ColdPbar · Cold antiProtons for Better Antimatter Research

Cold antiProtons for Better Antimatter Research

The discovery of antimatter – the finding that each subatomic particle has a counterpart with the same mass but opposite charge, with which it annihilates on contact – is a landmark in the physics of the 20th century. According to the Standard Model (SM) of particle physics, particles and antiparticles show equivalent physical interactions and dynamics. This symmetry leads to one of the most prominent open questions in physics: Why do we – and everything around us – exist?!? If matter and antimatter are equivalent, we would expect equal amounts of each having been created at the beginning of the universe, followed by immediate mutual annihilation. However, a part of the matter has survived and we live now in a world dominated by matter. This matter-antimatter asymmetry is not explained by the SM. A promising way to study it is by measuring antiparticle properties and compare them with their matter counterparts. Two efforts to that end are currently pursued: investigating the gravitational interaction of antimatter, and performing precision spectroscopy of bound systems containing antiparticles. The AEgIS experiment at CERN pursues both these approaches. It makes use of slow antiprotons provided by CERN’s AD/ELENA complex (Antiproton Decelerator / Extra Low ENergy Antiproton ring). Those are combined with positrons (“anti-electrons”) to form antihydrogen atoms. Antihydrogen atoms can then be used in free-fall experiments to measure their gravitational acceleration, or as starting point to form more complex antiprotonic bound systems that can then be studied spectroscopically. However, the sensitivity – and thus the discovery potential – of these measurements is limited by the thermal motion of antiprotons. In free-fall experiments, the random thermal motion limits the achievable flux of antihydrogen atoms and blurs the atom’s trajectories. In spectroscopic studies, it leads to limited storage time of the particles and Doppler broadening of spectroscopic transitions. The antiproton temperature could be lowered drastically by thermalization with laser-cooled ions. Laser-cooling – a standard technique for neutral atoms and positive ions – however, has never been realized with negative ions (anions). The focus of this project was to progress towards this goal of laser cooling anions to ultimately provide ultracold antiprotons.

Data: CORDIS, © European Union