Researchers from BASE collaboration at CERN, led by RIKEN, have conducted the most precise measurement, so far, of the charge-to-mass ratio of protons and their antimatter counterparts, antiprotons. Their work was carried out using CERN's Antiproton Decelerator, and results were published in Nature on August 13, 2015.
The study of the proton and antiproton properties was done by the BASE collaboration, which includes researchers from RIKEN, CERN, the Max Planck Institute for Nuclear Physics, The University of Tokyo, Johannes Gutenberg University, GSI Helmholtz Centre for Heavy Ion Research, and Helmholtz Institute Mainz.
The scientists got their results during a stringent test of a fundamental property of the standard model of particle physics, know as CPT (charge, parity, time) symmetry. The experiment was set to test if the system would remain unchanged if the fundamental properties responsible for distinguishing between matter and antimatter, would be reversed.
"This is an important issue, because it helps us to understand why we live in a universe that has practically no antimatter, despite the fact that the Big Bang must have led to the creation of both. If we had found violations of CPT, it would mean that matter and antimatter might have different properties—for example that antiprotons might decay faster than protons—but we have found within quite strict limits that the charge-to-mass ratios are the same.", explained Stefan Ulmer, the leader of the research,
The team received antiprotons and negative hydrogen ions, as a proxy for protons from the Antiproton Decelerator. The next step was trapping a single antiproton-hydrogen ion pairs in a magnetic Penning trap and decelerating them to ultra-low energies. Afterwards, they measured the cyclotron frequency of the pairs to determine the charge-to-mass ratio, and compared them to see how similar they were. in total, the scientists measured around 6 500 pairs in 35 days.
The high-precision measurement has four times higher energy resolution than previous measurements of proton-antiproton pairs. "What we found, is that the charge-to-mass ratio is identical to within just 69 parts per trillion.Ultimately, we plan to achieve measurements that are at least ten or a hundred times more precise than the current standard.", said Ulmer.
The research in questions has some implications for the so-called "weak equivalence" principle, as well, as the team used the results to show that within approximately one part per million, antimatter and matter behave in the same way in respect to gravity.
"There are many reasons to believe in physics beyond the standard model, including the mystery of dark matter and, of course, the imbalance between matter and antimatter. These high-precision measurements put important new constraints and will help us to determine the direction of future research.",the BASE member Christian Smorra added.
- "High-precision comparison of the antiproton-to-proton charge-to-mass ratio" - S. Ulmer, C. Smorra, A. Mooser, K. Franke, H. Nagahama, G. Schneider, T. Higuchi, S. Van Gorp, K. Blaum, Y. Matsuda, W. Quint, J. Walz, Y. Yamazaki - Nature (2015) - doi:10.1038/nature14861
Featured image: A resonant superconducting detection inductor. Image credit: RIKEN, Nature article