A team of researchers recently reported that they precisely measured the magnetic moment of a proton.
German researchers from the Johannes Gutenberg University, Max Planck Institute for Nuclear Physics, and GSI Helmholtz Centre for Heavy Ion Research, together with researchers from the RIKEN’s Ulmer Fundamental Symmetries Laboratory (FSL) in Japan, just performed a precise measurement of the magnetic moment of a proton.
According to the study published in the journal Science, the experiment conducted by the international team of physicists led them to the exact measurement of 2.79284734462, plus-or-minus 0.00000000082 nuclear magnetons.
The latest finding is said to improve the previously recorded measurement by a factor of 11 and is found consistent with the currently accepted value which is 2.7928473508. It was reported that the level of precision for the latest measurement was less than one part per billion.
Measuring the Magnetic Moment of Proton
For the scientists to perform the measurements, they have to isolate a single proton in the Penning trap. Take note, that’s not two, three, or a handful of protons. Just one proton inside the trap. They were able to do this by detecting the thermal signal of the ions stuck in the trap and manipulate them with an electric field.
“First, we had to isolate a single proton in the trap. We did this by detecting the thermal signal of the ions stuck in the trap, and then using an electric field to eliminate them until we were left with just one,” George Schneider, first author of the paper, said.
In a press release published by RIKEN, they emphasized that the extremely difficult engineering coupled with the ability to transfer the proton between two different traps played a significant role in the success of the experiment. The researchers explained:
“The group’s method for directly measuring the magnetic moment of a particle is based on the fact that a proton in a Penning trap aligns its spin with the trap’s magnetic field. The basic method is to use the detector to measure two frequencies—known as the Larmor (spin-precession) frequency and the cyclotron frequency of the proton in a magnetic field. These can be used to find the magnetic moment.”
Using the Brown-Gabrielse invariance theorem, they were able to measure the cyclotron frequency of the protons. They then measured the Larmor frequency by driving spin flips with the help of radio frequency signals and measuring the probability of a spin flip as a function of the drive frequency.
While the method was already precise, the researchers further boosted it by using the double-trap method which induces the spin transitions in the first trap while they measure the cyclotron frequency. After that, they carefully moved the proton to the second trap where a huge magnetic inhomogeneity detected the spin state. With the high-precision frequency measurement and spin state detection spatially separated, the magnetic moment of the proton was precisely measured.
It took the researcher approximately four months to complete the experiment using three individual protons for a total of 1,264 experiment cycles.
“To move forward in particle physics, we require either high-energy facilities or super precise measurements. With our work we are taking the second route, and we hope in the future to do similar experiments with antiprotons using the same technique. This will allow us to get a better understanding of, for example, atomic structure,” Schneider went on to say.
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