AEgIS experiment

AEgIS will attempt to determine if gravity affects antimatter in the same way it affects normal matter by testing its effect on an antihydrogen beam. The aspired experimental setup uses the Moiré deflectometer to measure the vertical displacement of a beam of cold antihydrogen atoms traveling in Earth's gravitational field.^[4]

In the first phase of the experiment (running until 2018), antiprotons from the Antiproton Decelerator (AD) with a kinetic energy of 5.3MeV had to pass through a series of aluminum foils which acted as so-called degraders, slowing down a fraction of the fast antiprotons to few keV. The slow antiprotons were then further cooled by merging them with extra cold trapped electrons (electron cooling) and finally trapped inside a Malmberg–Penning trap.^[5] An intense radioactive β⁺ source (²²Na) was used to produce positrons, which were accumulated in a Surko-type storage trap at low pressure (3e-8 mbar). These positrons were implanted into a nano-structured porous silicon target in order to efficiently form positronium (Ps) - even at cryogenic temperatures in Ultra-high vacuum (UHV).^[6] A cloud of positronium emerging from the target was then excited to a Rydberg level of n=16/17 by using laser-induced two-step optical transitions.^[3] Inside the Malmberg–Penning trap, the charge exchange reaction between cold antiprotons and Rydberg-Ps took place, leading to the formation of Rydberg-antihydrogen with high efficiency in the form of a 4π pulse.^[7][8]

${\displaystyle \mathrm {Ps^{*}+{\bar {p}}\longrightarrow {\bar {H^{*}}}+e^{-}} }$ (Charge exchange reaction)

The following paragraph is out of date. It appears to have been written in 2014, nine years ago. In the 27 October 2023 issue of Nature, the ALPHA experiment published the result that antihydrogen falls.^[9]

In the second phase of the AEGIS experiment, starting from 2021 after AEgIS has been successfully connected to the new antiproton deceleration and storage ring ELENA, the Rydberg antihydrogen atoms will be channeled into a beam, which then will pass through a series of matter gratings, the central piece of a Moiré-deflectometer. The antihydrogen atoms will ultimately hit onto the surface of a position and time-resolving detector, where they will annihilate. Areas behind the gratings are shadowed, while those behind the slits are not. The annihilation locations reproduce a periodic pattern of light and shadowed areas. This pattern is highly sensitive to small vertical displacements of the anti-atoms during their horizontal flight - the Earth's gravitational force on antihydrogen can thus be determined.^[4]

The AEgIS collaboration comprises the following institutions:

1. Antiproton Decelerator
2. GBAR experiment
3. ALPHA experiment