NOT THE LIGHT OF DISCOVERY: Technicians in 1999 worked on one of the 3,368 electromagnets in LEP¿s 27-kilometer-long tunnel. Last November crews began dismantling LEP, despite hints that another major discovery may have been imminent. Image:
In a move that surprised and dismayed many physicists, one of the world's leading laboratories has chosen not to continue an experiment that showed every sign of being on the verge of discovering an elusive particle that would have placed the capstone on a century of particle physics. The experiment was the last gasp of the venerable Large Electron-Positron collider (LEP), located near Geneva, Switzerland, and part of the European laboratory for particle physics (CERN). The particle was the long-sought Higgs, which is profoundly unlike any other particle discovered in human history and is the final jigsaw piece needed to complete the Standard Model of particle physics. The decision came down to the judgment of one man, Luciano Maiani, CERN's director general, who chose to shut down LEP on schedule to avoid delaying construction of CERN's next big experiment, the Large Hadron Collider (LHC), which is slated to be turned on in 2005.
Postulated independently by British physicist Peter Higgs and others in 1964, the Higgs plays a unique role in particle physics. In one guise, the Higgs is a field permeating the universe and giving the other particles their mass. If the field were turned off, the particles making up your body would presumably fly apart at the speed of light like so many photons. We have no way of directly detecting the all-pervasive Higgs field, but its other guise--individual Higgs particles, like tiny concentrated knots in the field--should be producible in violent collisions at accelerators. By studying the particle, physicists can verify the theory and pin down the Higgs's many unknown properties.
In 2000 researchers optimized the 11-year-old LEP to conduct one last search for the Higgs, pushing it to achieve collision energies of 206.5 billion electron volts (GeV)--about 14 GeV beyond its original design parameters. Most likely the Higgs would be too massive to fall within LEP's extended reach, but in the summer, physicists saw signs of Higgs particles. Out of millions of collisions, nine produced Higgs candidates. A one-month extension to LEP yielded additional results, sufficient to conclude that the odds that the results were noise were one in 250--a tantalizing result but much too uncertain to proclaim "discovery." The data indicated that the Higgs has a mass of about 115 GeV (the remaining collision energy goes into creating a so-called Z particle at 91 GeV). By comparison, a proton is 1 GeV. A 115-GeV Higgs would agree nicely with predictions of supersymmetry models--the idea that particles in the Standard Model have "supersymmetric" partners.
This article was originally published with the title Higgs Won't Fly.