Physicists hot on the trail of a long-sought fundamental particle are being given extra time to flush out their quarry--but not much of it. Earlier today, Luciano Maiani, the director-general of CERN, the European Laboratory for Particle Physics, announced that experiments to find evidence for a Higgs boson will be prolonged on the world's largest particle accelerator until 2 November. CERN's Large Electron-Positron Collider (LEP) was supposed to be shut down at the beginning of October.
After 10 years of banging electrons and positrons together at higher energies than any other machine in the world, the time has come to dismantle LEP and install a new machine. But in August, scientists working on one of LEP's four detectors saw exciting signs of Higgs bosons, followed by more hints on another detector earlier this month. This theoretical particle is the crucial missing component in the physicists' "Standard Model," an assemblage of theories that accounts for almost everything observed so far in the subatomic realm. Precise measurements of its properties would provide insights into the nature of physical processes beyond that model, such as those that would produce new "supersymmetric" particles.
It may seem odd--even perverse--that LEP has waited until the very end of its life to produce Higgs particles, but there's a simple reason. So as not to burn out their machine prematurely, LEP's operators always kept something in reserve. For the past month, though, such caution has been discarded and LEP's operators have been running their beams at 103 giga-electron volts (GeV). At the lower beam energies used previously, there's not enough energy for a colliding particle pair to make a 114-GeV Higgs and a 91-GeV Z, which is what seems to be going on. With a total of 206 GeV, there is.
The extra month of research--any longer would have set back construction of the Large Hadron Collider (LHC)--will double the amount of data taken at this highest energy. That's not enough to settle things for sure, but it might add more hints of a 114-GeV Higgs. According to John Ellis in CERN's theory division, these might include a telltale four-jet event appearing in another detector or an event that looks like a Higgs decaying into two leptons instead of two jets. "What you are looking at is not a paper saying 'Discovery [of a Higgs],' " says Ellis. "But if the effect is repeated you might get a paper saying 'Evidence ...,' while at the moment all you could get would be a paper saying 'Indications ...'"
The likelihood now is that the "Discovery" paper will come not from CERN but from Fermilab in the United States, where the new improved Tevatron--which will begin producing data next year--may well be able to find conclusive evidence of a 114-GeV Higgs, if one exists. But that would still leave CERN with a lot to look forward to. As Ellis points out, a Higgs at 114 GeV would effectively guarantee that the Standard Model will break down at LHC's higher energies, and thus the new machine will be guaranteed uncharted realms of discovery from day one--with no pesky time limits.