Magazine article Science News

Proton's Magnetism Pinned Down: Further Analysis May Reveal Why Universe Lacks Antimatter

Magazine article Science News

Proton's Magnetism Pinned Down: Further Analysis May Reveal Why Universe Lacks Antimatter

Article excerpt

A lone proton's magnetism is pretty weak, yet it's reeling in researchers trying to solve one of the biggest mysteries in physics.

A new measurement quantifies the feeble intrinsic magnetism of the proton and sets the stage for a similar test of the proton's antimatter counterpart. By comparing this magnetic property of protons with that of antiprotons, researchers hope to gain insight into why the universe is dominated by matter rather than antimatter.

Scientists have a pretty good handle on the proton, but in recent years they have used increasingly sophisticated equipment to probe the particle's basic properties with unprecedented precision. One such property is the magnetic moment, which describes how a particle responds to a magnetic field. "Each fundamental particle behaves like a very tiny bar magnet or compass needle," explains Stefan Ulmer, a particle physicist at RIKEN in Wako, Japan.

Ulmer and his team used a device called a Penning trap to improve on previous magnetic moment measurements for the proton. The trap consists of a small tube emptied of all matter save for a single charged particle--in this case, a proton. Strong electric and magnetic fields lock the proton in place, allowing the researchers to observe the particle responding to subtle changes in the magnetic fields' strength. The new magnetic moment figure, published in the May 29 Nature, has three times the precision of the previous best measurement, which dates back to 1972. …

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