Protons might be intrinsically charming.

Subatomic particles are made up of three lighter particles known as quarks. Two quarks are known as “up quarks,” and one is a “down quark.” For decades, physicists have speculated that protons could also be home to more massive quarks. These are called “intrinsic charm quarks.”
Charm quarks weigh more than either up or down quarks. Juan Rojo, the theoretical physicist at The Vrije Universiteit, Amsterdam, says it is possible to have a component heavier than the proton itself.

Rojo and his teammates used a combination of theoretical calculations and experimental results to discover the proton’s mysterious charm. Rojo states that measuring this property is crucial to understanding one of the universe’s most fundamental particles.

Physics experts know that proton complexity increases the deeper you probe it. Protons can be observed at extremely high energies as collisions in particle accelerators such as the Large Hadron Collider (LHC), near Geneva.

They contain a motley of non-matter quarks and antiquarks (SN: 4/18/17). These “extrinsic quarks” are formed when gluons, particles that help stick the quarks together inside protons, break down into quark-antiquark pairs.

The proton’s identity is not affected by extrinsic quarks. These quarks are simply the result of how high-energy gluons behave. Charm quarks may also exist in protons at low energies, but they might be more persistent and deep-seated.

Quantum physics doesn’t allow particles to assume a definite status until they’re measured. Instead, they are described using probabilities. There is a slight chance that protons have intrinsic charm. This means there would be two up quarks, a down quark, and a charm and antiquark. Protons aren’t defined as collections of individual particles, so a proton’s mass doesn’t simply sum up its parts. This small probability indicates that the proton doesn’t have the whole mass of antiquark or charm quark, which could explain why it may contain heavier particles.

The team used thousands of measurements taken at the LHC and other particle accelerators to find evidence for intrinsic charm in protons at a statistical level of 3 Sigmas. Researchers report that intrinsic charm quarks hold 0.6 % of the proton’s momentum.

A conclusive result usually requires 5 Sigma. Ramona Vogt, the theoretical physicist at Lawrence Livermore National Laboratory in California, said that the data and analysis were insufficient to conclude. She wrote a perspective piece about the study of Nature.

It is difficult to define “intrinsic Charm,” which can be confusingly compared to previous results from different groups. Wally Melnitchouk, a theoretical physicist at Jefferson Lab in Newport News (VA), says that previous studies have shown limits to intrinsic charm because they used different schemes and definitions.

The new analysis includes results from the LHC Collaboration, which resulted in potential measurements with intrinsic charm within the proton on February 25 in Physical Review Letters. C.-P. Yuan, a theoretical physicist at Michigan State University in East Lansing, says that including this data in the analysis “is what’s novel.” Yuan is not happy with the method of interpreting the data. “It’s not at what we call the state-of-the-art analysis.”

To better understand the LHC and other facilities that smash protons together, scientists need to determine the proton’s intrinsic appeal content and observe the results. Researchers must be able to assess the details of colliding objects.

According to Tim Hobbs, a theoretical physicist at Fermilab in Batavia, future accelerators like the Electron-Ion Collider, which is planned for completion, could provide data that could be used to help solve this problem. “The problem remains with us. It will be challenging.”