Again the source is cosmic rays produced in the

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Again, the source is cosmic rays produced in the atmosphere. The muon behaves identally to an electron, except: It is about 200 times as massive It’s unstable, and decays in about 2x10 -6 [s] = 2 [ s] ( e + + ) More on these guys later Note that many muons are able to reach the earth from the upper atmosphere because of time dilation ! Because of their large speed, w observe that their “clocks” run slow they can live longer !!!
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Discovery of the Pion Cecil Powell and colleagues at Bristol University used alternate types of detection devices to see charged tracks (called “emulsions”) in the upper atmosphere. In 1947, they annouced the discovery of a particle called the -meson or pion ( ) for short. Pion ( ) comes to rest here, and then decays:      Two neutrinos are also produces but escape undetected. e Muon ( ) comes to rest here, and then decays: e     Two more neutrinos are also produced but also escape undetected. Cecil Powell 1903-1969 1950 Nobel Prize winner
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The Plethora of Particles Because one has no control over cosmic rays (energy, types of particles, location, etc), scientists focused their efforts on accelerating particles in the lab and smashing them together . Generically people refer to them as “ particle accelerators ”. (We’ll come back to the particle accelerators later…) Circa 1950, these particle accelerators began to uncover many new particles. Most of these particles are unstable and decay very quickly, and hence had not been seen in cosmic rays. Notice the discovery of the proton’s antiparticle , the antiproton , in 1955 ! Yes, more antimatter !
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  • Spring '18
  • Da-Ming Zhu
  • Electron, Positron, Positron Discovery

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