Jefferson Lab's proposed upgrade, from 6 to 12 billion electron volts (GeV), would include adding 10 superconducting cryomodules to the accelerator, an additional arc of magnets to steer the electron beam, and a fourth experiment hall.

The Upgrade will allow Jefferson Lab to pursue with even greater precision its primary mission of studying the basic building blocks of matter: quarks and gluons. In simplest terms, these elementary particles combine to form protons and neutrons, which, together with electrons, make up all the atoms in the universe.

With the 12 GeV Upgrade, scientists plan to address one of the great mysteries of modern physics -- the mechanism that "confines" quarks together. According to a fundamental theory of particle physics, the force that binds quarks together -- the strong force -- is so powerful that no quark can ever be found alone. Until recently, quarks had only been seen in pairs (in particles called mesons) and in triplets (in particles called baryons: protons and neutrons are baryons). But other quark combinations are theoretically possible. For instance, recent experiments have shown evidence of a five-quark particle (dubbed the pentaquark). The new experimental Hall (Hall D) aims to produce exotic or hybrid mesons. These exotic mesons are produced by exciting the gluons, the strong force "glue" that binds two quarks together. Though predicted by theory, many of these exotic mesons have never been seen before, and identifying them and their properties will provide information on the strong force and how it confines quarks.

The Upgrade will also enable scientists to research the fundamental structure of protons and neutrons (collectively called nucleons). It's now known that nucleons are basically made up of three quarks held together by gluons. But nucleons also contain a kind of 'sea' of quarks and gluons that pop into and out of existence. The improved energy and new detectors of the 12 GeV Upgrade will allow scientists to probe how all of these particles interact to determine a nucleon's basic properties - its mass, spin and how it interacts with other particles around it.

Another puzzle of the physics of the atomic nucleus is how protons and neutrons bind together to form the nucleus. One idea is that, when nucleons are close together, the strong force binding quarks together inside a nucleon is so strong that it can leak out, binding it to other nucleons. Another idea is that protons and neutrons swap quarks, and this exchange binds nucleons together. The Upgrade will allow scientists to further study how nucleons interact and determine the mechanism that binds them together.

Finally, an upgraded CEBAF will allow physicists to study the limits of the "Standard Model," a theory that describes fundamental particles and their interactions. So far, tests of this model have shown that it's accurate. The Upgrade will open new opportunities for probing the model's limits. Discovering where it fails will allow physicists to develop ever more accurate and inclusive theories of matter, giving them insights into the fundamental particles that comprise the world around us.

These experiments, and others, contribute to Jefferson Lab's goal to push knowledge of particle physics beyond current theory by studying the properties of fundamental particles, how these particles interact to form matter and what forces mediate these interactions. Upgrade plans call for a continuation of the research programs in all three current experimental halls (Hall A, Hall B and Hall C), as well as the building of a fourth Hall (Hall D).

Secretary of Energy Spencer Abraham named the Upgrade a near-term priority in DOE's "Facilities for the Future of Science" report and cited the project as a "cost-effective way to. provide the capability to study the structure of protons and neutrons of the atom with much greater precision than is currently possible." The Upgrade was listed as a seventh priority in a field of 28 projects cited in the report.

Critical Decision Zero, or CD-0, is the first of five "critical decisions" that govern construction of DOE facilities and projects. The approval allows JLab to proceed with conceptual design of the Upgrade and to submit an acquisition plan and project execution plan with a projected budget. The approval does not guarantee acceptance of the proposal, but it does allow managers to take the next step toward construction. If it receives final approval from the DOE, the Upgrade would represent an investment of more than $200 million and would bring 40 permanent jobs to the Lab.

"April 19 marks a special day at Jefferson Lab -- for all of those within the Lab, among our scientists, at our universities and in our state and local community, who have worked so diligently toward this point," JLab Director Christoph Leemann said. "I am confident that with the 12 GeV Upgrade, this facility will continue to produce ever more fascinating science."

Relevant Links:

• 12GeV information
• 20 Year Plan

Relevant Images:

• Hall D Schematic
• Diagram of Proposed 12GeV Upgrade
• Photographs of the Announcement
• Front Page Image