Muons positron

The muon spin relaxation technique uses the implantation and subsequent decay of muons, n+, in matter. The muon has a polarized spin of 1/2 [22]. When implanted, the muons interact with the local magnetic field and decay (lifetime = 2.2 ps) by emitting a positron preferentially in the direction of polarization. Adequately positioned detectors are then used to determine the asymmetry of this decay as a function of time, A t). This function is thus dependant on the distribution of internal magnetic fields within a... 

Fig. 1. Schematic for /zSR and fiLCR experiments. For pSR the muon spin polarization vector starts off in the x direction (open arrow). It then precesses about an effective field (the vector sum of the external field and the internal hyperfine field), which is normally approximately the z direction. The muons are detected in the M counter, and positrons from muon decay are detected in the L or R counters. For pLCR, the muon spin polarization is initially along the external field or t axis (solid arrow). The positron rates in the F and B counters are measured as a function of external field. A sharp decrease in the asymmetry of the F and B counting rates signifies a level crossing.

The actual eigenstates are equal admixtures of the two unperturbed pure spin states when the field is exactly at the value at which the crossing would have occurred (v,m = 0). Since initially (when the muon stops) the system is in a well defined muon spin state, i.e., one of the two unperturbed pure spin states, the system oscillates at the frequency vT between the muon spin being along and opposite to the field, as implied by Eqs. 10 and 11. Thus, upon time averaging the positron counts the forward-backward asymmetry is reduced. 

The HSCC equations have been solved for various Coulomb three-body processes, such as photoionization and photodetachment of two-electron systems and positronium negative ions [51, 105-111], electron or positron collisions [52, 112-115], ion-atom collisions [116-119], and muon-involving collision systems [103, 114, 120-125]. Figures 4.6, 4.7, 4.8, 4.9, and 4.10 are all due to HSCC calculations. Figure 4.12 illustrates the good agreement between the results of HSCC calculations [51] and the high-resolution photoionization experiment on helium [126]. See Ref. [127] for further detailed account of the comparison between the theory and experiment on QBSs of helium up to the threshold of He+(n = 9). 

Figure 16.24. Sensitivity of upcoming gamma-ray telescopes to neutralino models that can explain the HEAT positron excess with neutralino clumps in the galactic halo. Model points are indicated by crosses circles denote those models that in addition can also account for the measured deviation in the muon magnetic moment. The upper set of sensitivity curves corresponds to the high latitude gamma-ray line flux (scale on the left) the lower set of curves to the direction toward the galactic center (scale on the right no steep spike around the central black hole is assumed). (Figure from Baltz, Edsjo, Freese, Gondolo(2002).)...

One is based on a study of the possibility of the conversion of muonium f/i+e -system) to antimuonium (p e+-svstem) [12]. This is possible in the case of non-conservation of electronic charge (i.e. the number of electrons and electronic neutrinos minus the number of positrons and antineutrinos) and muonic charge (i.e. the number of muons and muonic neutrinos minus the number of their antiparticles). Both must be conserved separately with the Standard Model. 

Charged particles were detected by the telescopes Ti and T2. The track coordinates were measured by drift chambers. The time interval between detector hits in Ti and T2 was measured by scintillation hodoscopes. Electrons and positrons were rejected by gas Cherenkov counters, and muons by scintillation... 

Positronium (Ps, e+e ) is the bound state of an electron and its antiparticle the positron. Both constituents are structureless and pointlike leptons. The absence of structure avoids the difficulties encountered in hydrogen due to the composite nature of the proton. The advantage, compared with muonium (p+e-) is the absence of an additional free parameter like the muon mass. Ps is completely described by only two fundamental constants [1,2], the Rydberg constant... 

In the case of an exotic atom, physicists bring together an exotic particle and an ordinary particle or two exotic particles to form a short-hved entity that is structurally like hydrogen. The exotic particles involved are unstable and have short lifetimes. For example, one such exotic particle, the muon, has a mean fifetime of 2.1971 X 10 seconds the positron is stable when isolated, but it... 

In positronium a positron is substituted for the proton and the positron and an electron are bound together in a hydrogen-like atom. Muonic hydrogen, perhaps the simplest exotic atom, unites a negatively charged muon with a positively charged proton. In this instance, a muon simply replaces the electron. In muonium, an electron is bound to a positive muon. As we shall see, there are other examples of exotic atoms. Positronium, muonic hydrogen, and muonium have been studied rather extensively. 

The technique of muon spin rotation involves applying a magnetic field perpendicular to the direction of the incoming beam of muons (transverse to their spin) and monitoring the resulting precession signal via the emission of positrons that are emitted preferentially in the direction of the muon spin at the moment of its radioactive decay. For the bare muons this is simply the Larmor frequency but for muonium several frequencies are observed. In the case of a small h q)erfine constant, one can easily reach the so-called Paschen-Back regime in moderate fields and then a triplet of lines is seen in a Fourier transform of the raw data. 

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. 

A positron, having given off its energy by interaction with matter, may coexist with an electron for a short time in the form of a positronium atom (c e ) before annihilation occurs. Absorption of other short-lived elementary particles such as muonS pions, kaons or sigma particles may lead to substitution of protons or electrons, respectively, in atoms or molecules, with the result of formation of so-called exotic atoms or molecules. Although the lifetime of these species is very short... 

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). 

---