Antibaryonic

Like the leptons, there is a number conservation law for baryons. To each baryon, such as the neutron or proton, we assign a baryon number B = +1 while we assign B = — 1 to each antibaryon, such as the antiproton. Our rule is that the total baryon number must be conserved in any process. Consider the reaction... 

There is another alternative to SBBN which, although currently less favored, does have a venerable history BBN in the presence of a background of degenerate neutrinos. First, a brief diversion to provide some perspective. In the very early universe there were a large number of particle-antiparticle pairs of all kinds. As the baryon-antibaryon pairs... 

Density of baryons energy of Is state in antibaryon potential (MeV) number of bound particles... 

In high energy heavy ion collisions it might be possible to produce antimatter clusters like d, He, etc. out of the highly correlated vacuum in contrast to their conventional production by fusing antibaryons, step by step, in phase space. 

There is also the possibility of obtaining overcritical baryonic potentials. In this case the possibility of spontaneous baryon-antibaryon pair creation occurs. This process is, however perhaps less relevant in heavy encounters because of the short time scale for the overcritical situations (short time scale of the over-critical compression). 

Many observable signals proposed for the quark-gluon plasma, in particular enhanced antibaryon yields may be interpreted in the purely hadronic scenario, if the reduction of hadron masses at high density is taken into account[30]. 

Inflation also distorts the mass budget of the universe so badly that less than 1% of the total mass appears visible, but this is the total mass that neatly balances the large-number coincidences of the anthropic principle. The excess must therefore be non-baryonic matter, for which there is no evidence. At the same time, the equal mass of antibaryons, implied by CPT symmetry, is declared non-existent. Antileptons are simply ignored. 

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. 

FIGURE 8.30 The left panel shows the sum of proton and neutron densities (top) as well as the corresponding sum for antibaryons for the a-a system. The right panels shows the scalar potentials and the single particles levels of the nucleons and antinucleons. 

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... 

Ap is simply Ap/piab- For piab = 10 GeV and Ap = 0.4 GeV this gives 0.04. Assuming the geometrical fraction of central events 20% we get the final estimate W 0.17x0.04x0.2 1.410 . One should bear in mind that additional reduction factors may come from the matrix element between the bare massive antibaryon and the dressed almost massless antibaryon in a deeply bound state. But even with extra factors 10 -10 which may come from the detailed calculations the detection of SBNs is well within the modern experimental possibilities. 

It is interesting to look at the antibaryon-nucleus system from somewhat different point of view. An antibaryon implanted into a nucleus acts as an attractor for surroimding nucleons. Due to the uncompensated attractive force these nucleons acquire acceleration towards the center. As the result of this inward collective motion the nucleons pile up producing local compression. If this process would be completely elastic it would generate monopole-like oscillations around the compressed SBN state. The maximum compression is reached when the attractive... 

The admixture of antibaryons to finite nuclei provides an almost unique doorway to the study of cold compressed nuclear and/or quark matter in the laboratory. This region of the phase diagram of strongly interacting matter, see Figure 8.31, is not accessible by collisions of heavy ions, which produce matter which is simultaneously hot and dense. 

It is clear however that these structural changes can occur only if the life time of the antibaryons in the nuclear interior is long enough. 

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). 

The elementary interactions violate the baryon-antibaryon symmetry. 

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

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. 

Baryons have baryon number +1. Antibaryons have baryon number—1. Both have lepton number 0. 

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