CERN’s Antimatter Factory is the only place in the world where low-energy antiprotons – the antimatter counterparts of protons – are produced. But in the not-so-distant future it could also be the first place to dispatch trapped antiprotons to another location. On 17 March 2021, the CERN Research Board approved the development of two new experiments to carry antiprotons from the Antimatter Factory to other facilities, for antimatter and nuclear-physics studies. BASE-STEP and PUMA, as the experiments are called, are compact enough to be transported in a small truck or van.
BASE-STEP is based on the BASE experiment – a set-up of traps to store and study in detail antiprotons produced at the Antimatter Factory. Using this set-up, the BASE team measures the properties of the antiproton and compares them with those of the proton to see if there are differences between the two – if found, such differences could shed light on the imbalance between matter and antimatter in the universe. BASE has been performing ever more precise antiproton measurements, but the precision of these measurements is limited by disturbances to the set-up’s magnetic field caused by the magnetic environment of the Antimatter Factory.
BASE-STEP is a variant of the BASE set-up that has been designed to be carried to a facility at CERN or elsewhere, one that has a calmer magnetic environment and thus allows higher-precision measurements to be made. The device will feature a first trap to receive and release the antiprotons produced at the Antimatter Factory and a second trap to store the antiprotons.
PUMA is based on a different transportable antiproton trap system and has a different scientific goal. It will transport antiprotons from the Antimatter Factory to CERN’s nuclear-physics facility, ISOLDE, for investigation of exotic nuclear-physics phenomena. It will consist of a first trapping zone to stop antiprotons, and a second trapping zone to host collisions between the antiprotons and radioactive atomic nuclei that are routinely produced at ISOLDE but decay too rapidly to be transported anywhere themselves.
Analysis of the outcome of these collisions, which will be detected by a particle detector surrounding the collision zone, will help researchers determine the relative densities of protons and neutrons at the surface of nuclei. These densities could reveal whether the nuclei have exotic properties such as thick neutron “skins” or extended halos of protons or neutrons around their core. Such knowledge could shed light on the interior of neutron stars.
PUMA and BASE-STEP are expected to be operational in 2023.