A seminar given by
CNRS researcher at the IJCLab (CNRS/IN2P3), Orsay (France)
The rise or fall of antihydrogen: the GBAR* experiment at CERN
Abstract: Since its birth a short century ago, General Relativity, with its cornerstone equivalence principle, has resisted withering experimental scrutiny. Some quantum theories of gravity and models that define physics beyond the standard model include components of the gravitational interaction that are different for matter and antimatter. While this would allow for a difference in their free fall, no experimental test has yet been made to verify this tantalizing possibility. GBAR aims to meet this challenge, probing the equivalence principle for the first time with antihydrogen by dropping it to Earth.
Previous experiments attempting such a test with positrons and antiprotons failed due to the overwhelming influence of residual electromagnetic fields many orders of magnitude stronger than terrestrial gravity. Two other experiments presently running at CERN circumvent this problem by using neutral antihydrogen however the inherent difficulty cooling it limits the eventual precision. The original approach of GBAR is to use stored antihydrogen ions, created from successive atomic charge-exchange reactions. The ions will be cooled sympathetically via laser-cooled Be+ crystals. Once sufficiently cooled, the ion will be neutralized (by photo-detachment) and is subject to Earth’s gravitational field inside a detection chamber.
In 2012, GBAR was accepted by the CERN Research Board (as experiment AD-7) and after development work in Saclay (on positron accumulation, involving one-component plasmas) and in Orsay (on antiproton deceleration), installation of the different components started in 2017. GBAR was the first experiment to receive antiproton beams from the new low-energy storage ring ELENA at the end of 2018.
This presentation will address the physics motivation, describe the experimental components (including the AD facility – unique worldwide) and offer some (modest) initial results on the successful synthesis of antihydrogen in flight.
*Gravitational Behaviour of Antihydrogen at Rest (cern.ch/gbar)