My notes from the lecture (if they don’t make sense then it is entirely my fault) He was awarded the 2012 IUPAPC11 young scientist prize and the 2013 American Physical Society Henry Primoakoff award on his work on neutrino physics. He has a wide interest in physics, from nuclear physics and particle physics to theoretical and experimental astrophysics. He obtained his PhD from Indiana University, Bloomington, USA and after doing a postdoc at MIT he came to the UK for his current position. For photon energies far above this threshold, pair production becomes the dominant mode for the interaction of x-rays and gamma-rays with matter.BibhutibhusanPatel on Particle physics – Beyond the…ĭr Katori is a senior lecturer at Queen Mary University of London. The rest mass energy of the electron is 0.511 MeV, so for photon energy above 1.022MeV, pair production is possible. When a photon has quantum energy higher than the rest mass energy of an electron plus a positron, one of the ways that such a photon interacts with matter is by producing and electron-positron pair. Another interesting application is the use of the coincident gammas to locate the source by back projecting. For one thing, eliminating all gamma events which are not coincident at 180 degrees improves the signal-to-noise ratio of experiments using positron annihilation. These coincident gamma rays at 180 degrees provide a useful analysis tool. The energy released by the annihilation forms two highly energetic gamma rays, and if one assumes that the momenta of the positron and electron were equal before the annihilation, the two gamma ray photons must travel in opposite directions in order to conserve momentum. The positron is the antiparticle of the electron, and when a positron enters any normal matter, it will find an abundant supply of electrons with which to annihilate. The tau is the only lepton massive enough to decay into hadrons, particularly into pions. The discovery contributed to the Nobel Prize awarded to Martin Lewis Perl in 1995. The tau lepton was detected in experiments at SLAC and LBL between 19. The tau lepton has spin 1/2 like the electron and muon leptons and an antiparticle with equal mass but opposite charge. Its mass is some 17 times that of the muon, the other massive lepton. The tau is the most massive of the leptons, having a rest mass some 3490 times the mass of the electron, also a lepton. (Richtmyer) The average sea level muon flux is about 1 muon per square centimeter per minute. Muons make up more than half of the cosmic radiation at sea level, the remainder being mostly electrons, positrons and photons from cascade events. Measuring the flux of muons of cosmic ray origin at different heights above the earth is an important time dilation experiment in relativity. The muon is produced in the upper atmosphere by the decay of pions produced by cosmic rays: The lifetime of the muon is 2.20 microseconds. The fact that the above decay is a three-particle decay is an example of the conservation of lepton number there must be one electron neutrino and one muon neutrino or antineutrino in the decay. The muon is a lepton which decays to form an electron or positron. What evidence suggests that the electron is a fundamental particle? Associated with the electron is the electron neutrino. On the other hand, one of the mechanisms for the interaction of radiation with matter is the pair production of an electron-positron pair. If an electron and a positron encounter each other, they will annihilate with the production of two gamma-rays. The electron's antiparticle, the positron, is identical in mass but has a positive charge. It is a fermion of spin 1/2 and therefore constrained by the Pauli exclusion principle, a fact that has key implications for the building up of the periodic table of elements. Table of lepton propertiesĪs one of the leptons, the electron is viewed as one of the fundamental particles. The observed abundance agrees with three types of neutrinos. When the process of nucleosynthesis from the big bang is modeled, the number of types of neutrinos affects the abundance of helium. One of the pieces of experimental evidence for that is the measured hydrogen/helium abundance ratio in the universe. The present standard model assumes that there are no more than three generations. Now that we have experimental evidence for six leptons, a relevant question is "Are there more?". Important principles for all particle interactions are the conservation of lepton number and the conservation of baryon number. The different varieties of the elementary particles are commonly called "flavors", and the neutrinos here are considered to have distinctly different flavor. There are six leptons in the present structure, the electron, muon, and tau particles and their associated neutrinos. ![]() Leptons and quarks are the basic building blocks of matter, i.e., they are seen as the "elementary particles".
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