Protons could contain a particle smaller and heavier than the proton itself

New research reveals that protons may have more "charm" than previously believed.

One of the subatomic particles that makes up the nucleus of an atom is the proton. Protons are incredibly small, but even smaller elementary particles called quarks form protons. Quarks can be classified into higher, lower, strange, lovely, lower and higher "flavors" or types.

A proton is normally thought to be composed of two up quarks and one down quark. But according to a recent study, it's more complicated than that.

In protons you can also find a charm quark, an elementary particle 1.5 times more massive than the proton itself. Even stranger, even when the charm quark is present in the proton, the heavy particle only has about half the mass of the proton.

The discovery is based entirely on the probabilistic realm of quantum physics. Despite being heavy, the charm quark has a low probability of being in a proton, so its large mass and low probability essentially cancel each other out.

Or, to put it another way, even though the charm quark is present, the proton does not absorb all of the quark's mass, according to Science News.

Protons are extremely complex despite being vital to the structure of atoms, which make up all matter.

Physicists do not know the underlying composition of protons. Stefano Forte, a physicist at the University of Milan, said on the Nature Briefing podcast that quantum physics predicts that additional quarks, in addition to the up and down quarks already known to exist, could occasionally appear in protons.

The latest study demonstrating the existence of the charm quark in protons was co-authored by Forte and appeared in the journal Nature on August 17.

There are six different types of quarks. There are three elements that are heavier than protons and three that are lighter. To determine whether a proton could carry a quark heavier than itself, physicists chose to start with the charm quark because it is the lightest of the heavy ones. They did this by applying a new perspective to 35 years of data on particle destruction.

At particle accelerators like the Large Hadron Collider, the world's largest atom collider near Geneva, scientists hurl particles at each other at breakneck speeds to learn about the structure of subatomic and elementary particles.

These records of particle destruction, dating back to the 1980s, were acquired by researchers in collaboration with the nonprofit organization NNPDF. They include illustrations of experiments in which photons, electrons, muons, neutrinos, and even other protons collided with protons.

Researchers can reassemble the initial state of the particles by examining debris related to the collision.

In the new study, the researchers fed all of this crash data to a machine learning system designed to look for patterns without considering the potential appearance of the structures.

The algorithm returned the possible structures and their probability of existence.

According to Nature Briefing's Forte, the study showed a "small but not negligible" chance of discovering a charm quark. The results constitute the "first solid evidence" that the charm quark could exist, according to Forte, although the amount of evidence was not enough for the researchers to declare the irrefutable discovery of the charm quark in protons.

Forte said the proton's structure is important because, to find new elementary particles, physicists will need to find small discrepancies between what theories predict and what is actually observed. This requires extremely precise measurements of subatomic structures.

For now, physicists still need additional information about the elusive "charm" inside a proton. Future research could be useful, according to Tim Hobbs, a theoretical physicist at Fermilab in Batavia, Illinois. Future research could include the electron-ion collider at Brookhaven National Laboratory in Upton, New York, which is planned to be built.

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