AEGIS - Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy

The primary scientific goal of the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) is the direct measurement of the Earth's gravitational acceleration, g, using antihydrogen at the European laboratory for particle physics (CERN), as a test of the Weak Equivalence Principle In the first phase of the experiment, we will use antiprotons from the Antiproton Decelerator, together with a pulse of laser-excited positronium atoms (obtained by shooting positrons onto a nano-structured target) to make a pulse of horizontally-travelling antihydrogen atoms.

The Science

The scientific goal of the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) is the direct measurement of the Earth's gravitational acceleration g on antihydrogen. Details of the experiment and a photo-gallery can be found in
The AEGIS experiment is a collaboration of physicists coming from twenty European Institutes and Universities. An Antihydrogen beam will be formed by charge exchange between antiprotons and laser-excited positronium atoms obtained by injecting bunched positrons in an ordered nano-structured target. The strength of the gravitational force between the Earth and the antihydrogen atoms will be measured sending an antihydrogen beam through a moiré deflectometer and observing the periodic pattern recorded by a detector which combines silicon strips and photographic emulsion plates.
The role of the Trento positron group in AEGIS is mainly related to the positron manipulation (production of positron bunches with a Surko-apparatus), production of cooled positronium with ordered nano-structured targets, off-line positronium spectroscopy in a dedicated apparatus. (See sketch of the AEGIS experiment, below)

Positronium TIME of Flight at NEPOMUC (FRMII)
Recently the Trento positron group used nanochannelled silicon targets to form high yield of positronium (PRB 235418, 2010) and to cool down, by collisional cooling, positronium at temperature as low as 150 K (PRL 243401, 2010). These first results were obtained by avoiding the positronium quantum confining in porous media (PRB 085428, 2008). To study in details positronium formation and cooling at lower temperatures a Ps-TOF (Positronium time of flight) apparatus was designed and assembled at the free positron beam port of the high intensity positron source NEPOMUC ( NEutron POsitron MUniCh) at the FRMII reactor at Garching – München At present the apparatus is under data taking. (See sketch of the FRMII, below)

Slow Positron Beam in Trento laboratory
The positron Trento laboratory is equipped with a slow continuous positron beam that allows studies of vacancy-like defects, open volumes and free volumes in solids by the Doppler Broadening technique and the 2γ-3γ annihilation ratio of positronium (3γ-PAS) measurements. Different ordered and disordered porous material and membranes are under investigation looking for high yield positronium formation both in reflection and in transmission. This research is strictly connected to the experiments at CERN and at FRMII. (See image of the Trento slow positron beam, below)


• Involved external institutions: CERN, University of Bergen (Norway), University of Bern (Switzerland), ETH Zurich (Switzerland), Kirchhoff Institute of Physics - Heidelberg (Germany), INR Moscow (Russia), Max-Planck-Institut für Kernphysik - Heidelberg (Germany), Laboratoire Aimé Cotton - Orsay (France), Czech Technical University - Prague (Czech Republic), Stefan Meyer Institut - Vienna (Austria), University of Oslo (Norway), Université Claude Bernard - Lyon (France)
• INFN groups: Cosenza, Genova, Milano, Pavia, TIFPA, Trieste
• Principal Investigator: Michael Dose, CERN, for Italy: Gemma Testera (INFN Genova)
• INFN Project: CSN III
• Duration: 2010 - More years


• Local responsible for TIFPA: Roberto S. Brusa
• Involved TIFPA people: Francesco Guatieri, Luca Ravelli, Luca Penasa, Marco Bettonte



Sketch of the AEGIS experiment The apparatuses for the production of the positron pulsed beam and for off-line positronium excitation are indicated. The target for positronium formation is inserted in the 1T region where the antihydrogen will be formed by a charge exchange process.


FRMII in Garching (Germany) The Ps-TOF apparatus: sketch, positron-optics and assembly at the free beam line NEPOMUC.