Protons may have more “charm” than we thought, according to new research.
A proton is one of the subatomic particles that make up the nucleus of an atom. As small as protons are, they are made up of even smaller particles elementary particles known as quarks, which come in a variety of “flavors” or types: high, low, strange, charm, low, and high. Typically, a proton is thought to be made up of two up quarks and one down quark.
But a new study reveals that it’s more complicated than that. Protons can also contain a charmed quark, an elementary particle that is 1.5 times the mass of the proton itself. Even stranger, when the proton contains the charm quark, the heavy particle still only carries about half the mass of the proton.
Discovery boils down to the probabilistic world of quantum physics. Although the charm quark is heavy, the probability of it appearing in a proton is quite low, so the high mass and low probability cancel each other out. In other words, the total mass of the charmed quark is not absorbed by the proton, even if the charmed quark is there, Science News reported.
Although protons are fundamental to the structure of atoms – which constitute all matter – they are also very complicated. Physicists don’t really know the basic structure of protons. Quantum physics argues that beyond the up and down quarks known to be present, other quarks might appear in protons from time to time, Stefano Forte, a physicist at the University of Milan, told the podcast Nature briefing (opens in a new tab). Forte was co-author of the new paper showing evidence for the charm quark in protons, published in the journal Nature (opens in a new tab) August 17.
There are six types of quarks. Three are heavier than protons and three are lighter than protons. The charmed quark being the lightest of the heavy lot, the researchers wanted to start with this one to find out if a proton could contain a quark heavier than it. They did this by taking a new approach to 35 years of particle destruction data.
Related: Why physicists are interested in the mysterious quirks of the biggest quark
To learn more about the structure of subatomic and elementary particles, researchers launch particles against each other at lightning speeds in particle accelerators such as the Large Hadron Collider, the largest atom destroyer in the world, located near Geneva. Scientists from the nonprofit NNPDF Collaboration have collected this particle data dating back to the 1980s, including examples of experiments in which photonselectrons, muons, neutrinos and even other protons crashed into protons. By examining the debris from these collisions, researchers can reconstruct the original state of the particles.
In the new study, the scientists fed all of this collision data to a machine learning algorithm designed to search for patterns without any preconceived idea of what the structures would look like. The algorithm returned possible structures and the probability that they actually exist.
The study revealed a “small but not negligible” chance of finding a charm quark, Forte told Nature Briefing. The level of evidence was not high enough for the researchers to declare the undeniable discovery of the charm quark in protons, but the results are the “first hard evidence” that it may be there, Forte said.
The structure of the proton is important, Forte said, because to discover new elementary particles, physicists will need to uncover tiny differences between what theories suggest and what is actually observed. This requires extremely precise measurements of subatomic structures.
For now, physicists still need more data on the elusive “charm” within a proton. Future experiments, such as the planned electron-ion collider at Brookhaven National Laboratory in Upton, New York, could help, Tim Hobbs, theoretical physicist at Fermilab in Batavia, Illinois, told Science News.
Originally posted on Live Science.