Journey into the abysses of the atomic nucleus
What gives protons and neutrons their mass and spin? In search of answers, physicists want to use a new particle accelerator to take a much closer look at the subatomic world.
The observable universe contains a roughly staggering 1053 kilograms of normal matter. The lion's share of their mass is contributed by around 1080 protons and neutrons. Together with the much lighter electrons, they form the building material of all atoms and molecules. But where does the mass of the nuclear particles come from?
Finding an answer to this question is proving surprisingly difficult. One thing is clear: the protons and neutrons, also known as nucleons, consist of so-called quarks. These are connected to each other by massless gluons. But the quarks in the nucleons make up barely one percent of their total mass
The possible origin of the oversized residue is just one of several mysteries surrounding the building blocks of atoms. The quantum-mechanical sense of rotation ("spin") of the nucleons is similarly inexplicable - the spin of the quarks inside them is not sufficient for this. Scientists now think that spin, mass and other properties of nucleons have their origin in the complex interaction of quarks and gluons. So far, they don't know how that happens. Theory isn't very helpful at this point.
The researchers are hoping for new experimental data to make progress. This is where a proposed accelerator called the Electron-Ion Collider (EIC) comes into play. It differs from the Large Hadron Collider (LHC) at CERN near Geneva or the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory on Long Island in the USA, in which atomic nuclei made up of many elementary particles collide. Instead, electrons that have no internal structure should collide with protons and neutrons in the EIC. In this way, fewer particles are involved in the interactions. Scientists can use it to better break down the processes and take a clearer look inside the nucleons …
