Trapped Antihydrogen in Its Ground State

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Trapped Antihydrogen in Its Ground State

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Title: Trapped Antihydrogen in Its Ground State
Author: Richerme, Philip
Citation: Richerme, Philip. 2012. Trapped Antihydrogen in Its Ground State. Doctoral dissertation, Harvard University.
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Abstract: Antihydrogen atoms \((\bar{H})\) are confined in a magnetic quadrupole trap for 15 to 1000 s - long enough to ensure that they reach their ground state. This milestone brings us closer to the long-term goal of precise spectroscopic comparisons of \(\bar{H}\) and H for tests of CPT and Lorentz invariance. Realizing trapped \(\bar{H}\) requires characterization and control of the number, geometry, and temperature of the antiproton \((\bar{p})\) and positron \((e^+)\) plasmas from which \(\bar{H}\) is formed. An improved apparatus and implementation of plasma measurement and control techniques make available \(10^7 \bar{p}\) and \(4 \times 10^9 e^+\) for \(\bar{H}\) experiments - an increase of over an order of magnitude. For the first time, \(\bar{p}\) are observed to be centrifugally separated from the electrons that cool them, indicating a low-temperature, high-density \(\bar{p}\) plasma. Determination of the \(\bar{p}\) temperature is achieved through measurement of the \(\bar{p}\) evaporation rate as their confining well is reduced, with corrections given by a particle-in-cell plasma simulation. New applications of electron and adiabatic cooling allow for the lossless reduction in \(\bar{p}\) temperature from thousands of Kelvin to 3.5 K or colder, the lowest ever reported. The sum of the 20 trials performed in 2011 in which \(\bar{p}\) and \(e^+\) mix to form \(\bar{H}\) in the presence of a magnetic quadrupole trap reveals a total of \(105 \pm 21\) trapped \(\bar{H}\), or \(5 \pm 1\) per trial on average. This result paves the way towards the large numbers of simultaneously trapped \(\bar{H}\) that will be necessary for laser spectroscopy.
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