| Summary: | Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2017. === This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Cataloged from student-submitted PDF version of thesis. === Includes bibliographical references (pages 67-73). === A precision measurement of the cosmic antiproton ( -p) flux and the antiproton-to-proton flux ratio ( -p/p) made with the Alpha Magnetic Spectrometer aboard the International Space Station is presented. The measurement covers the absolute rigidity range from 1 to 450 GV, and is based on 3.49x105 -p events and 2.42x109 proton (p) events. This completes the measurements of the fluxes and flux ratios for the charged elementary particles in cosmic rays by AMS. In the absolute rigidity range 60 to 500 GV, the -p , p, and positron (e+) fluxes are found to have nearly identical rigidity dependence. This contrasts with the electron (e-) flux, which exhibits a different rigidity dependence. Below 60 GV, the ( -p/p), ( -p/e+), and (p/e+) flux ratios each reach a maximum. From 60 to 500 GV, the ( -p/p), ( -p/e+), and (p/e+) flux ratios show no rigidity dependence. These are new observations on the properties of charged elementary particles in cosmic rays. === by Andrew Ian Chen. === Ph. D.
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