The Baryon Antibaryon Symmetry Experiment (BASE) experiment at CERN seeks to study the fundamental properties of antiprotons and test the fundamental charge, parity, and time reversal (CPT) invariance. In particular, it aims to precisely measure the magnetic moments of protons and antiprotons to test the limits of the Standard Model. A key aspect of this experiment is the ability to decelerate and trap these particles for long-term study.

A previous version of the experiment employed a vacuum window, transparent to high-energy antiprotons but capable of withstanding atmospheric pressures. A new experimental design requires a thinner window, so Latacz et al. used polyethylene terephthalate (PET) foil to accomplish this.

“When we initiated this project in 2019, there was a scarcity of information regarding the stopping power of antiprotons in PET foils, a lack of tests at cryogenic temperatures, and a dearth of ultra-thin windows,” said author Barbara Latacz. “Starting essentially from scratch, we conducted a comprehensive systematic study of the system, which can benefit not only our research but also that of our colleagues.”

The team found an optimal film thickness of 1760 nm could decelerate antiprotons from 100 keV to 5 keV. An aluminum coating on each side was used to minimize leak rate while securing against foil cracking damage.

The team is excited about the potential applications for this type of vacuum window, which go beyond trapping antiprotons.

“The developments described in this paper will enable the first transport of antiprotons,” said Latacz. “Furthermore, our window technology will be utilized in a CERN spin-off collaboration to reduce air pollution by effectively cleaning exhaust gases emitted by ships.”

Source: “Ultra thin polymer foil cryogenic window for antiproton deceleration and storage,” by B. M. Latacz, B. P. Arndt, J. A. Devlin, S. R. Erlewein, M. Fleck, J. I. Jäger, P. Micke, G. Umbrazunas, E. Wursten, F. Abbass, D. Schweitzer, M. Wiesinger, C. Will, H. Yildiz, K. Blaum, Y. Matsuda, A. Mooser, C. Ospelkaus, C. Smorra, A. Sótér, W. Quint, J. Walz, Y. Yamazaki, and S. Ulmer, Review of Scientific Instruments (2023). The article can be accessed at