Epic Particle Collider Experiment in US Could Reveal How Matter Holds Itself Together

Robert Hofstadter, a Nobel Prize-winning US physicist, and his team shot highly energetic electrons at an extremely small vial of hydrogen at Stanford Linear Accelerator Center. This opened up a new era in physics.
It was believed that protons (which make up an atom’s nucleus) and neutrons (which make up the nucleus of an atom) were the most fundamental particles found in nature.

They were thought to be 'dots in space', without physical dimensions. It became apparent that these particles weren't fundamental and also had an intricate internal structure.

Hofstadter and his colleagues noticed a slight deviation in the way electrons "scattered" or bounced when they hit hydrogen. This indicated that there was more to a nucleus then the dot-like neutrons and protons they imagined.

The world's first experiments at accelerators that propelled particles to extremely high energies saw a paradigm shift in how we understand matter.

We still have a lot to learn about the atomic nucleus and the'strong force' that holds it all together, one of the four fundamental forces of Nature.

The Electron-Ion Collider is a brand-new accelerator that will be built in the next decade at Brookhaven National Laboratory on Long Island, USA. It will work with 1,300 scientists around the globe to improve our understanding of the nucleus.

(Brookhaven National Lab/Flickr/CC BY–NC

Above: A charged atom colliding with an electron can reveal its nuclear structure.

A strange, but powerful force

It was soon clear that the fundamental building blocks for matter were quarks or gluons after the 1950s revelations. These are the components of hadrons, the collective name for protons or other particles.

People often imagine these particles fitting together like Lego. The quarks and neutrons create protons. Then, protons and neutrons combine to make a nucleus. This nucleus attracts electrons to form an atom. Quarks and gluons, however, are not static building blocks.

Quantum chromodynamics is a theory that describes the interaction of strong forces between quarks and gluons. These gluons are force carriers. It cannot however help us analyze the properties of protons. It is not the fault of computers or our theorists. The equations are just unsolvable.

It is important to study the proton experimentally and other hadrons. To understand the force that binds the proton, it must be studied from all angles. The accelerator is the most powerful tool we have for this purpose.

However, when we look at the proton using a collider (a type accelerator that uses two beams), the results we see depend on how deep we look and what we are looking at. Sometimes it appears as three quarks, other times as an ocean full of gluons or as a sea of antiparticles. Antiparticles are almost identical to particles but have the opposite charge and other quantum properties.

While our understanding of matter at the smallest scales has improved greatly over the past 60-years, there are still many mysteries that the tools of today can't fully solve. What is the nature and purpose of the confinement within a hadron of quarks? How did the quasi-massless quarks 1,000 times lighter create the mass of the proton?

We need a microscope capable of imaging the proton and nucleus at the highest magnifications and constructing 3D images of their structure. This is exactly what the new collider can do.

Experimental set up

The Electron-Ion Collider will use a very intense beam electrons as its probe. This will allow it to cut open the proton/nucleus and view the structure within it.

The beam will collide a beam electrons with a beam protons or ions, and then observe how electrons scatter. The world's first ion beam is available.

Even effects that are not easily perceptible, like scattering processes, which are so rare, you can only see them once in a million collisions, will be visible.

These processes will allow me and other scientists to discover the structure of protons, neutrons, and how they are modified by strong forces.

It is possible to also discover what kind of matter is composed of pure gluons, something that has not been seen before.

Experiment scheme. (Brookhaven National Lab/Flickr/CC BY–NC)

The collider can be tuned to a wide range energy levels. This is similar to turning the magnification dial of a microscope. The higher the energy, one can see deeper into the proton/nucleus and can resolve finer details.

Scientists from around the globe are now working together to create detectors. These detectors will be located at two different points in the collider.

The UK has just awarded a grant to three teams to help with aspects of this effort. They will be designing the key components of the detectors, as well as the technology to implement them. These include sensors for precise tracking of charged particles, sensors to detect electrons scattered very close to the beam line, and detectors to measure the direction of spin (polarization) of particles that are scattered in collisions.

Although it could take 10 years for the collider to be fully designed and built it will likely be worth it.

One of the most difficult challenges in Physics today is to understand the proton's structure and the fundamental force that gives birth to more than 99 percent of visible matter in the Universe.

Daria Sokhan is the Blaise Pascal Chair at CEA Saclay France, / Senior Lecturer at School of Physics and Astronomy University of Glasgow.

This article was republished by The Conversation under Creative Commons. You can read the original article.