Abstract
We report experiments in which radiatively metastable 2,^{3}mathrm {S}_{1} positronium (Ps) atoms entered a waveguide whose internal surfaces were lined with smoked magnesium oxide (MgO) powder. The waveguide was built such that time-delayed microwave radiation pulses, tuned to drive 2,^{3}mathrm {S}_{1}rightarrow 2,^{3}mathrm {P}_{2} transitions, could be applied to the Ps ensemble. The lifetime of 2,^{3}mathrm {S}_{1} atoms was measured using time-delayed microwave induced decay, yielding ≈200 ns. This is considerably shorter than the Zeeman shifted lifetime of 1070 ns, indicating that Ps atoms in the 2,^{3}mathrm {S}_{1} state do not survive multiple collisions with MgO nanocrystals.
Highlights
Positronium (Ps) [1] is a hydrogenic atomic system composed of an electron bound to a positron via the Coulomb interaction
We report the results of experiments in which atoms excited to the 2 3S1 state were allowed to fly into a WR-112 waveguide whose internal surfaces were lined with magnesium oxide (MgO) nanocrystals
For each spectrum the amplitudes of the smoothed peaks were evaluated at 100 ns intervals corresponding to the times at which the microwave radiation pulses were applied, taking into account a 70 ns delay between the application of the microwave pulse and the peak amplitude of the subsequent annihilation pulse. This delay is due to the ground state decay rate and the Lutetium Yttrium Oxyorthosilicate (LYSO) detector response
Summary
Positronium (Ps) [1] is a hydrogenic atomic system composed of an electron bound to a positron via the Coulomb interaction. The fact that Ps is composed of low mass leptons means that it is, for any experimentally relevant regimes, fully described by quantum electrodynamics (QED). The absence of any hadronic contribution to its structure means that Ps is the ideal system to test bound-state QED theory [3]. There have been many experimental tests of QED using Ps [5, 6], based primarily on precision measurements of annihilation decay rates [7,8,9,10] and energy levels [11,12,13,14,15,16,17,18,19,20,21,22,23]. Most of the previous precision Ps measurements were performed decades ago, and subsequent technological advances have made it feasible to make significant improvements to these measurements, for example, new positron trapping techniques [25] and laser metrology [26]
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