Zeroing in on the proton's magnetic moment

May 28, 2014
The quark structure of the proton. There are two up quarks in it and one down quark. The strong force is mediated by gluons (wavey). The strong force has three types of charges, the so-called red, green and the blue. Note that the choice of green for the down quark is arbitrary; the "color charge" is thought of as circulating among the three quarks. Credit: Arpad Horvath/Wikipedia

As part of a series of experiments designed to resolve one of the deepest mysteries of physics today, researchers from RIKEN, in collaboration with the University of Mainz, GSI Darmstadt and the Max Planck Institute for Physics at Heidelberg, have made the most precise ever direct measurement of the magnetic moment of a proton.

The work, published in Nature today, seeks to answer the fundamental question of why we exist at all. It is believed that the Big Bang some 13 billion years ago generated equal amounts of matter and antimatter-which annihilate when they collide-and yet the universe today seems to contain only matter. Work is being carried out from many fronts to detect differences that would explain this, and one promising route is to compare the of particles and their antimatter conjugates, as even a tiny difference could explain the matter-antimatter asymmetry. The research collaboration is working to measure the magnetic moment of the and antiproton to unprecedented precision, and determine if there is any difference.

In the study published today, the researchers reached an important milestone by directly measuring the moment of a single proton to enormous precision, based on spectroscopy of a single particle in a Penning trap. Andreas Mooser, first author of the paper, explains that "this important quantity has never been measured directly and is so far only known at a relative precision of about 10 parts per billion, based on hyperfine spectroscopy of a MASER in a magnetic field. However, this required significant theoretical corrections to extract the proton's magnetic moment from the measurement." In the new paper the researchers report the first direct high precision measurement of the proton magnetic moment at a fractional precision of 3 parts per billion, improving the 42-year-old "fundamental constant" by a factor of three.

The new method using a single particle in a Penning trap can now be directly applied to measure the magnetic moment of the antiproton, which is currently known at a relative precision of only 4 parts per million.

According to RIKEN researcher Stefan Ulmer, second author of the paper and spokesperson of the BASE collaboration at CERN which aims at the high of the antiproton moment, "Using the new method will allow this value to be improved by at least a factor of thousand, providing a stringent test of matter -antimatter symmetry."

Explore further: Magnetic properties of a single proton directly observed for the first time

More information: Direct high-precision measurement of the magnetic moment of the proton, Nature, 2014. DOI: 10.1038/nature13388

Related Stories

The debut of the antihydrogen beam

March 7, 2014

The standard model of particle physics suggests that matter and antimatter are equal and opposite in every way. Yet the observable Universe is made almost entirely of matter—an asymmetry that remains one of the greatest ...

Recommended for you

Using optical fiber to generate a two-micron laser

October 9, 2015

Lasers with a wavelength of two microns could move the boundaries of surgery and molecule detection. Researchers at EPFL have managed to generate such lasers using a simple and inexpensive method.

Perfectly accurate clocks turn out to be impossible

October 7, 2015

Can the passage of time be measured precisely, always and everywhere? The answer will upset many watchmakers. A team of physicists from the universities of Warsaw and Nottingham have just shown that when we are dealing with ...

The topolariton, a new half-matter, half-light particle

October 7, 2015

A new type of "quasiparticle" theorized by Caltech's Gil Refael, a professor of theoretical physics and condensed matter theory, could help improve the efficiency of a wide range of photonic devices—technologies, such as ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (3) May 28, 2014
PDF from the arXiv:
not rated yet May 29, 2014
And we all know it is about 2.79 nuclear magneton, such trivialities should indeed not be mentioned in a post. That would spoil the trade.
May 29, 2014
This comment has been removed by a moderator.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.