Exploring the Nature of Matter
November 3, 2008
If you look at the header on a letter sent by any of us at Jefferson Laboratory, you will find the words, “ Exploring the nature of matter.” And you might ask, what do they mean?
At Jefferson Laboratory, we scatter electrons like Hofstadter did in the '50s when he explored nuclei. That’s why one of our roads is named for him. The scattering process is described as the exchange of a virtual photon between the electrons and the charged constituents in the nucleus. For instance, when we see a flash of light, it means an electron in our eye has received a photon emitted by another charged particle. So scattering electrons is a process that, almost literally, allows us to see inside the target. This process was used circa 1970 by Friedman, Kendall and Taylor and collaborators, in their Nobel Prize-winning experiments, to observe the constituents, the quarks, inside nucleons.
In experiments at Jefferson Lab, with the use of high-intensity beam and spin (of the beam, of the target and of the final state particles) we do experiments that are sensitive to many properties of the structure of the nucleus and the nucleon. Our current experimental program is carried out using electrons with up to 6 giga-electron volts (GeV) of energy. These are produced by a superconducting continuous wave accelerator. In many ways, the accelerator is a precursor to a number of modern machines that use superconducting radio frequency acceleration. A non-exhaustive list could include the Spallation Neutron Source at Oak Ridge, the XFEL machine at DESY, Hamburg, the Facility for Rare Ion Beams and Project X in the United States and perhaps in the future, the International Linear Collider. They enable exploration of matter using many different techniques.
The success of our current 6 GeV program and its potential has led to approval of the 12 GeV Upgrade, a project that will cost about three times the annual operations budget of the laboratory and will open another decade or more of forefront research. The research and development for the upgrade is done, and we are starting the construction phase in parallel with our ongoing 6 GeV program. The upgrade will bring new dimensions to the physics program. The beautifully conceived polarized photon spectroscopy experiment in the new Hall D may provide us with insight into how the quarks and gluons really interact with each other. We have work to die for.
You could imagine that if electron scattering started in the ‘50s, and generated one Nobel Prize with work in the ‘60s and ‘70s, then perhaps it should die with the rest of us baby boomers. Not so! If you look at the accelerators people in nuclear and particle physics are considering for the future you will find electron-ion colliders figuring strongly.
In the spring of this year, you would have thought there were three machines being considered; an electron beam colliding with the the Large Hadron Collider's proton or heavy ion beam (LHeC), or an electron beam colliding with the Relativistic Heavy Ion Collider's ions (e-RHIC) and a dedicated complex at Jefferson Laboratory with high luminosity and exquisite spin control (ELIC). A couple of weeks ago, I thought there were four options, and since then others have appeared. So, the electron ion collider (EIC) concept, a natural extension of the program at Jefferson Laboratory, is currently hot.
Of course before anyone seriously considers building a machine, we need a strong, well-documented case for the physics, as well as a strong design for the machine and a tractable cost. Jefferson Laboratory physicists are contributing thoughts to the physics, the experiments and the machine designs.
As noted earlier, electron scattering is using virtual photons to look at matter. The superconducting radiofrequency technology enables us to choose different wavelengths and to produce powerful beams of real photons. This is the basis for a second component of our physics and technology. We have developed a high-power Free-Electron Laser that uses Energy Recovering Linac technology. We are eager to expand our modest physics programs in that arena. Perhaps we have in our hands the basis for a future generation of light sources.
There are other things we do, from medical imaging to education, which broaden our impact on society but at root the Jefferson Laboratory motto, “ Exploring the nature of matter,” accurately captures what we, as a laboratory, are about.