Observation of asymmetric line shapes in precision microwave spectroscopy of the positronium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>2</mml:mn><mml:mmultiscripts><mml:mi>S</mml:mi><mml:mn>1</mml:mn><mml:none/><mml:mprescripts/><mml:none/><mml:mn>3</mml:mn></mml:mmultiscripts><mml:mo>→</mml:mo><mml:mn>2</mml:mn><mml:mmultiscripts><mml:mi>P</mml:mi><mml:mi>J</mml:mi><mml:none/><mml:mprescripts/><mml:none/><mml:mn>3</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>J</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mo>,</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:math>) fine-structure intervals
L. Gurung, T. J. Babij, Jesús Pérez‐Ríos, S. D. Hogan, D. B. Cassidy
Abstract
We report new measurements of the positronium (Ps) $2^{3}S_{1}\ensuremath{\rightarrow}2^{3}P_{J}$ fine-structure intervals, ${\ensuremath{\nu}}_{J}$ ($J=0,1,2$). In the experiments, Ps atoms, optically excited to the radiatively metastable $2^{3}S_{1}$ level, flew through microwave radiation fields tuned to drive transitions to the short-lived $2^{3}P_{J}$ levels, which were detected via the time spectrum of subsequent ground-state Ps annihilation radiation. Both the ${\ensuremath{\nu}}_{1}$ and ${\ensuremath{\nu}}_{2}$ line shapes were found to be asymmetric, which, in the absence of a complete line-shape model, prevents accurate determination of these fine-structure intervals. Conversely, the ${\ensuremath{\nu}}_{0}$ line shape did not exhibit any significant asymmetry; the observed interval, however, was found to disagree with QED theory by 4.2 standard deviations.