Jefferson Lab in the News
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CLAS Physicists Study 'Nothing'!
New measurements taken using Jefferson Lab's CEBAF Large Acceptance Spectrometer are telling us more about how matter is produced from "nothing," that is, the vacuum. Physicists have long known that matter and anti-matter can be created when energetic particles strike one another. Visualize a bowling ball hitting its rack of 10 pins so hard that the 10 pins turn into 11 normal pins and one "anti-pin." The new particles are not really created from nothing, they are created from the available kinetic energy of the energetic particles that collide. Energy is conserved and so is matter; that's why a new anti-matter particle is created each time a matter particle is created.
Physicists think that the first step in the process is to produce a pair of quarks: one quark and one anti-quark. Like electrons and protons, quarks are also thought to spin on their axis, like little tops; and they were expected to be produced with their spins lined up. However, these CLAS measurements indicate that what happens is just the opposite! They emerge with spins anti-aligned. The experiment was performed in Hall B — one of JLab's three experiment halls — and involved studying how the polarization of a produced Lambda particle was correlated with the electron beam's polarization. The results have been published in Physical Review Letters.
Although seemingly esoteric, these results show that we still do not understand the basic structure of the vacuum that well. One hundred years ago the vacuum was thought to consist of an "ether" through which light propagated as waves. Albert Michelson, Edward Morley, Albert Einstein and others disproved this hypothesis and the vacuum became an empty void. Twentieth century quantum field theories have now filled this once-empty space with virtual particles. It's now obvious that a vacuum is not the cold, empty place it was once thought to be! JLab physicists are studying the spin of the produced quarks in hopes of understanding the vacuum better as well as the matter that populates it.
Jefferson Lab is a Department of Energy Office of Science basic physics research facility located in Newport News, Va.
Graphics as they appear in the June 2003 CERN Courier (produced by Mary Beth Stewart, JLAB)
Related article:
JLab results put new spin on the vacuum