Neutral pions

The theory outlined above is adequate for the description of a system of noninteracting bosons of mass m and spin 0 that are electrically neutral and that have no other quantum numbers to characterize them, for example, the neutral pions. It is, however, observed in nature that for particles with spin 0 that do have other quantum numbers specifying them, such as charge and strangeness, there always exist two kinds of particles with the same mass and spin but opposite additive quantum numbers such as charge and strangeness. By additive we mean that the quantum number for a system of such particles is the algebraic sum of the quantum numbers for the individual particles. 

The latter situation is similar to the neutral pion condensation in nuclear matter. 

The baseline calculation is to assume that the intensity observed locally at Earth is representative of the distribution everywhere in the disk of the galaxy. One can then look for interesting variation superimposed on this baseline. Following the analysis of Eqs. [9,10,11,12], the average number of neutral pions produced per GeV per unit volume in the interstellar medium is... 

Following a leptonic model, gamma rays may arise from inverse Compton (IC) processes when the relativistic electrons of the jet interact with external photons from the massive companion star. If the jets are hadronic, the gamma rays may come from the decay of neutral pions in the interaction between protons from the jet and ions from the wind of the companion star. 

It is likely that the metallicity of at least the larger galaxies will increase steadily during the next 10 years because of the productivity of supernovae but nevertheless remaining far removed from the favored thermodynamic equilibrium of iron and adjacent elements (cf. Table 1). However, we have had more than the usual ration for a millenium of revolutions in physics and astronomy since 1887. Contrary to the 30 or 100 Lavoisier elements, it is an ancient trend in chemistry [5] to look for unity in matter [a thought that was not alien to Sir Isaac Newton (1642-1727)]. Before 1934 Dirac convinced physicists that all fermions and most bosons (except photons, neutral pions, and a few unusual... 

Quantum mechanics has to a large extent resolved an antinomy inherited from the discussions of Heraclit and Democrit. The wave-functions are continuous and extended in the former sense, but at the same time, the indivisible parts of Democrit have been replaced by normalization conditions, the numbers K, Z, N,.. . of electrons, protons, neutrons,.. . being cardinal numbers without any possible way of assigning ordinal numbers to the individual, indiscernible entities. This trend has been further accentuated by most particles having anti-particles, with exception of some bosons (such as the photon and the neutral pion, but not the a-particle). 

Experimentally, the two-photon decay of neutral pions from the charge-exchange reaction following n capture in proton ... 

The ECAL barrel has a volume of 8.14 m and its front face is at a radial distance of 1.29 m from the interaction point. It has a 360-fold azimuthal segmentation and two times 85-fold segmentation in pseudorapidity. The endcap has a coverage of 1.479 < 7l < 3 and is situated at a longitudinal distance of 3.15 m from the interaction point. A preshower detector with a thickness of 3 Xq is placed in front of the endcaps (1.653 < rj < 2.6) to guarantee a reliable discrimination of single photons and photons produced in pairs in neutral pion decays. 

The known mesons and antimesons, eight in number, are listed in Table 20-2. The kaons are the antiparticles of the antikaons, and the two charged pions are antiparticles of one another. The neutral pion is its own antiparticle, and the eta particle is its own antiparticle. All of the mesons are unstable their decay reactions will be discussed in Section 20-8. 

The principle of conservation of electric charge is illustrated by the decay reactions given in Table 20-4. For example, the lambda particle, which is a hyperon, with mass somewhat greater than that of a nucleon, can decompose either to form a proton and a negative pion or to form a neutron and a neutral pion. In the first case the lambda particle, which is neutral, forms a positively charged particle and a negatively charged particle in the second case it forms two neutral particles. 

During his pioneering work on the foundations of quantum mechanics in 1931, Dirac proposed the existence of the antielectron and the antiproton (see Moyer [2.1]). Just one year later, Anderson [2.2] reported the discovery of the antielectron, the so-called positron, e. Following thjs breakthrough, the muon pair x was found in 1937 (Neddermeyer and Anderson [2.3], Street and Stevenson [2.4], Nishina et al. [2.5]), and the charged and neutral pions (ir , ir°) were observed a decade later (Lattes et al. [2.6]). 

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