg$                                        

Mesons

Meson nonet

Mesons have zero or integer spin, which simultaneously ranks them among bosons. They are composed of a quark and an antiquark , have a very short lifetime and are color neutral particles.

Their composition is indicated in Fig. meson nonet.

• The I3 axis again determines the value of the isospin and in the figure it reaches the values ​​−1, −1/2, 0, 1/2, 1. The resulting spin of the mesons is either zero or an integer. S is the axis expressing the "strangeness" value and is given by where n is the number of quarks and antiquarks, which explains the curious fact that antiquark-containing mesons have s = +1.

    $S=-(n_{s}-n_{antis})$

• In the picture, we can also imagine the Q axis , which would be located the same as in the previous picture and would reach the values ​​−1, 0, 1.

We divide mesons according to the mutual orientation of the spins:

• scalar mesons – the spin of the quark is oriented opposite to the spin of the antiquark, the resulting meson spin is zero s = 0 ;
• vector mesons – the spin quark and antiquark have the same direction, the resulting meson spin is s = 1.

For mesons with a higher resulting integer spin, the spins of the quarks also add up to the orbital angular momentum. Unlike baryons, we cannot talk about antimatter with mesons, because the antiparticle of a meson is a particle in which the quark from the original meson is replaced by the corresponding antiquark and the original antiquark by the corresponding quark, so the resulting particle is again a meson.

History

In 1947, the meson π (pion) was discovered in cosmic rays. Subsequently, K mesons were discovered in the early 1950s. During the 1950s and 1960s, more hadrons were discovered at accelerators. The 1970s saw the discovery of two new classes of hadrons that contain additional types of quarks, the ( c and b ) quarks.

The use of hadrons in medicine - hadron therapy

It is the irradiation of tumor structures, which uses heavy charged particles belonging to hadrons (protons - belonging to the lightest baryons and π mesons). Unlike light particles ( photon and electron ), which transfer a large part of their energy when they collide with another electron, or completely change their direction of flight, heavy hadrons transfer only a small part of their energy during collisions and their direction of flight changes only minimally. Thus, hadrons lose their energy gradually when passing through tissues, and therefore do not scatter and all arrive at approximately the same place. The faster a particle flies, the less energy it loses along the way. The direction of particle flight can be corrected usingmagnetic field, and thus the location of hadron impact can be determined very precisely. The tumor is then very precisely destroyed without major interventions in the surrounding tissue.

Irradiation using hadrons has been known since 1954. However, the hadron accelerator, which is a necessary but very expensive part of such a device, remains an unsolved problem. Additionally, this radiation is suitable for approximately 5-10% of cancer patients. The tumor is deep and well localized. Most often, therefore, brain tumors, where it is especially important to remove the tumor without the slightest damage to the surrounding healthy tissue.

See the Proton therapy page for more detailed information .

Resources

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• UNKNOWN, Author. Hadrons, Baryons  [online]. [feeling. 2013-11-28]. < https://cs.wikipedia.org/wiki/Baryon , https://cs.wikipedia.org/wiki/Hadron >.

• RAMES, Jiří. Hadrons  [online]. [feeling. 2013-11-28]. < http://www-hep2.fzu.cz/adventure/hadrons.html >.

• HOREJŠÍ, Jiří. Hadrons  [online]. [feeling. 2013-11-28]. < http://www-ucjf.troja.mff.cuni.cz/~horejsi/popular/hadrony.html >.

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