Scientists gain new insight into how mass is distributed within hadrons

Scientists can determine the mass of elementary particles made of quarks by examining the particle’s energy and momentum in four-dimensional spacetime. One of the quantities that encode this information is called the trace anomaly, which is associated with the fact that the physical observables obtained in high-energy experiments depend on the energy/momentum scales involved.

Researchers believe that trace anomalies are important for maintaining quark bonds within elementary particles.

In a study published in Physical Review D, scientists calculated trace anomalies in both nucleons (protons or neutrons) and pions (subatomic particles consisting of one quark and one antiquark).

Calculations show that for pions, the mass distribution is similar to the charge distribution of neutrons, whereas for nucleons, the mass distribution is similar to the charge distribution of protons.

Understanding the origin of nucleon mass is one of the main scientific goals of the electron-ion collider (EIC). Scientists also want to understand how the mass from quarks and gluons is distributed within hadrons. These are elementary particles, such as protons and neutrons, made up of quarks and held together by strong forces.

New calculations show that mass distributions can be obtained numerically based on first-principles calculations starting from fundamental physical laws. This new approach to calculations will also help scientists interpret data from nuclear physics experiments.

Experiments exploring the origin of nucleon mass are planned at the future EIC at Brookhaven National Laboratory. In these experiments, electron-proton scattering can generate heavy states that are sensitive to the internal structure of protons, especially the distribution of gluons.

By analyzing scattering data, scientists can learn how the masses of quarks and gluons are distributed within the proton. This is similar to how researchers used X-ray diffraction to discover DNA’s iconic double helix shape. Theoretical calculations help scientists understand how mass is distributed among hadrons according to the Standard Model and provide direction for future experiments.

The discovery revealed an important aspect of how mass is spread out within particles such as pions and nucleons. This result suggests that the structure of pions in particular plays a role in linking two properties of the world described by the Standard Model: the existence of an absolute scale and the asymmetry of left- and right-handed quantities. .