Holy cow, that diet must be working! They’ve just discovered that protons are 4% smaller than they thought!

New Measurement Yields Smaller Proton Radius
Science Daily | November 6, 2019

Using the first new method in half a century for measuring the size of the proton via electron scattering, the PRad collaboration has produced a new value for the proton’s radius in an experiment conducted at the Department of Energy’s Thomas Jefferson National Accelerator Facility.

[The go-to facility when you absolutely, positively have to accelerate either Thomas Jefferson or a National.]

The result, recently published in the journal Nature, is one of the most precise measured from electron-scattering experiments. The new value for the proton radius that was obtained is 0.831 femtometers, which is smaller than the previous electron-scattering value of 0.88 femtometers and is in agreement with recent muonic atomic spectroscopy results.

[So, they’ve got that going for them.]

“We are happy that years of hard work of our collaboration is coming to an end with a good result that will help critically toward solution of the so-called proton radius puzzle,” says Ashot Gasparian, a professor at North Carolina A&T State University and the experiment’s spokesperson.

[. . . who, it turned out, has the most common-sounding name on the team.]

The collaboration instituted three new techniques to improve the precision of the new measurement. The first was implementation of a new type of windowless target system, which was funded by a National Science Foundation Major Research Instrumentation grant and was largely developed, fabricated and operated by Jefferson Lab’s Target group.

The windowless target flowed refrigerated hydrogen gas directly into the stream of the Continuous Electron Beam Accelerator Facility’s 1.1 and 2.2 GeV accelerated electrons and allowed scattered electrons to move nearly unimpeded into the detectors.

“When we say windowless, we are saying that the tube is open to the vacuum of the accelerator. Which seems like a window — but in electron-scattering, a window is a metal cover on the end of the tube, and those have been removed,” says Dipangkar Dutta, an experiment co-spokesperson and a professor at Mississippi State University.

. . .

“The region that we explored is at such a forward angle and at such small four-momentum transfer squared that it has never been reached before in electron-proton scattering,” adds Mahbub Khandaker, an experiment co-spokesperson and a professor at Idaho State University.

. . .

Further, this result also sheds new light on conjecture of a new force of nature that was proposed when the proton radius puzzle first surfaced.

“When the initial proton radius puzzle came out in 2010, there was hope in the community that maybe we have found a fifth force of nature, that this force acts differently between electrons and muons,” says Dutta. “But the PRad experiment seems to shut the door on that possibility.”

Darn it.