Physicists on both sides of the Atlantic on Monday claimed major new progress in the search for the elusive Higgs boson, the so-called God particle that is the cornerstone of the standard model of particles and forces.
Two teams of researchers using the Tevatron accelerator at the Fermi National Accelerator Laboratory in Batavia, Ill., said they have eliminated about a quarter of the potential mass range for the Higgs boson suggested by earlier experiments, narrowing the search to a more manageable region. They also said their research hints that the Higgs could lie at the lower end of the mass range, which would make it possible to find it using the Tevatron.
Meanwhile, researchers at the Large Hadron Collider under the Swiss-French border — which was built in large part to find a Higgs boson — said that the accelerator is exceeding expectations and that it has, in only three months, "rediscovered" a whole family of particles that it took smaller American accelerators years to identify.
The team also said that it has identified for the first time in Europe the short-lived top quark, which has been seen only by accelerators in the United States.
"From now on, we are in new territory," said physicist Oliver Buchmueller, a senior researcher at the European Organization for Nuclear Research, or CERN, which operates the Large Hadron Collider.
Both reports were presented in Paris at an international high-energy physics conference.
Existence of the Higgs boson was postulated in 1964 by British theoretical physicist Peter Higgs as an explanation for why some elementary particles have mass and others do not. Despite extensive efforts at locating it, it is the only particle from the standard model that has not yet been identified.
If researchers can find it, they will develop a new understanding of the primal forces of nature. If it cannot be found, however, new theories may replace the standard model, which underlies most current research in particle physics.
Previous experiments had indicated that the Higgs boson, if it does exist, must have a mass of 114 billion to 185 billion electron volts (114 to 185 GeV). The mass of a proton is about 1 GeV.
After sifting through more than 500 trillion proton-antiproton collisions produced in the Fermilab Tevatron, physicists have been able to rule out with 95% confidence masses between 158 and 175 GeV, about a quarter of the predicted range.
"That leaves a little room on the high side, but it now looks more and more likely that it is going to be in the low part of the range," said physicist Giovanni Punzi, a spokesman for the project. "That's interesting in general, but it is interesting for us because that's the place where we have the best sensitivity in the Tevatron. That means it's even more likely than we thought that we could find it."
The Tevatron experiment searching for the Higgs was originally scheduled to stop running by the end of 2011. "The recent successes are encouraging us to try to have three more years of running to get more data," Punzi said. "We definitely feel encouraged to try and go [longer] and find out everything we want to find out."
Meanwhile, the LHC — whose operation was delayed for 14 months by engineering problems — is now operating at energy levels of 7 trillion electron volts (7 TeV), more than three times the level reached by any previous accelerator. Administrators plan to have the $10-billion device colliding protons at 14 TeV by the end of 2011.
"Whether the LHC will [discover the Higgs] by 2012, I don't know," Rolf Heuer, director-general of CERN, said at the meeting. "I hope it might happen, but if it doesn't happen then it might be three or four years later."
If either team finds the Higgs, experts said at the meeting, it may be necessary to build a new accelerator to explore its properties. The LHC, with its 17-mile circumference, is great for colliding protons. But when it is used for smaller elementary particles, such as the electron, much of the energy fed into the system is bled off by a process known as synchrotron radiation. Eliminating that requires straight-line acceleration, available at the Stanford Linear Accelerator.
Physicists are thus proposing the construction of a 19-mile-long linear accelerator (the Stanford device is only 2 miles long) to explore the properties of the Higgs. Such a device could reach energies of 500 GeV, compared with 50 GeV at Stanford. Where the device, tentatively named the International Linear Accelerator, would be located, however, depends on which country would be willing to put up the bulk of the $10 billion necessary for its construction.