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Last June, Jerry Gilfoyle in Physics was elected chair of an international nuclear physics collaboration at the Thomas Jefferson National Accelerator Laboratory (JLab) in Newport News, Va. The group is called the CLAS Collaboration and consists of about 220 physicists from 39 institutions located in twelve countries. Gilfoyle shared some background on the goals of the CLAS Collaboration and some of the science behind the group’s work.

By Jerry Gilfoyle

The mission of the CLAS Collaboration is to build, commission, and operate a large particle detector at JLab. What will scientists do with the particle detector once it’s built? Scientists have known for many decades that most of the stuff around us (at least the mass of it) is made of particles called quarks. Electrons are in there too, but their mass is small. The quarks combine to form protons and neutrons, which in turn, bind together to form atomic nuclei like carbon, oxygen, and iron. Other weird particles called gluons pop in and out of existence in a bubbling soup inside the nucleus and, strangely enough, create the force that holds the quarks together.

It is this so-called ‘strong force’ that poses one of the great challenges to our understanding of the Universe. Every other fundamental force we observe gets weaker as two particles get farther apart. This feature allows us to launch spacecraft to other planets and to generate electricity. The strong force that binds quarks together is different. It is constant regardless of the distance between them. Pull two quarks a centimeter apart and the force between them is the same as when they are 10,000,000,000,000 times closer (like in a proton).

The strong force is one of the great unsolved problems in science and understanding it remains a grand challenge. If you can figure it out you will even get a prize – $1,000,000 from the Clay Mathematics Institute!

CLAS12 under construction

How is the JLab attempting to solve the problem? The central scientific instrument at JLab is the Continuous Electron Beam Accelerator Facility (CEBAF), a mile-long, racetrack-shaped accelerator that pushes electrons close to the speed of light. It’s a large electron microscope that illuminates the interior of protons and nuclei. JLab is in the final stages of a $340-million upgrade to increase the power of the machine and the CLAS Collaboration will bring a new detector on-line in the next fifteen months.

That device is called CLAS12 and will measure the debris from collisions of the electron beam with those protons and atomic nuclei. It is a big (about 10 meters high), expensive ($50-million) device built by the CLAS Collaboration. To capture enough information to learn about quarks and gluons requires many different layers of technologies to detect the passage of the debris through CLAS12 and turn that information into electronic signals that we gather, collate, and save.

There are more than 60,000 components in CLAS12. When we start running we will record the data from about 10,000 collisions each second collecting 5-10 terabytes (1 terabyte = 1000 gigabytes) each day. My Richmond students and I are developing the algorithms and code to simulate, calibrate, and analyze this deluge of data when it comes in 2017. This data will hopefully give us the clues to unravel the mysteries of the strong force.

Who pays for all this? JLab is a national lab funded by the US Department of Energy and the American taxpayer. What you and the country get in return is an army of young scientists and technicians trained at the frontier of science. The new knowledge created at JLab will be carried by these scientists into industry, academia, and government to tackle the array of challenges we face. Economists tell us that half or more of our growth in standard of living comes from new knowledge and technology. That new knowledge is brewed up today in places like JLab.

Photo captions:

Top: Richmond students tour the CLAS12 detector under construction at JLab. They stand on a superstructure that supports the central part of CLAS12. One of the layers of the forward component of CLAS12 can be seen behind them (the large triangles with the red and black coverings).

Bottom: CLAS12 under construction. Part of the particle detector being built by the CLAS Collaboration is shown being assembled. The large, triangular boxes will measure the energy of electrons, protons, and other debris from collisions of the electron beam (which enters from the left) with the target. The target will be placed roughly where the worker in the boom lift is located in the picture. The photo shows only a fraction of the final device.