Muons decay process

Let us first assume that the external field is switched off. Furthermore, we have assumed that internal fields do not exist (nonmagnetic sample). Thus, no magnetic interaction works on Sy, which remains stationary. Under those circumstances Nf(t) simply reflects the muon decay process ... 

We do not find it productive to involve our analysis into further speculations that will include the decay processes of muons and pions, and their mean lives in order to find out which version is more acceptable, that with muons or with pions. It is well known that the muon s mean life changes as a function of its velocity however, there are no data regarding what happens with decay processes with particles that reach velocities v > c [11]. 

This decay process is mediated by the weak interaction , thus involves no conservation of parity, and as a consequence the emitted positron emerges predominantly along the direction of the muon spin at the moment of decay [8]. The decay positrons are easily detected, as sparks of light in scintillators placed around the sample, and give the direction of the muon spin at the moment of decay. This therefore provides a way of monitoring the evolution of the muon spin well within the sample, and is the basis of jxSR. 

Another method of orientating an emitter in its initial state and then observing the angular correlation of the subsequent radiation is used in /tSR spectroscopy. First a pion decays into a muon and a mesonic neutrino. This process determines the spin polarisation of the muon at the time of its creation. Subsequently after a mean lifetime of approximately 2.2 x 10 s the muon decays into a positron, a leptonic neutrino and a mesonic antineutrino. 

Neutrinos may be absorbed in nuclei with the emission of an electron, a muon, or a tauon, depending on the incident neutrino type. These are called inverse-beta-decay processes because they are, in the case of the electron neutrino, the inverse of normal radioactive beta-decay. Neu-... 

There are six different kinds of leptons (light particles) (Table 1.6), and they can be arranged in three pairs. The electron (e), the muon (p,), and the tau lepton (t) each carry a charge of —e and have associated with them the electron (ve), muon (VjJ, and tau neutrinos (vT). These neutrinos are electrically neutral and have small or zero rest mass. The actual mass of the neutrinos is a subject of current research (see Chapter 12). The electron neutrino is seen in nuclear phenomena such as (3 decay, whereas the other neutrinos are involved in higher energy processes. 

A single muon stopped in a target of deuterium-tritium mixture can catalyze more than 100 fusions, but this number is limited by two major bottle-necks. One is the rate at which a muon can go through the catalysis cycle before its decay (cycling rate), and another is a poisoning process called p-a sticking in which, with a probability u)s < 0.01, the muon gets captured after the fusion reaction to atomic bound states of the fusion product 4He, and hence lost from the cycle (see Section 5). 

The conversion of muonium (y+e ) to its antiatom antimuonium (y e+) would be an example of a muon number violating process,2 and like neutrinoless double beta decay would involve ALe=2. The M-M system also bears some relation to the K°-K7r system, since the neutral atoms M and M are degenerate in the absence of an interaction which couples them. In Table III a four-Fermion Hamiltonian term coupling M and M is postulated, and the probability that M formed at time t=0 will decay from the M mode is given. Present experimental limits22 23 for the coupling constant G are indicated and are larger than the Fermi constant Gp. 

Few of the pions formed in the annihilation process reach the earth s surface. They undergo radioactive decay (life-time about 10 s) to muons and neutrinos, or they collide with other particles in the atmosphere and are annihilated. The muons have properties similar to the electron, but are unstable, decaying with a life-time of about 2 x lO s to electrons and neutrinos. The collision reactions of the pions result in the formation of a large number of other particles such as electrons, neutrons, protons, and photons. Some of the electrons so formed are captured in a thick zone around the earth known as the inner van Allen belt. 

In this zoo of particles, only the electron, which was discovered even before the atomic theory was proven and the atomic structure was known, is really unseeable, stable, and isolatable. The proton also is stable and isolatable, but it is made up of two quarks up (with charge -1-2/3) and one quark down (with charge —1/3). As for the quarks, while expected to be stable, they have not been isolated. The other particle constitutive of the atomic nucleus, the neutron, is also made up of three quarks, one up and two down, but it is not stable when isolated, decaying into a proton, an electron, and an antineutrino (with a 15-min lifetime). The fermions in each of the higher two classes of the electron family (muon and tau) and of the two quark families (strange charmed and bottom/top) are unstable (and not isolatable for the quarks). Only the elusive neutrinos in the three classes, which were postulated to ensure conservation laws in weak interaction processes, are also considered as being unseeable, stable, and isolatable. 

As noted earlier, the classic/a SR experiment is carried out in a transverse magnetic field, in which case the ft-e decay pattern processes in the field at the muon Larmor frequency. 

The CP non-invariance is demonstrated also in the semileptonic (1) decay modes of Ki, mesons, in the Ki —> e+Ve7t , andi L —> e Ve7i processes, as well as similar ones in which muons are involved instead of electrons. The observed asymmetry (Al) of time-integrated semileptonic decay rates is... 

All of the members of the natural decay chains are unstable with respect to spontaneous fission, but the probabilities are small. The decay chains follow the side of the valley of stability where the fissionability parameter Z A is relatively small. However, fission is such an extraordinary event that even a few events can be detected, as long as they can be distinguished from events such as muon-induced fission. For the natural chains has the highest fraction of decays by spontaneous fission, 5.4 x 10. Although this leads to a multitude of natural decay chains consisting of fission followed by decays through fission product chains, the process will not be considered in this chapter. 

There are several cascade codes developed for reproducing the cascade decays of exotic atoms (see, e.g., Borie and Leon 1980 Markushin 1999 Jensen and Markushin 2002). The cascade process is studied by detecting X-rays and Auger electrons from transitions in all exotic atoms and via laser spectroscopy in metastable antiprotonic helium (see O Sect. 28.6.3.2). It was experimentally observed that medium-heavy muonic atoms such as p Ar lose all atomic electrons via Auger effect by the time the muon reaches the ground state (Bacher et al. 1988). 

Finally, availability of more exact data on the. -nucleus and p.-atom interactions is important in astrophysics, studying substance transformation in the Universe, testing the Standard Model etc. [6, 21,49, 50]]. e-p-Y-nuclear spectroscopy of atoms (molecules) opens new prospects in combining nuclear physics and quantum chemistry (atomic physics). These possibilities are strengthened by quickly developed nuclear quantum optics [19-26]. Superintense lasers (raser or even graser) field may provide a definite measurement of the change in the dynamics of the nuclear processes, including the muon capture (and/or y, P-, a-decay) [18-26,48,50],... 

Nuclear collisions. When elementary particles collide with each other or with a photon, other particles can be created that are often unstable, i.e., they decay into other particles and continue to do so until they reach a state where only stable particles result. Such a process is called a cascade. Common intermediate and final particles are the pion, the muon, the photon, and the neutrino. The pion comes in various forms, charged and uncharged, the muon is always charged, and the neutrino is always neutral. The neutrino is characterized by a very small interaction cross section with matter. Thepions have a mass, again in energy equivalents, of about 140 MeV, the muons of about 106 MeV, and the neutrinos of about 0.03 eV, a still rather uncertain number. 

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