Scientists measure proton's mass with record precision

Researchers measured the proton's mass at 1.007276466583 atomic mass units -- three times more precise than the currently accepted value.
By Brooks Hays  |  July 21, 2017 at 2:31 PM
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July 21 (UPI) -- A team of scientists from Germany and Japan have recorded the most precise measurement of a proton's mass.

Researchers accomplished the feat by trapping a proton in a super sensitive single particle detector developed at RIKEN's Ulmer Fundamental Symmetries Laboratory in Japan.

The proton is an important building block in atomic nuclei. Thus, quantifying its mass is an essential component of particle physics. The proton's mass influences the movement of electrons, which orbit around the nucleus. The paths of an atom's electrons determine the wavelengths of light absorbed and reemitted by the atom, which defines an element's spectral signature.

Additionally, a more accurate measure of a proton's mass could help particle physicists better understand the relationship between the proton and the antiproton, and in turn, the relationship between matter and antimatter.

The so-called Penning traps used by researchers are capable of trapping single particles, including a proton, using a combination of electric and magnetic fields.

Once inside the Penning trap, the proton oscillates. Different particles oscillated and different frequencies, and these frequencies can be measured and used to calculate the particle's mass.

To achieve a record-precise reading, scientists used a carbon isotope with a mass of 12 atomic mass units as a control for comparison.

"First we stored each one proton and one carbon ion in separate compartments of our Penning trap apparatus, then transported each of the two ions into the central measurement compartment and measured its motion," researcher Sven Sturm said in a news release.

"It allowed us to measure the proton under identical conditions as the carbon ion despite its about 12-fold lower mass and 6-fold smaller charge," said RIKEN scientist Andreas Mooser.

Researchers measured the proton's mass at 1.007276466583 atomic mass units -- three times more precise than the currently accepted value.

Researchers described their feat in the journal Physical Review Letters.

"In the future, we will store a third ion in our trap tower," researcher Florian Köhler-Langes said. "By simultaneously measuring the motion of this reference ion, we will be able to eliminate the uncertainty originating from fluctuations of the magnetic field."

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