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Researchers Cannot Find Out Why The Radius Of A Proton Is Getting Changing In Every Experiment



In 2010, researchers found a discrepancy in the size of the proton. They took a hydrogen atom and interchanged the electron for a muon (its heavier cousin), and found that for some unidentified reason the radius of the proton contracted. This has been called the proton radius mystery.


The team of researchers has repeated the experiment for an atom of deuterium, an isotope of hydrogen, and once the electron was interchanged for the muon, the researchers detected once again a size discrepancy in the nucleus. This discovery was described in Science.

The muon is an fundamental particle and it is about 200 times heavier than the electron. Being so heavy when, it is put into an atom moves it much nearer to the nucleus than the electron, and its crusade can be used to study the property of particles in the atomic nucleus. But, the astonishing fact is that it should not change the nucleus. Electrons and muons both have the same electric charge, which is what retains them around the nucleus, but that does not disturb the size of the proton. There are a few details flying around to describe this discrepancy. One idea is that we are seeing sign of an unknown force, although that is very doubtful.

The researchers consider the discrepancy might not be in the different measurements, but in the old ones. The earlier measurements of the proton and the deuteron (the nucleus of deuterium) using hydrogen spectroscopy might not have reached the similar degree of precision.

Aldo Antognini co-author from the Paul Scherrer Institute (PSI) in Switzerland said in a statement, “Naturally, it cannot be that the deuteron, any more than the proton, has two different sizes. The mystery could be solved very easily if we assume a minimal experimental problem with the hydrogen spectroscopy."

Since the proton results, laborites around the world have been improving their measuring devices, gaining a more precise measurement. There has not been any verification that the discrepancy is really due to a less accurate measurement, but the team is happy that their finding has directed to this global upgrade. Lead author Randolf Pohl, also from the Paul Scherrer Institute (PSI), added, "If our value had agreed with the previous ones, there would not have been this darned mystery of the proton radius; but there also never would have been this worldwide surge of activity that has led to several highly accurate measurement setups."

Confidently, new measurements will shortly be able to explain if this is a coincidence of the experiments, or some unfamiliar physics at work.

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