Protons Might Be Stretchier Than They Should Be, Scientists Reveal
According to recent findings, protons might be stretchier than they should be. However, physicists are split on whether or not this anomaly will remain in future observations and whether or not this means we need to rethink our basic knowledge of the proton's structure.
The proton comprises three smaller particles called quarks, which are bound together by even smaller particles called gluons and extremely fleeting "virtual" particles. When an electric or magnetic force acts on a proton, its charged parts move around inside the proton. This causes the proton to change shape or stretch.
Together, these quarks form the building blocks of the subatomic particles, which are held together by the strong force, the strongest of the known interactions between subatomic particles. The results of recent studies, as reported in Nature on October 19 by physicist Nikolaos Sparveris and colleagues, appear to indicate that quarks react more strongly to an electric field pushing on them than was previously thought.
This finding may indicate that the strong force is weaker than previously thought. It contradicts the accepted theory of elementary particles and the forces that bind them together to form living things and the physical universe. Some physicists are at a loss to explain the outcome, while others are unsure whether they should even attempt it.
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It is certainly puzzling for the physics of the strong interaction, if this thing persists.
- Sparveris from Temple University in Philadelphia said
Sparveris claims that similar elasticity has been seen in the work of other laboratories but that these findings were less compelling. The measured stretchiness was less severe than in prior trials, but the experimental uncertainty was reduced, so the results were more reliable. This supports the idea that protons are more flexible than standard theory says they should be.
Sparveris's group used a stream of low-energy electrons shot at a liquid-hydrogen target to determine the proton's stretch. In this setup, the proton is deformed as an electron goes past it inside the hydrogen, creating a photon and, in effect, an electromagnetic field. The amount that each proton is warped by a photon may be determined by measuring how much electrons and protons scatter away from each other.
Judith McGovern of the University of Manchester, UK, notes that although the anomalous finding seems comparable to the study from 2000, the amount of the impact has decreased by more than half. According to her, it is challenging to get precise measurements of proton polarisabilities at low energies. There is no clear reason in the prevailing theories for why it should spike in this way, as shown in Sparveris's finding.
McGovern suggests that future research employing positrons (an electron's antimatter counterpart) could help determine whether or not this anomaly exists. Sparveris and his group want to conduct more studies.
I don’t think most people took [the 2000 result] really seriously, I think they assumed that it would go away, and, if I’m quite honest, I think most people will still assume that it will go away.
- says Judith McGovern at the University of Manchester, UK
However, if the anomaly persists, our current knowledge of the proton's structure will need to be revised.
Other measurements will elucidate whether or not this has an experimental origin, but it seems to be a genuine discrepancy between theory and experiment. The question is, what does this discrepancy tell us? And, especially, what can we learn about the proton structure by understanding these things?
- says Juan Rojo at Vrije University Amsterdam in the Netherlands
Researchers concluded that protons might be stretchier than they should be while studying the motion of quarks within protons in reaction to electric fields.
The internal particles of a proton shift about when it is subjected to electric and magnetic forces, causing it to distort, although the mechanisms behind this are not fully understood. An uptick in the plot of proton stretching was seen, but only for a certain range of electron energies.