Have you ever wondered about the building blocks of the world around us? From the chair you’re sitting in to the stars in the night sky, everything is made of atoms, which in turn are composed of electrons, protons, and neutrons. But did you know that scientists have long been puzzled over the size of the positively charged protons? A few years ago, a new measurement technique suggested that protons are smaller than previously assumed, causing a stir among experts and raising questions about the validity of the Standard Model of particle physics. Now, a team of physicists from the University of Bonn and the Technical University of Darmstadt have developed a method that allows for a more comprehensive analysis of older and recent experiments, ultimately revealing that the discrepancy in proton size is likely due to errors in the interpretation of older measurements.
Join us as we delve deeper into this exciting new study, which not only helps us understand the structure of the world around us, but also provides new insights into the fine structure of protons and neutrons.
Scientists at the University of Bonn and the Technical University of Darmstadt have developed a new method that allows them to analyze the results of older and more recent experiments much more comprehensively than before. This has resulted in a smaller proton radius from the older data, which suggests that there is probably no difference between the values, regardless of which measurement method they are based on.
It all started a few years ago when a novel measurement technique showed that protons are probably smaller than had been assumed since the 1990s. This discrepancy surprised the scientific community, with some researchers even believing that the Standard Model of particle physics would have to be changed. But now, the new method developed by the scientists at the University of Bonn and the Technical University of Darmstadt has helped to clear things up.
Our office chair, the air we breathe, the stars in the night sky: they are all made of atoms, which in turn are composed of electrons, protons and neutrons. Electrons are negatively charged; according to current knowledge, they have no expansion, but are point-like. The positively charged protons are different — according to current measurements, their radius is 0.84 femtometers (a femtometer is a quadrillionth of a meter).
To determine the radius of a proton, scientists can bombard it with an electron beam in an accelerator. When an electron collides with the proton, both change their direction of motion — similar to the collision of two billiard balls. In physics, this process is called elastic scattering. The larger the proton, the more frequently such collisions occur. Its expansion can therefore be calculated from the type and extent of the scattering.
The higher the velocity of the electron beam, the more precise the measurements. However, this also increases the risk that the electron and proton will form new particles when they collide. But the scientists have developed a theoretical basis that allows them to take into account data that have so far been left out, such as collisions that produce other particles, and so-called electron-positron annihilation.
Using this method, the physicists reanalyzed readings from older, as well as very recent, experiments. With their method, the researchers arrived at 0.84 femtometers, which is the radius that was also found in new measurements based on a completely different methodology. This suggests that the proton is actually about 5 percent smaller than was assumed in the 1990s and 2000s.
The new method also allows new insights into the fine structure of protons and their uncharged siblings, neutrons. This helps us to understand a little better the structure of the world around us — the chair, the air, but also the stars in the night sky.
In summary, this new method that allows for a more comprehensive analysis of the results of older and more recent experiments has led to a new understanding of the protons, and this new understanding suggests that the proton is actually smaller than previously assumed. This helps us to better understand the structure of the world around us. The study was funded by various organizations such as the German Research Foundation (DFG), the National Natural Science Foundation of China (NSFC), the Volkswagen Foundation, the EU Horizon 2020 program, and the German Federal Ministry of Education and Research (BMBF).
Publication: Yong-Hui Lin, Hans-Werner Hammer and Ulf-G. Meißner: New insights into the nucleon’s electromagnetic structure; Physical Review Letters, https://doi.org/10.1103/PhysRevLett.128.052002