Yoko’s artist impression
ARSCIMED/Science Photo Library
Protons are more elastic than we thought, according to new measurements. But physicists are divided on whether this anomaly will persist in future measurements, or whether our basic understanding of the proton’s structure needs to change.
A proton contains three small particles called quarks, which are held together by other particles called gluons and “virtual” particles with very short lives. When a proton is exposed to an electric or magnetic field, these internal components move around according to the charge, deforming or stretching the proton.
The extent to which a proton can be stretched in this way is determined by its electrical and magnetic polarizabilities. These two quantities of her, measured many times, tell us about the internal structure of the proton. One of the first of these measurements, made in 2000, looked at the smaller part of the proton and found that it became temporarily more elastic in response to magnetic and electric fields, then stiffened and less deformable. got it.
However, these results are imprecise, and recent experiments disagree, finding protons stiffen when zoomed in on small areas. This is also what the standard model for protons predicts.
now, Nikolaos Sparveris Temple University of Pennsylvania and his colleagues have measured the stretchability of protons with greater precision and, as in the 2000 result, at certain length scales they are highly stretchable to both electric and magnetic fields. I also discovered that
By collecting more data, “we can see it with greater precision,” says Sparveris. “So the ball is now on the side. [standard model] hypothesis. “
To measure proton stretching, Sparveris and his team fired a low-energy electron beam at a liquid hydrogen target. In their setup, when an electron passes a proton in hydrogen, it creates a photon that distorts the proton, effectively an electromagnetic field. By measuring how electrons and protons scatter against each other, the team can calculate how much each proton is distorted by each photon.
The anomalous results look similar to the 2000 study, but with less than half the magnitude of the effect. Judith McGovern at the University of Manchester, England. In general, it is very difficult to measure the polarizability of protons at low energies with high precision, and current theories have no clear explanation for why they spike like Sparveris’ results, she says. “I don’t think most people are taking [the 2000 result] Really seriously, I think they thought it was gone.To be honest, I think most people still assume it’s gone.
Various future experiments, such as using beams of positrons, the antimatter counterpart of electrons, could reveal whether the anomaly really exists, McGovern said. Sparveris and his team plan to conduct further experiments. “We need to rule out the possibility that this is due to experimental parameters or artifacts, so we plan to go back and do more measurements,” he says.
However, if the anomaly remains, we need to revise our understanding of proton structure. “Whether this is of experimental origin will be elucidated by other measurements, but there appears to be a genuine discrepancy between theory and experiment.” Juan Rojo at the Free University of Amsterdam in the Netherlands. “The question is, what does this discrepancy tell us? Specifically, what does understanding these things tell us about proton structure?”
Sign up for Lost in Space-Time. This is a free monthly newsletter about the weirdness of reality.
topic:
