Shining light on the inner details and breakup of deuterons

Scientists have found a way to “see” deuterons, the simplest atomic nuclei, to better understand the “glue” that holds the building blocks of matter together. The new results come from collisions of photons (particles of light) with deuterons, which are made of just one proton bonded to one neutron. In these collisions, the photons act like an X-ray to provide a first glimpse of how particles called gluons are arranged in the deuteron. These collisions can also tear the deuteron apart, providing insight into what holds the proton and neutron together.

By studying the deuteron, the simplest nucleus in nature, scientists gain insight into the more complex atomic nuclei that make up essentially all visible matter in the universe. This research on deuterons helps explain how nuclei form from quarks and gluons, and how the masses of nuclei are generated dynamically by gluons. Deuterons also play an important role in energy production in the sun, which starts with two protons merging into a deuteron. Studying deuterons can help scientists better understand fusion reactions. This could lead to strategies for harnessing fusion energy to make electricity on Earth.

In this work, scientists from the STAR collaboration looked at existing data from deuteron-gold collisions at the Relativistic Heavy Ion Collider (RHIC), a Department of Energy (DOE) user facility. At RHIC, researchers can use photons surrounding fast-moving gold ions to investigate the role of gluons. By studying the gluon dynamics in the deuteron, the simplest atomic nucleus, scientists gain insight into how the distribution and behavior of gluons, as force-carrying particles, change as nuclei become more complex. In the RHIC collisions studied in this work, scientists used the STAR detector to track how much momentum was transferred from gluons in the deuteron to particles created in these interactions. Because that momentum transfer relates to where the gluons are in the nucleus, the scientists used the data to map the gluon distribution in the deuteron. In addition, any photon-gluon interaction also bends the deuteron — and sometimes breaks it apart. STAR tracked “spectator neutrons” emerging from this rift to learn more about how gluons hold these nuclei together.

Understanding the role of gluons in nuclear matter will be a focus of the Electron-Ion Collider (EIC), a new facility that is in the planning stages at Brookhaven National Laboratory. EIC will use photons generated by electrons to investigate the gluon distributions in protons and nuclei, and to study the force that holds protons and neutrons together to form nuclei.