Warped Passages - Lisa Randall [90]
By 1994, several of CDF’s working groups had seen events that looked like the top quark (see Figure 54 for an example), but they weren’t really sure. Although CDF couldn’t say with certainty that they found the top quark that year, both D0 and CDF confirmed discovery in 1995. A friend of mine on D0, Darien Wood, described the intensity of the final editorial board meeting at which D0 completed the data analysis and the paper that would report their results. The meeting went through the night and into the next day, with people occasionally napping on table tops.
Figure 54. A top quark event as recorded by D0, which detects the decay products of the top quark and top antiquark that are produced simultaneously. The line in the upper right is a muon, which reaches the outer portion of the detector. The four rectangular-like blocks are four jets that were produced. The line to the right is the missing energy of the neutrino.
D0 and CDF received joint credit for discovering the top quark. A new particle was produced that had never been seen before. This newly discovered particle joined the ranks of other, established Standard Model particles. By now, so many top quarks have been seen that we know the top quark’s mass and its other properties extremely precisely. In the future, we expect higher-energy colliders to produce so many top quarks that there is a danger that the top quarks themselves will become the background that mimics and interferes with the discovery of other particles.
New physics is almost certainly there to be seen. We will soon see why unresolved Standard Model issues are telling us that new particles and physical processes should appear when colliders reach only slightly higher energies than is possible at present. Experiments at the Large Hadron Collider (LHC) will look for evidence of structure beyond the Standard Model. If those experiments are successful, the reward will be fabulous—a better understanding of the underlying structure of all matter. High energy, many-particle collisions, and clever ideas will all contribute to accomplishing this difficult task.
Precision Tests of the Standard Model
We will now briefly move from the plains of Illinois to mountainous Switzerland—the location of CERN, the Conseil Européen pour la Recherche Nucléaire (now called the Organisation Européenne pour la Recherche Nucléaire or, in English, the European Organization for Nuclear Research, though the old acronym, CERN, has stuck). Many experiments have tested the Standard Model’s predictions, but none were as spectacular as those performed between 1989 and 2000 at the Large Electron-Positron collider (LEP) located at the CERN accelerator facility.
The CERN site was chosen for its central location within Europe. CERN’s main entrance is so close to the French border that the guard booth separating the two countries is almost directly outside. Many CERN employees live in France and cross the border twice daily. They are rarely bothered when crossing the border—unless their car isn’t up to Helvetic standards, in which case the Swiss won’t let them in. The only other danger is being an absent-minded professor, as one colleague can attest to. The guards stopped and searched him when he didn’t stop at the border because he was distracted by thoughts about black holes.
The difference between the locations of Fermilab and CERN could not be more striking. CERN is adjacent to the beautiful Jura mountains (see Figure 55) and is only a short drive from Chamonix, a remarkable valley that runs between mountains covered with glaciers that descend practically to the road (though less so with global warming), and lies at