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[In] recent decades, physicists have combined strong electric and magnetic fields in a device called a Penning trap to measure the proton's mass more and more precisely. In these experiments, an electric field traps the proton while a magnetic field forces it to move in a circle. While it rotates, the proton will vibrate, or oscillate, at a frequency that's related to its mass. Researchers can calculate the proton's mass by measuring these oscillations, and comparing them to those of a reference—typically, the nucleus of a carbon-12 atom, which is defined as 12 atomic mass units.
But no experiment is perfect. Magnetic fields vary in time and space, causing small measurement errors. To reduce the impact of these fluctuations, a group of physicists working in Mainz, Germany, loaded the carbon nucleus and the proton into separate storage traps, then shuttled them quickly into and out of the measurement trap. Although swapping the nucleus and the proton required more than 30 minutes in previous experiments, the German group needed only about 3 minutes—limiting the chances for errors to accumulate. The team also added more motion detectors to their setup, leading to a measurement with an overall precision of 32 parts per trillion.
The researchers found the mass to be 1.007276466583 atomic mass units [DOI: 10.1103/PhysRevLett.119.033001] [DX]. That's roughly 30 billionths of a percent lower than the average value from past experiments—a seemingly tiny difference that is actually significant by three standard deviations, the team reports this week in Physical Review Letters. (By comparison, scientists typically consider two standard deviations enough for an experimental result to be statistically significant.)
(Score: 4, Informative) by maxwell demon on Friday July 21 2017, @06:49AM (5 children)
Neutrons have the peculiar property of being electrically neutral (thus the name). A penning trap, as mentioned in the summary, uses strong electric fields to trap the particle. An electrically neutral particle doesn't react to electric fields (well, at least not the way electrically charged particles do), that's the definition of "electrically neutral". Therefore this experiment cannot be used to measure the mass of the neutron.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Friday July 21 2017, @07:11AM (4 children)
Not even any mention of indirect measurement involving the mass of a deuteron. Damn crap article.
(Score: 2) by c0lo on Friday July 21 2017, @11:46AM (3 children)
With a poor estimate of the binding energy of a deuterium nucleus, measuring its behaviour wouldn't have bring more precision in the mass of the neutron.
Write a better one.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 0) by Anonymous Coward on Friday July 21 2017, @04:57PM (2 children)
The mass of the neutron has been calculated that way. [wikipedia.org] In a 1986 experiment [aps.org] the binding energy was measured to eight significant digits, so that the neutron's mass could be calculated with ten significant digits. I wouldn't call that "poor."
(Score: 3, Disagree) by c0lo on Friday July 21 2017, @10:06PM (1 child)
TFA abstract [aps.org]
When the correction to the mass of proton is in parts per trillion (32*10-12), I would consider having to use other data with a 10-8 precision as poor.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 0) by Anonymous Coward on Saturday July 22 2017, @08:27AM
From the abstract I linked: "We note that the uncertainties in the neutron-mass data are now dominated by uncertainties arising from mass spectroscopy." The measurement of the binding energy, which makes up about one part in 103 of the deuteron's mass, wasn't the limiting factor.