Measuring the free fall of antihydrogen

After the first production of cold antihydrogen by the ATHENA and ATRAP experiments ten years ago, new second-generation experiments are aimed at measuring the fundamental properties of this anti-atom. The goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is to test the weak equivalence principle by studying the gravitational interaction between matter and antimatter with a pulsed, cold antihydrogen beam. The experiment is currently being assembled at CERN's Antiproton Decelerator. In AEGIS, antihydrogen will be produced by charge exchange of cold antiprotons with positronium excited to a high Rydberg state (n > 20). An antihydrogen beam will be produced by controlled acceleration in an electric-field gradient (Stark acceleration). The deflection of the horizontal beam due to its free fall in the gravitational field of the earth will be measured with a moire deflectometer. Initially, the gravitational acceleration will be determined to a precision of 1%, requiring the detection of about 105 antihydrogen atoms. In this paper, after a general description, the present status of the experiment will be reviewed

Imaging a positronium cloud in a 1 Tesla

We report on recent developments in positronium work in the frame of antihydrogen production through charge exchange in the AEgIS collaboration [1]. In particular, we present a new technique based on spatially imaging a cloud of positronium by collecting the positrons emitted by photoionization. This background free diagnostic proves to be highly efficient and opens up new opportunities for spectroscopy on antimatter, control and laser manipulation of positronium clouds as well as Doppler velocimetry

Gravity and antimatter: The AEgIS experiment at CERN

From the experimental point of view, very little is known about the gravitational interaction between matter and antimatter. In particular, the Weak Equivalence Principle, which is of paramount importance for the General Relativity, has not yet been directly probed with antimatter. The main goal of the AEgIS experiment at CERN is to perform a direct measurement of the gravitational force on antimatter. The idea is to measure the vertical displacement of a beam of cold antihydrogen atoms, traveling in the gravitational field of the Earth, by the means of a moiré deflectometer. An overview of the physics goals of the experiment, of its apparatus and of the first results is presented

Towards the first measurement of matter-antimatter gravitational interaction

The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is a CERN based experiment with the central aim to measure directly the gravitational acceleration of antihydrogen. Antihydrogen atoms will be produced via charge exchange reactions which will consist of Rydberg-excited positronium atoms sent to cooled antiprotons within an electromagnetic trap. The resulting Rydberg antihydrogen atoms will then be horizontally accelerated by an electric field gradient (Stark effect), they will then pass through a moiré deflectometer. The vertical deflection caused by the Earth's gravitational field will test for the first time the Weak Equivalence Principle for antimatter. Detection will be undertaken via a position sensitive detector. Around 103 antihydrogen atoms are needed for the gravitational measurement to be completed. The present status, current achievements and results will be presented, with special attention toward the laser excitation of positronium (Ps) to the n=3 state and the production of Ps atoms in the transmission geometry

Towards the first measurement of matter-antimatter gravitational interaction

The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is a CERN based experiment with the central aim to measure directly the gravitational acceleration of antihydrogen. Antihydrogen atoms will be produced via charge exchange reactions which will consist of Rydberg-excited positronium atoms sent to cooled antiprotons within an electromagnetic trap. The resulting Rydberg antihydrogen atoms will then be horizontally accelerated by an electric field gradient (Stark effect), they will then pass through a moiré deflectometer. The vertical deflection caused by the Earth's gravitational field will test for the first time the Weak Equivalence Principle for antimatter. Detection will be undertaken via a position sensitive detector. Around 103 antihydrogen atoms are needed for the gravitational measurement to be completed. The present status, current achievements and results will be presented, with special attention toward the laser excitation of positronium (Ps) to the n=3 state and the production of Ps atoms in the transmission geometry

Compression of a mixed antiproton and electron non-neutral plasma to high densities

We describe a multi-step “rotating wall” compression of a mixed cold antiproton–electron non-neutral plasma in a 4.46 T Penning–Malmberg trap developed in the context of the AE¯gIS experiment at CERN. Such traps are routinely used for the preparation of cold antiprotons suitable for antihydrogen production. A tenfold antiproton radius compression has been achieved, with a minimum antiproton radius of only 0.17 mm. We describe the experimental conditions necessary to perform such a compression: minimizing the tails of the electron density distribution is paramount to ensure that the antiproton density distribution follows that of the electrons. Such electron density tails are remnants of rotating wall compression and in many cases can remain unnoticed. We observe that the compression dynamics for a pure electron plasma behaves the same way as that of a mixed antiproton and electron plasma. Thanks to this optimized compression method and the high single shot antiproton catching efficiency, we observe for the first time cold and dense non-neutral antiproton plasmas with particle densities n ≥ 1013 m−3 , which pave the way for an efficient pulsed antihydrogen production in AE¯gIS

Imaging a positronium cloud in a 1 Tesla

We report on recent developments in positronium work in the frame of antihydrogen production through charge exchange in the AEgIS collaboration [1]. In particular, we present a new technique based on spatially imaging a cloud of positronium by collecting the positrons emitted by photoionization. This background free diagnostic proves to be highly efficient and opens up new opportunities for spectroscopy on antimatter, control and laser manipulation of positronium clouds as well as Doppler velocimetry

Producing long-lived 2 3S positronium via 3 3P laser excitation in magnetic and electric fields

Producing positronium (Ps) in the metastable 2 3 S state is of interest for various applications in fundamental physics. We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3 3 P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm−1. The evidence of the 2 3 S state production is obtained to the 3.6σ level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra. The dynamic of the Ps population on the involved levels has been studied with a rate equation model

Antiproton tagging and vertex fitting in a Timepix3 detector

Studies of antimatter are important for understanding our universe at a fundamental level. There are still unsolved problems, such as the matter-antimatter asymmetry in the universe. The AEgIS experiment at CERN aims at measuring the gravitational fall of antihydrogen in order to determine the gravitational force on antimatter. The proposed method will make use of a position-sensitive detector to measure the annihilation point of antihydrogen. Such a detector must be able to tag the antiproton, measure its time of arrival and reconstruct its annihilation point with high precision in the vertical direction. This work explores a new method for tagging antiprotons and reconstructing their annihilation point. Antiprotons from the Antiproton Decelerator at CERN were used to obtain data on direct annihilations on the surface of a silicon pixel sensor with Timepix3 readout. These data were used to develop and verify a detector response model for annihilation of antiprotons in this detector. Using this model and the antiproton data it is shown that a tagging efficiency of 50± 10% and a vertical position resolution of 22 ± 0.5 μm can be obtained