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Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure

Gurung, Lokesh; (2021) Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

A new precision measurement of the positronium (Ps) 2³S₁ - 2³PJ (J=0, 1, 2) fine structure intervals is presented in this thesis. A Surko-type positron trap coupled to a radioactive ²²Na source was used to generate intense pulses of positrons to produce slow Ps atoms from a SiO₂ target. These atoms, initially in the ground state, were then optically excited with a UV laser in a region of applied electric field to generate atoms in the 2³S₁ state. The radiatively metastable atoms then travelled through a microwave guide where νJ = 2³S₁ - 2³PJ (J=0, 1, 2) transitions were driven with microwave radiation. Atoms in the 2³PJ states radiatively decay to the 1³S₁ state and the νJ transitions were observed via the time-dependent annihilation radiation of the ground state Ps. The ν₀ transition resonance frequency is measured to be ν₀ = 18501.02 ± 0.62 MHz. This is in disagreement with the theoretical calculation of ν₀ = 18498.25 ± 0.08 MHz by 2.77 MHz (4.5σ). The ν₁ and ν₂ transition lineshapes are observed to be asymmetric, which prevents the determination of the true resonance frequency. Known quantum interference effects are too small to account for the observed shift and the source of the asymmetry is not presently known. Our measurements, nevertheless, show an improvement in precision compared to previous experiments by a factor of ≈ 3-7. These new measurements mark progress in precision Ps physics, and future work to improve precision further and address the current discrepancies are outlined.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2021. 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 > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10125029
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