In quantum physics, scientists have solved a mind-bending puzzle about protons

The majority of the visible universe is composed of protons. In a new study published in Nature on August 18, scientists discover that protons can sometimes be made up of particles heavier than themselves due to the peculiar nature of quantum physics.

THE BACKGROUND - Protons are composed of particles called quarks. The six kinds of quarks are as follows. The up, down, and strange quarks are light quarks, lighter than protons. The charm, bottom, and top quarks are heavy quarks, heavier than protons.

In general, protons are believed to consist of two up quarks and one down quark bound together by gluons. The quantum theory of physics, however, suggests that empty space does not exist, not even within protons.

The seemingly empty space is actually buzzing with an infinite number of virtual particles and antiparticles that briefly appear and disappear. In this way, other types of quarks may manifest inside protons besides those that are up and down.

The presence of heavy quarks in protons has been found in previous studies, as well as the presence of strange quarks and strange anti-quarks in protons under normal conditions. It was not known, however, whether heavy quarks were also required to make protons on a regular basis.

This new study was conducted by a team of scientists known as the Neural Network Parton Distribution Function Collaboration. It analyzed data from particle collisions - say, those between two protons or between two electrons. As part of their search, they looked for evidence of charm quarks.

The high energies of particle collisions create extrinsic charm quarks, which do not belong to protons, in the center of collisions. In contrast, intrinsic charm quarks - which were within the protons before collisions - would appear in a faraway location, moving along with the proton they were formerly part of.

As a result of analyzing a massive volume of particle collider data, the scientists found evidence that protons contain intrinsic charm quarks. The proton contains about 0.62 percent of it.

As a particle responsible for a significant portion of the mass in the visible universe and a core component of all matter, the proton, which has been extensively studied for more than 100 years, continues to amaze researchers,' study co-author Juan Rojo, a theoretical particle physicist at Vrije Universiteit Amsterdam, tells Inverse.

'As this remarkable result illustrates, quantum theory always surprises us - we have shown that the proton contains constituents, charm quarks, that are larger in mass than the proton itself.'

The two heaviest quarks of the proton are also intrinsically present in the proton - bottom, with a mass of 4,200 million electron-volts, and top, with a mass of 173,000 million electron-volts.

It is just the beginning of a long-term research program aimed at discovering whether other intrinsic heavy quarks exist in the proton, Rojo explains. The work could take a step towards answering 'one of the major open questions in physics,' he explains.