AEgIS Experiment : measuring the acceleration g of the earth’s gravitational field on antihydrogen beam

The AE (g$) over bar IS experiment [1] aims at directly measuring the gravitational acceleration g on a beam of cold antihydrogen ((H) over bar) to a precision of 1%, performing the first test with antimatter of the (WEP) Weak Equivalence Principle. The experimental apparatus is sited at the Antiproton Decelerator (AD) at CERN, Geneva, Switzerland. After production by mixing of antiprotons with Rydberg state positronium atoms (P-s), the (H) over bar atoms will be driven to fly horizontally with a velocity of a few 100 ms(-1) for a path length of about 1 meter. The small deflection, few tens of mu m, will be measured using two material gratings (of period similar to 80 mu m) coupled to a position-sensitive detector working as a moire deflectometer similarly to what has been done with matter atoms [2]. The shadow pattern produced by the (H) over bar beam will then be detected by reconstructing the annihilation points with a spatial resolution (similar to 2 mu m) of each antiatom at the end of the flight path by the sensitive-position detector. During 2012 the experimental apparatus has been commissioned with antiprotons and positrons. Since the AD will not be running during 2013, during the refurbishment of the CERN accelerators, the experiment is currently working with positrons, electrons and protons, in order to prepare the way for the antihydrogen production in late 2014.