Theory of strong interaction confirmed

Causes for Mass Difference between Neutron and Proton First Determined Accurately

Just because the neutron is a little heavier than the proton, atomic nuclei have exactly the properties that make our world and ultimately our existence possible. © Bergische University Wuppertal
Read out

Decisive difference: If the proton were not a little lighter than the neutron, our universe would look completely different. How this tiny mass difference comes about, researchers have now calculated exactly for the first time. The result confirms the theory of strong interaction and shows how finely tuned our universe is down to its smallest building blocks, according to the physicists in the journal "Science".

The existence and stability of atoms depends crucially on the fact that neutrons are slightly heavier than protons. The experimentally determined masses differ only by about 1.4 parts per thousand. If the difference were only a little different, it would result in a completely different universe with too many neutrons, too little hydrogen or a lack of heavy elements.

Quark movements and charge effects

The reason for the tiny differences lies in the quarks, the building blocks of the protons and neutrons: protons consist of two so-called up quarks and one down quark, while neutrons contain only one up quark, but two down quarks. Above all, the movement of these quarks ensures according to Einstein's formula E = mc2 for different masses. So far it has not been clear to what extent this tiny difference is compensated by interactions with the charge of the proton.

Zoltán Fodor from the University of Wuppertal and his colleagues have now calculated the tiny mass difference and their occurrence in the most accurate way so far. Their new class of simulation combines the laws of quantum chromodynamics with those of quantum electrodynamics to accurately capture the effects of electromagnetic interactions. The time-consuming calculation was made possible with the help of the supercomputer JUQUEEN at Forschungszentrum Jülich.

Accuracy of more than five sigma

In fact, the researchers were able to calculate the factors that produce the tiny mass difference. The results confirm that the difference of 0.14 percent is due to a combination of quark motion and electromagnetic interaction. According to the researchers, the accuracy is five sigma - which means that the result is correct with a 99.9999 percent probability. display

And the calculations show something else: "They provide an insight into the extent to which these constants of nature are finely tuned to create a universe like ours, " said Fodor and his colleagues. The results, however, also trigger the T r to a new generation of simulations that can be used to determine the properties of quarks, gluons, and core particles.

"In the future, the standard model of elementary particle physics could be put to the test with tenfold precision, " explains K lm n Szab from Forschungszentrum J lich. "We have a great opportunity to find effects that point to new physics beyond the standard model." (Science, 2015; doi: 10.1126 / science.1257050)

(Forschungszentrum J lich, 30.03.2015 - NPO)