Precise new measurement of proton size indicates a problem, a decade long, may now have a solution.
The proton may be the most important particle in our daily lives, forming one of the three major components of atoms and determining the identity of the elements. This makes the values of its various properties extremely important. Experimental disagreement about one of these properties, called charge radius, has begun a decade of increasingly precise measurements. Scientists have now released the results of a new measurement method and they suggest that uncertainty is nearing an end.
Scientists measure the size of a proton using a value called charge radius, a measure of the distribution of electric charge in a particle. Until 201
But two measurements in 2010 kind of ruined everything. Both measured the lamb displacement of an atom consisting of a proton and a muon, which is something like a heavier, rarer version of the electron. The muon sits much closer to the proton than the electron, which makes the method more accurate. Both results agreed with each other and were much smaller than previous measurements, about 0.842 femtometers – in fact, so small that some physicists wondered if there were undetected physical effects to explain the difference.
"Maybe down the road, if there's new physics, we can figure it out. ”
Physicists continued to measure the charge radius in the 2010s. Back then, earlier this year the puzzle seemed solved without any unexpected new physics. A team from the University of York in Canada, led by Professor Eric Hessels, is observing a more difficult-to-measure Lamb shift, using a hydrogen atom consisting of both a proton and an electron, as well as a lamb displacement of a proton and muon atom, AND the two measurements agreed, and the team measured a radius of charge of .0833 a fetometer. There may be something wrong with measurements from before 2010.
But this is science and puzzles are not solved with single works – other experiments have been underway and usually scientists want to see an independent check of important measurements. Today, another team of scientists working in the United States, Ukraine, Russia and Armenia, forming the PRad collaboration at Jefferson Lab in Virginia, reviewed the measurement using a new proton-electron scattering experiment. "We have decided to create a new type of experiment to tackle the problem of a whole new approach," said Ashot Gasparian, a professor at A&T North Carolina State University and a PRad spokesman at Gizmodo.
The experiment consists of an electron beam of cryogenically cooled hydrogen gas, followed by a series of detectors that measure where electrons end up after scattering, as well as their energies, and finally a hole through which the undegraded electrons pass. This measurement is improved in previous scattering experiments by measuring electrons only slightly scattered by protons, and it uses different detectors to measure electron energy. Various other strategies for increasing the accuracy of the experiment have included sensing electron scattering by themselves and constructing a hydrogen gas container without inlet and outlet windows, which can produce additional noise.
Scientists were able to derive another radius measurement: 0.831 femtometers, in agreement with the Hessel measurement, according to the new book published in Nature.
"In my opinion, after this experiment, the problem is closed," Krzysztof Pachuki, a professor at Warsaw University who told the new study but was not involved in it, told Gizmodo.
What went wrong back in 2010? How has a measurement overturned decades of previous measurements? It's not clear yet, Pachuca said. Perhaps another incorrect value has penetrated the mathematics used to convert the data into the measurement of the proton radio. The final solution to the radius problem will require us to understand whether something is wrong with these past experiments and what it was, physicists Jean-Philippe Carr of the University of Sorbonne and Dominic Marshand are at the University of Paris-Court, written in of nature for the new work.
The authors behind this document do not think that the problem is completely resolved (I want to say what kind of scientist would come out and say, "The problem I am working on is made, now I do not have to work on it anymore." ?). Several more experiments will join the PRad experiments, looking for new ways to increase accuracy and confirm the lower value. And even if people agree on value, perhaps more accurate measurements will reveal other discrepancies within the charge radius, slightly beyond the capabilities of current experiments. You will continue to see these kinds of precise measurements in particle physics, such as the Muon g-2 experiment, as researchers looking for new discrepancies that might hold the key to undiscovered physics.
"What we wanted to do was really push the limit on the accuracy of this type of measurement," Haiyan Gao, a professor at Duke University and PRad spokesman, told Gizmodo. "Maybe down the road, if there's new physics, we can discover it."