BASE CERN
Scope
BASE at CERN is the current flagship experiment of the collaboration. In this experiment, we are using advanced cryogenic Penning trap systems to compare the fundamental properties of protons and antiprotons with high precision. Such experiments test the fundamental charge, parity, time-reversal invariance in the baryon sector. Any measured difference would hint at new physics beyond the Standard Model of particle physics, and potentially shed light in the striking imbalance of matter over antimatter, that is observed on universal scales.
Major Achievements – Matter/Antimatter Symmetry Tests
The collaboration holds the records of comparing the fundamental properties of protons and antiprotons. We have performed the most precise test of CPT invariance in the baryon sector, by comparing the proton and antiproton charge-to-mass ratios with a fractional accuracy at the level of 16 parts in a trillion [read here]. This experiment is based on precision mass spectrometry – comparing antiprotons to negatively charged hydrogen ions – using a fast particle shuttling technique in a multi-Penning trap system. This experiment also provides one to the most stringent tests of the clock weak equivalence principle with antimatter and has potential to constrain additional exotic physics mechanisms.
In addition, we are operating experiments with cutting edge resolution, that compare proton and antiproton magnetic moments. These experiments use single particle quantum transition spectroscopy with a single antiproton spin – watching a single (anti)nucleon flip its spin – to determine the particle’s spin precession frequency. Combining this single particle nuclear magnetic resonance spectroscopy with precision measurements of the particles cyclotron frequency in the trap gives access to the antiproton magnetic moment. This experiment is outstandingly challenging, due to the tiny magnetic moment of the antiproton, being 658 times smaller than that of the electron. It only becomes possible by combining several cutting-edge techniques at fundamental technical limits. For this experiment we use the world’s smallest precision Penning trap, non-destructive particle detectors with world-leading resolution, the world’s most stable power supplies, in the strongest magnetic bottle ever produced in a Penning trap experiment, to use the continuous Stern-Gerlach effect to readout the antiproton spin state. Combining these ideals with multi-trap-techniques, we have measured the antiproton magnetic moment with a fractional accuracy on the parts per billion level. New coherent measurements, supported by a unique cooling trap, a highly homogeneous magnetic field in the precision trap, performing for the first time coherent spin spectroscopy will enable 10 to 100-fold improved measurements of the antiproton magnetic moment. This measurement will constitute the most precise test of CPT invariance with a vector quantity in the baryon sector, being ultra-sensitive to very different extensions of the standard model than the charge-to-mass ratio experiment.
Exotic Physics Tests and Limits
At BASE, we're not just pushing the boundaries of precision with antiproton measurements — we're diving into the frontier of dark matter and beyond! Our team is exploring the mysterious realm of feebly interacting particles like axions and millicharged particles, using cutting-edge Penning trap technology.
Highlights include the first-ever limits on how antiprotons might interact with axion-like dark matter, unveiled by tracking subtle time-based variations in their magnetic moments. We’ve also harnessed our ultra-sensitive superconducting detection systems to probe the coupling between axion-like particles and photons. And when it comes to millicharged particles — hypothetical particles with a tiny electric charge — our heating rate measurements have set the most competitive constraints yet.
These groundbreaking results not only challenge current physics models but also open thrilling new paths toward uncovering the nature of dark matter.
Transformative Future – Antiproton Transport
At BASE, we’re aiming for a quantum leap in precision—by relocating antimatter experiments from the noisy environment of the AD/ELENA hall to a quiet, offline laboratory. Why? Because precision matters. In the accelerator-off season, we’ve achieved groundbreaking measurement stability— record cyclotron frequency scatters and ultra-narrow g-factor resonance signals. But once the accelerators power up, magnetic field noise skyrockets, degrading our measurement accuracy drastically.
This instability dramatically extends the time needed to reach high-precision goals: what takes weeks in a calm lab would require decades in an active accelerator hall. That’s not just inefficient—it makes timely, independent verification of potential physics breakthroughs virtually impossible.
Our Vision
We want to transport antimatter to controlled, noise-free environments where we can push antimatter spectroscopy to new frontiers, improving precision by at least a factor of 100. We've already taken key steps—demonstrating antiproton trapping for decades, experimenting at ultra-low particle consumption rate, and even successful particle transport using our transportable trap system BASE-STEP. Now, we're ready to move BASE to a dedicated offline lab and unlock the full potential of precision antiproton physics.