Protons are longer than they should be.
Subatomic particles are made up of smaller particles, called quarks, which are held together by a strong interaction known as the strong force. New experiments seem to show that quarks respond more than expected to an electric field pulling on them, physicist Nikolaos Sparveris and colleagues report on October 19. nature. The results suggest that the force is no less robust than theory predicts.
The discovery conflicts with the particle model of physics, which describes the particles and forces that make up us and everything around us. The result is that some physicists know how to develop — or even try to.
“Indeed, strong interactions are worrying for physicists if the situation persists,” said Sparver, of Temple University in Philadelphia.
Such an extension has been tested in other labs, but not as convincingly, says Sparveris. The dimensions, which he himself collected, were at the lower end than in previous experiments, but also less experimentally uncertain. That gives the researchers confidence that protons are indeed more readily available than theory says they should be.
At the Thomas Jefferson National Accelerator Facility in Newport News, Va., the team explored proton electrons in a target of ultracold liquid hydrogen. Electrons scattered from protons in hydrogen revealed how protons’ quarks respond to electric fields (SN: 9/13/22). The higher the energy of the electron, the deeper the researchers could see into the protons, and the more electrons they revealed about how the strong force inside the proton works.
For the most part, quarks are expected to move when electrical interactions pull particles in opposite directions. But at one point, when the electronic energy was raised, the quarks appeared to respond to the electric field more strongly than theory would have predicted.
But it only happened because of the small electron energy, which caused a bump in the proton drag plot.
“Usually, the behavior of these things is quite, let’s say, light and there are no damages,” Vladimir Pascalutsa, a scientist from the Johannes Gutenberg University of Mainz in Germany.
Pascalutsa says he often likes to give in to awkward problems, but the odd stretch of protons is too sketchy for him to put lead on paper this time. “You have to be very, very inventive to come up with a whole framework that somehow finds you a new effect,” to explain the bump, he says. “I don’t want to kill the buzzer, but remember, I’m pretty skeptical that this thing is going to be a spy.”
It will take more experiments, as the claimants are excited about extraordinary protons protons, says Pascalutsa. He could opt if Sparver hopes to try the experiment again with positrons, the antimatter version of electrons, scattered instead of protons.
A different type of experiment could make protons even stronger, says Pascalutsa. A current study by Paul Scherrer from the Villigen Institute, Switzerland, could do the trick. It uses hydrogen atoms, which have muons instead of electrons that usually orbit the nucleus of atoms. Muons are about 200 times heavier than electrons, and orbit the nucleus of an atom much closer than electrons – offering a closer look at the proton inside (SN: 10/5/17). The experiment involves activating a “muon particle” with lasers rather than scattering other electrons or positrons from them.
“The precision in muon hydrogen experiments will be much higher than anything that can be obtained in scattering experiments,” says Pascalutsa. If traction gets out there as well, then I’ll start looking at this right away.
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