Warped Passages - Lisa Randall [91]
Figure 55. The CERN site with the Alps in the background. The Large Hadron Collider ring, in which two beams of protons will circulate underground, is indicated.
CERN was created after World War II, in the nascent atmosphere of international collaboration. The original twelve member states were West Germany, Belgium, Denmark, France, Greece, Italy, Norway, the Netherlands, the United Kingdom, Sweden, Switzerland, and Yugoslavia (which left in 1961). Subsequently, Austria, Spain, Portugal, Finland, Poland, Hungary, the Czech and Slovak Republics, and Bulgaria have joined. Observer states involved in CERN activities include India, Israel, Japan, the Russian Federation, Turkey, and the United States. CERN is truly an international enterprise.
CERN, like the Tevatron, has many accomplishments to its credit. Carlo Rubbia and Simon van der Meer were awarded the 1984 Nobel Prize for Physics for designing the original CERN collider and discovering the weak gauge bosons, a success story that destroyed America’s monopoly on particle discoveries. CERN was also where an employee, the Englishman Tim Berners-Lee, came up with the World Wide Web, HTML (hypertext markup language), and http (hypertext transfer protocol). He developed the Web so that many experimenters in scattered nations could be instantaneously linked to information and so that data could be shared among many computers. Of course, the repercussions of the Web have been felt far beyond CERN—it’s often difficult to foresee the practical applications of scientific research.
In a few years, CERN will be the nexus of some of the most exciting physics results. The Large Hadron Collider, which will be able to reach seven times the present energy of the Tevatron, will be located there, and any discoveries made at the LHC will almost inevitably be something qualitatively new. Experiments at the LHC will seek—and very likely find—the as yet unknown physics that underlies the Standard Model, confirming or rejecting models such as the ones I describe in this book. Although the collider is in Switzerland, the LHC will truly be an international effort; experiments for the LHC are currently being developed all over the globe.
But back in the 1990s, physicists and engineers built the unbelievable LEP (Large Electron-Positron collider) at CERN, a Z boson “factory” that churned out millions of Zs. The Z gauge boson is one of the three gauge bosons that communicate the weak force. By studying millions of Zs, experimenters at LEP (and also at SLAC, the Stanford Linear Accelerator Center in Palo Alto, California) could do detailed measurements of the Z boson’s properties, testing the predictions of the Standard Model to an unprecedented level of precision. It would take us too far off track to describe each of these measurements in detail, but in a moment I’ll give you an idea of the stunning precision that was achieved.
The basic premise behind the Standard Model tests was very simple. The Standard Model makes predictions for the masses of the weak gauge bosons and the decays and interactions of the fundamental particles. We can test the consistency of the theory of weak interactions by checking whether the relationships among all these many quantities fit the theory’s predictions. If there were a new theory with new particles and new interactions that became important at energies near the weak scale, there would be new ingredients that could change the weak interaction predictions from their Standard Model values.
Models that go beyond the Standard Model therefore make slightly different predictions for the Z boson’s properties than those predicted by the Standard Model itself. In the early 1990s everyone used an incredibly cumbersome method for predicting the Z’s properties in these alternative models so that the predictions could