How is matter held together? A US experiment could solve the mystery

When Nobel Prize-winning US physicist Robert Hofstadter and his team fired highly energetic electrons at a small vial of hydrogen at the Stanford Linear Accelerator Center in 1956, they opened the door to a new era of physics. Until then, it was thought that protons and neutrons, which make up the nucleus of an atom, were the most fundamental particles in nature. They were in fact considered "points" in space, without physical dimensions. But it suddenly became clear that these particles were not fundamental at all and also had a complex internal size and structure.

Yet there is much we still don't know about the atomic nucleus - as well as about the "strong force", a of the four fundamental forces of nature, which holds it together. Now a brand new accelerator, the Electron-Ion Collider to be built within the decade at Brookhaven National Laboratory in Long Island, USA, with the help of 1,300 scientists from around the world, could help bring the our understanding of the nucleus on a new level.

credits: Brookhaven National Lab / Flickr / CC BY-NC After the 1950s revelations, it soon became clear that particles called quarks and gluons are the basic building blocks of matter . They are the constituents of hadrons, which is the collective name for protons and other particles. A theory called quantum chromodynamics describes how the strong force between quarks works, mediated by the gluons, which are force carriers. Yet it cannot help us analytically calculate the properties of the proton.

This is why the experimental study of the proton and other hadrons is so crucial: to understand the proton and the force that binds it, it must be studied from every angle. For this, the accelerator is our most powerful tool. To answer these questions, in fact, we need a microscope able to imagine the structure of the proton and the nucleus through the widest range of magnifications with very high details and build 3D images of their structure and dynamics. This is exactly what the new collider will do.