Antimatter annihilation detection with AEgIS

AE ̄ gIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is an antimatter exper- iment based at CERN, whose primary goal is to carry out the first direct measurement of the Earth’s gravitational acceleration on antimatter. A precise measurement of antimatter gravity would be the first precision test of the Weak Equivalence Principle for antimatter. The principle of the experiment is based on the formation of antihydrogen through a charge exchange reaction between laser excited (Rydberg) positronium and ultra-cold antiprotons. The antihydrogen atoms will be accelerated by an inhomogeneous electric field (Stark acceleration) to form a pulsed cold beam. The free fall of the antihydrogen due to Earth’s gravity will be measured using a moiré de- flectometer and a hybrid position detector. This detector is foreseen to consist of an active silicon part, where the annihilation of antihydrogen takes place, followed by an emulsion part coupled to a fiber time-of-flight detector. This overview presents the current results from the R&D; efforts for the construction of the silicon position detector. Low energy antiproton annihilations in silicon were studied in detail using different silicon sensor technologies. A first comparison between experimental data and Monte Carlo simulations for low energy antiproton annihilation is also re- ported, suggesting areas where the improvement of simulation models is possible. The outcome of these tests defined the basis for the final design parameters of the silicon position detector. This detector will consist of a 50 m m thick silicon strip sensor bonded to an application specific integrated circuit (ASIC) with self-triggering readout capabilities and a timing resolution in the order of m s