Baryons and Antibaryons

It is interesting to consider finite systems having total baryon number zero, i.e. systems with the same amount of baryons and antibaryons. In the following we will present the cases of an o -anti-o and an O-anti- O system. Figure 8.30 shows the... 

On the interface of neighboring domains of baryonic and antibaryonic matter, quark—antiquark (proton-antiproton) annihilation would lead to the emission of hard X-rays. The absence of this signal makes it highly probable that even if antibaryons were present in the early, hot Universe they had disappeared before the CMBR was emitted. Therefore, the observed baryonic density actually proves the presence of a matter—antimatter asymmetry within the present horizon in our Universe (Rubakov and Shaposhnikov 1996 Riotto and Trodden 1999). 

There is also conservation of the baryon number in every reaction. The baryons have baryon number -fl and the antibaryons have baryon number —1 all other particles have baryon number 0. In the various processes of formation of baryons and antibaryons they are always formed in pairs, one baryon and one antibaryon. Similarly, the decomposition of a baryon always leads to the formation of another baryon, plus other particles with 0 baryon number. Thus the negative xi particle is observed to decompose to form a lambda particle, which has baryon number +1, and a negative pion, which has baryon number 0. 

The baryons include the nucleons and heavier particles. Eight baryons and eight antibaryons are listed in Table 20-3. The word baryon is from the Greek baiys, heavy. The word hyperon (Greek hyper, beyond) is also used it refers to the baryons other than the proton and the neutron. 

FIGURE 8.23 Due to the high temperature and the violent dynamics, many bound holes (antinucleon clusters) are created in the highly correlated vacuum, which can be set free during the expansion stage into the lower continuum. In this way, antimatter clusters can be produced directly from the vacuum. The horizontal arrow in the lower part of the figure denotes the spontaneous creation of baryon-antibaryon pairs, while the antibaryons occupy bound states in the lower potential well. Such a situation, where the lower potential well reaches into the upper continuum, is called supercritical. 

The baryons, antibaryons, leptons, and antileptons are all fermions. Particles with spins f, t,. . . are also fermions. 

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