Mesonic atoms

Deser S., Goldberger M. L., Baumann K. and Thirring W. Energy Level Displacements in Pi-Mesonic Atoms, Phys. Rev. 96, 774-776 (1954) Anagnostopoulos D. F. et al., Precision measurements in pionic hydrogen, Nucl. Phys. A 721, 849-852 (2003). 

The formation and destruction of the mesonic atoms formed by the capture of if mesons can result in the emission of V/ 12—17 charged particles from a single lattice site. The estimation was made that a temp of 104° would be produced over a 10A radius for a period of 10"11 seconds. The calcs indicated that the high temp would quickly decrease but that the radius of the heat site would broaden and meet the criteria set forth by Bowden for a hot spot... 

An analysis of the hot-spot model was attempted by Cemy and Kaufman [50], who irradiated several explosives with tt" mesons (pions). The decay of mesonic atoms formed by the capture of n mesons can result in the emission of 12-17 charged particles from a single lattice site. It was estimated that a temperature of IO" °C would be produced over a 10-A radius for 10 " sec. The calculations indicated that the temperature would decrease rapidly, but that the radius of a hot-spot site would increase to meet the criterion of Bowden. 

The main relativistic effects come not from the terms arising from 1/r, being made Lorenz invariant, but from the one-electron terms (H and H4) in Eq. (2) of Reference 98 (see also Reference 96). The increase in the mass of an electron at higher velocities causes, as in mesonic atoms, (i) tighter binding to nuclei and ( ) contraction of the orbits. These effects that come from the one-electron terms are included in the relativistic Hartree-Fock method. > ... 

Mesonic atoms can be regarded as new types of nuclear probes in material science dealing with chemical aspects. In this section, capture ratio problems in binary systems as well as X-ray intensity patterns in mesonic transitions are briefly described. 

In more detailed papers, Wheeler stressed the possibility of obtaining the size of the charge distribution of the nucleus from measurements of the energy of these X-rays from [jl mesonic atoms. 

Muoniiim, a pseudo-atom involving a negative muon moving about a proton, has also been observed. Other mesonic atoms, having structures similar to ordinary atoms but with a muon or other meson replacing one of the electrons, have also been observed. For example, muonic neon is a neon atom with a negative muon in place of an electron. 

Our present views on the electronic structure of atoms are based on a variety of experimental results and theoretical models which are fully discussed in many elementary texts. In summary, an atom comprises a central, massive, positively charged nucleus surrounded by a more tenuous envelope of negative electrons. The nucleus is composed of neutrons ( n) and protons ([p, i.e. H ) of approximately equal mass tightly bound by the force field of mesons. The number of protons (2) is called the atomic number and this, together with the number of neutrons (A ), gives the atomic mass number of the nuclide (A = N + Z). An element consists of atoms all of which have the same number of protons (2) and this number determines the position of the element in the periodic table (H. G. J. Moseley, 191.3). Isotopes of an element all have the same value of 2 but differ in the number of neutrons in their nuclei. The charge on the electron (e ) is equal in size but opposite in sign to that of the proton and the ratio of their masses is 1/1836.1527. 

After the discovery of the combined charge and space symmetry violation, or CP violation, in the decay of neutral mesons [2], the search for the EDMs of elementary particles has become one of the fundamental problems in physics. A permanent EDM is induced by the super-weak interactions that violate both space inversion symmetry and time reversal invariance [11], Considerable experimental efforts have been invested in probing for atomic EDMs (da) induced by EDMs of the proton, neutron, and electron, and by the P,T-odd interactions between them. The best available limit for the electron EDM, de, was obtained from atomic T1 experiments [12], which established an upper limit of de < 1.6 x 10 27e-cm. The benchmark upper limit on a nuclear EDM is obtained from the atomic EDM experiment on Iyt,Hg [13] as d ig < 2.1 x 10 2 e-cm, from which the best restriction on the proton EDM, dp < 5.4 x 10 24e-cm, was also obtained by Dmitriev and Senkov [14]. The previous upper limit on the proton EDM was estimated from the molecular T1F experiments by Hinds and co-workers [15]. 

In 1934 the Japanese physicist Hideki Yukawa postulated the existence of yet another force particle, which he called the meson. In 1932 Yukawa began his academic career with an appointment at Osaka Imperial University, which had been founded the previous year. The discovery of the neutron and the publication of Fermi s theory started him thinking about the nature of the force that bound protons and neutrons together in an atomic nucleus. He realized that, though... 

By then the quest had passed from the hands of the chemists into those of the physicists, who made a series of discoveries that were eerily like those that had been made in chemistry. Physicists discovered new particles until the number of known particles grew beyond reason. Then, like their predecessor Mendeleev, Gell-Mann and Ne eman discovered a hidden order. Like Bohr, who had probed the workings of the atom, Gell-Mann and Zweig theorized about the inner mechanisms of mesons and baryons, introducing the concept of the quark. 

The Total Bary on Number Remains Constant. A baryon is a nucleon (proton or neutron) or any panicle heavier than those that can he considered to have an atomic mass number A — I. Some mesons have a mass greater than the proton, but they have a mass number. 4 - 0. so they are not barvuns. In computing the number or barvons present in a system, each baryon counts I each ami baryon counts — I and leptons and mesons count 0. 

A considerable amount of evidence indicates that nuclear forces are charge-independent, i.e, the neutron-neutron, neutron-proton, and proton-proton forces are identical. The meson theory of nuclear forces, originated by Yukawa, postulates the atomic nucleus being held together by an exchange force in which particles, now called mesons, are exchanged between individual nucleons within the nucleus. 

The mechanism of Aab creation is the Coulomb interaction in the final state (between a+ and b ), formatting from two virtual particles a+ and b, the bound state Aab (Fig. 1). This mechanism, in principle, allows for creation of all types of bound states and if a+ and b are relativistic particles, then Aab will also be relativistic. For ultra-relativistic atoms, there are effects caused by final time of atom formation and new phenomena during atom interaction with matter. High value of the Lorentz factors of atoms also allows for the detection new short lived bound states An, Ao and A k, consisting accordingly from (7r+p ), (7r+7r ) and (tt+ K ) mesons and to measure their parameters. 

Section 4 describes the atoms consisting of 7r+ and 7r mesons (A2v) and experiments involving their detection and lifetime measurement. The lifetime of A2jt is determined by the charge-exchange process... 

Investigation of atoms consisting of tt and p mesons (Avll), in principle, allows one to obtain the pion charge radius in a model independent way. 

The basic properties of Avtl are calculable with the formalism used to describe the hydrogen atom. The reduced mass of the system is 60.2MeV/c, its Bohr radius is 4.5 10-11cm, and the binding energy of the 1Si/2 state is 1.6 keV. These atoms are produced in the decay (1) of AT mesons (Fig. 2). 

A different method became available with modern meson factories, where the characteristic X-radiation from exotic atoms can be studied under optimized conditions and with reasonable count rates. Such experiments require the use of high-intensity external beam lines together with a particle concentrator like the cyclotron trap and a high-resolution low-energy crystal spectrometer. 

Administratum has an atomic mass of 311, since the neutron is only detectable half of the time. Its 312 particles are held together by a force which involves the continuous exchange of meson-like particles, called morons. 

Several decades ago the number of elementary particles known was limited, and the system of elementary particles seemed to be comprehensible. Electrons had been known since 1858 as cathode rays, although the name electron was not used until 1881. Protons had been known since 1886 in the form of channel rays and since 1914 as constituents of hydrogen atoms. The discovery of the neutron in 1932 by Chadwick initiated intensive development in the field of nuclear science. In the same year positrons were discovered, which have the same mass as electrons, but positive charge. All these particles are stable with the exception of the neutron, which decays in the free state with a half-life of 10.25 min into a proton and an electron. In the following years a series of very unstable particles were discovered the mesons, the muons, and the hyperons. Research in this field was stimulated by theoretical considerations, mainly by the theory of nuclear forces put forward by Yukawa in 1935. The half-lives of mesons and muons are in the range up to 10 s, the half-lives of hyperons in the order of up to 10 s. They are observed in reactions of high-energy particles. 

The cosmic radiation incident on the earth is generated in our galaxy. It is effectively absorbed in the atmosphere, and the flux density is reduced from about 20 cm s to about 1 cm" s at the surface of the earth. By interaction with the atoms and the molecules in the atmosphere showers of elementary particles are produced, making up the secondary cosmic radiation. Positrons, muons, several kinds of mesons and baryons were first detected in the secondary cosmic radiation. Furthermore, nuclear reactions induced by secondary cosmic radiation lead to the production of cosmogenic radionuchdes, such as T and (section 1.2). 

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