cosmic_rays

cosmic_rays - Experiments in Modern Physics: Cosmic Rays...

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Experiments in Modern Physics: Cosmic Rays Rex Tayloe, Department of Physics, Indiana University 1/10/04 (revised from original by HOM, 12/98) Last Revised: 1/15/04 Goals Understand the 2 workings of high energy physics detectors and electronics. Use these to measure the rate of cosmic rays and the lifetime of the muon. Introduction Fast atomic particles are moving through interstellar space. The earth is thus under a constant bombardment by protons, and, to a lesser degree, by light nuclei (see ref. [1], fig.20.1). The average energy of these particles of in the order of 1 GeV, but can range to energies higher than those that can be produced by accelerators. When the particles make contact with the upper atmosphere, they start to undergo nuclear reactions with the air. Almost none of them reach the surface of the earth. However, the products of these reactions can survive. In high-energy collisions in the atmosphere, pions are produced in abundance. Pions have a mean life of only 26 ns (at the speed of light, they travel only about 8m). When they decay, they produce a muon ( ) and a neutrino ( ). The charged muons lose energy in the atmosphere, but an initial energy of about 1 GeV is enough to reach the surface of the earth. The muon is also unstable, decaying into an electron and two neutrinos with a mean life of about 2 s. Thus, it seems that the muons should decay before they reach the surface. However, according to special relativity, seen from an earth-bound observer, the muon clock runs slow by
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cosmic_rays - Experiments in Modern Physics: Cosmic Rays...

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