Abstract
We characterized the pulsed Rydberg-positronium production inside the AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) apparatus in view of antihydrogen formation by means of a charge exchange reaction between cold antiprotons and slow Rydberg-positronium atoms. Velocity measurements on positronium along two axes in a cryogenic environment (10K) and in 1T magnetic field were performed. The velocimetry was done by MCP-imaging of photoionized positronium previously excited to the $n=3$ state. One direction of velocity was measured via Doppler-scan of this $n=3$-line, another direction perpendicular to the former by delaying the exciting laser pulses in a time-of-flight measurement. Self-ionization in the magnetic field due to motional Stark effect was also quantified by using the same MCP-imaging technique for Rydberg positronium with an effective principal quantum number $n_{eff}$ ranging between 14 and 22. We conclude with a discussion about the optimization of our experimental parameters for creating Rydberg-positronium in preparation for an efficient pulsed production of antihydrogen.
Highlights
Antimatter has been thoroughly studied for almost a century first theoretically, when the antiparticle of the electron—the positron (e+)—emerged from Dirac’s equations [1], and a few years later experimentally, when Anderson observed it for the first time [2]
The self-ionization of positronium due to the motional Stark effect has been studied as a function of the wavelength of the IR laser exciting Ps-to-Rydberg states, with an effective principal quantum number neff ranging between 14 and 22
In the case of velocimetry, positronium was photoionized after excitation, 013101-7
Summary
Antimatter has been thoroughly studied for almost a century first theoretically, when the antiparticle of the electron—the positron (e+)—emerged from Dirac’s equations [1], and a few years later experimentally, when Anderson observed it for the first time [2]. The current goal of AEgIS is to demonstrate pulsed cold antihydrogen production via charge-exchange reaction [17], Ps∗ + p → e− + H ∗,. Where Ps∗ is a positronium atom excited to a Rydberg state, and a state with high principal quantum number n, the symbol pdenotes an antiproton, e− is the standard electron, and H ∗ is a Rydberg-antihydrogen atom. As the experiment has to be executed in a strong magnetic field of 1 T, the addressed Rydberg state must not be too high in order to avoid Ps self-ionization. The velocity of the produced Ps and the fraction of Rydberg-Ps surviving self-ionization caused by motional Stark effects in the magnetic field [19] have been characterized in view of the optimization of the charge-exchange cross section. We present the experimental results of the Ps-source characterization and the techniques by which we adjusted the system’s parameters for creating Rydberg-Ps in view of antihydrogen production
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