BASE – Testing Fundamental Symmetries By High Precision Comparisons Of The Fundamental Properties Of Protons And AntiprotonsONLINE ONLY

BASE is an international collaboration focused on testing CPT invariance by performing ultra-precise measure-ments of the fundamental properties of antibaryons and baryons. In this seminar, we will focus on our flagship experiment at CERN which is dedicated to measure the antiproton and proton magnetic moments. To date, the measurement record for these quantities is at the fractional resolution of 1.5 p.p.b. [1] and 300 p.p.t. [2], respectively. We will report on the status of the current measurement campaign with the goal to improve the fractional accuracy of the antiproton magnetic moment by at least a factor of 10. An important ingredient is the development of a new cooling trap, which provides orders of magnitude improved cyclotron-mode cooling which resulted in error-free, non-destructive antiproton spin quantum transition spectroscopy [3]. Additionally, we will present the first implementation of coherent spin-state spectroscopy of a single antiproton spin, enabling measurements at sub-200mHz line-width and >70% inversion,16-fold narrower and 1.5 time higher than in previous experiments [4]. Finally, we will summarize the status of improved measurements.

Currently, the precision of our experiments is limited by magnetic noise in the accelerator hall. To overcome this limitation, we have developed an open Penning trap system, BASE-STEP [5], which will enable the transport of antiprotons to dedicated offline laboratories at Heinrich Heine University Dusseldorf and CERN. In the stable environment of these new laboratories, we aim to achieve measurements at 100-fold improved precision. We will report on the progress towards the first transport of antiprotons, and the first successful demonstration of proton transport [6], that has the transformative potential for the future of the entire antimatter program.

[1] C. Smorra, et al. "A parts-per-billion measurement of the antiproton magnetic moment." Nature 550.7676 (2017): 371-374.
[2] G. Schneider, et al. "Double-trap measurement of the proton magnetic moment at 0.3 parts per billion precision." Science 358.6366 (2017): 1081-1084.
[3] B. M. Latacz, et al. "Orders of Magnitude Improved Cyclotron-Mode Cooling for Nondestructive Spin Quantum Transition Spectroscopy with Single Trapped Antiprotons." Physical Review Letters 133.5 (2024): 053201.
[4] https://www.researchsquare.com/article/rs-6198926/v1 Nature, accepted for publication.
[5] C. Smorra, et al. "BASE-STEP: A transportable antiproton reservoir for fundamental interaction studies.Review of Scientific Instruments 94.11 (2023).
[6] M. Leonhardt, et al. "Proton transport from the antimatter factory of CERN." Nature, 641(8064), 871-875 (2025).

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