Sheldon, Ross Edward;
(2024)
Tests of quantum electrodynamics using n = 2 positronium.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This work presents measurements of n = 2 Positronium (Ps) to explore and test bound state quantum electrodynamics theory. A pulsed positron beam was used to produce ground state Ps from a mesoporous silica target. The metastable 23S1 state was produced using a single-colour, single-photon laser excitation in an electric field to generate a Stark mixed state which evolved into the pure 23S1 state upon adiabatic removal of the electric field. In the first experiment the 23S1 annihilation decay rate was measured by determining the 23S1 population over time and correcting for losses. The final result was Γ2S =843±72 kHz, a precision of only 8.5%, but in agreement with theory at 890.0±1.4 kHz. This precision it is not sufficient to test QED corrections, but does represent the first measurement of a Ps excited state annihilation decay rate. In the second experiment ∼ 8.6 GHz microwave radiation from a horn antenna was used to investigate the effect of microwave reflection induced frequency dependent power on the measured resonance frequency and asymmetry of line shapes of the 23S1 →23P2 fine structure interval. This established that horn antennas create microwave fields with a significant component of reflected radiation, inducing shifts of ±4 MHz from the expected transition frequency but without asymmetry. Finally, in the third experiment, a new precision measurement of the 23S1 → 23P2 interval was made for a result of 8627.94 ± 0.95 MHz, 1.3σ from the theoretical value, an improvement over the previous measurement which was 4σ from theory and suffered from the reflection effects investigated in this work. However, microwave field effects within the waveguide are still the dominant source of error, therefore new interferometry techniques are proposed to overcome this.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Tests of quantum electrodynamics using n = 2 positronium |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10190892 |
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