Slow Neutral Antimatter Atoms in Excited States for Inertial-type Precision Measurements (SNAP)

The Antiproton Decelerator (AD) facility at CERN became operational in 2000 and is presently the only facility in the world to allow the realization of experiments with low energy antiproton beams. It has led to the successful production of cold antihydrogen, which has been widely acknowledged in the scientific community, as well as in the public media.

The successful storage of antihydrogen over an extended period was selected as top physics highlight in 2010 by physics world. Other more recent breakthroughs include the production of antihydrogen for in-flight hyperfine spectroscopy , direct measurements into the antihydrogen charge anomaly , observation of the 1S-2S transition in trapped antihydrogen and its characterization, the observation of the 1S-2P Lyman-alpha transition in antihydrogen, the demonstration of novel cooling techniques, the precise measurement of the antiproton-to-proton charge-mass ratio, and studies into high-resolution laser resonances of antiprotonic helium in superfluid 4He.

The here-proposed project SNAP aims at developing slow beams of neutral antimatter atoms for cutting-edge antimatter physics research. The AEgIS collaboration, located at the AD, has the primary goal to directly measure, for the first time, the effect of gravity on antihydrogen with significant precision. Indirect bounds that assume the validity of, for example, the universality of free fall, the Weak Equivalence Principle or the CPT invariance also in the case of antimatter constrain an anomalous gravitational behaviour to a level where only precision measurements can operate. Vice versa, antimatter experiments with sufficient precision are essential to validate these fundamental assumptions. By creating nanostructured silicon membranes with few micrometer thickness, a geometrically optimized positron-to-positronium converter will be used to efficiently form a Ps beam in cryogenic UHV environments. Making use of AEgIS' two established laser systems for Ps excitation, we will then attempt Ps laser cooling for the first time. The successful application of laser cooling will enable us to create the world-wide coldest Ps beam with an outstanding intensity.

This beam will be immediately applied to two ambitious research agendas:

The first is AEgIS' flagship goal to perform the charge exchange reaction between cold antiprotons from the new ELENA facility and AEgIS' intense cold Ps beam to create a pulsed source of antihydrogen with unprecedented intensity.

The second is the systematic study of excited neutral Ps atoms passing through a matter grating. Such gratings are the central piece of a so-called Moire deflectometer, essentially an atomic interferometer operating in the classical regime. The deflectometer enables the detection of the displacement of neutral atoms due to gravity with the required precision, the main uncertainty being the influence of the grating's surface dipole potentials. We thus apply our cold Ps beam to study the effect of van-der-Waals forces of the matter grating on neutral excited atoms, exploiting the unique property of the matter-antimatter compound system to annihilate after a well-defined time or upon collision into its signature annihilation particles, carrying information about the interaction with the gratings.