No Sighting of Higgs, But Fermilab Physicists Say They May Be Close

26 July 2010 10:40 am


Getting close. Physicists working with Fermilab’s CDF and D0 particle detectors have ruled out the existence of the Higgs boson in a wider range of masses, which gives them hope that they may be on the verge of spotting the elusive particle.

PARIS—A week ago, a rumor sped across the Internet that physicists at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, had discovered a particle called the Higgs boson, the most-coveted prize in high-energy physics and the fundamental particle thought to give all others their mass. In fact, researchers working with Fermilab's aging atom smasher, the Tevatron, have not spotted the Higgs. But they have narrowed the range of masses in which the particle most likely exists, they reported here today at the International Conference on High Energy Physics.

That improved nonobservation has Fermilab physicists convinced that they have a real shot at seeing the Higgs before it's bagged by a more-powerful atom smasher, Europe's Large Hadron Collider (LHC). So they're pushing to run the Tevatron for three extra years, through 2014. "There's definitely a window of opportunity here," says Dmitri Denisov, a physicist at Fermilab and co-spokesperson for the 500-member team working with the massive D0 particle detector, part of the lab's Higgs-hunting effort.

But Fermilab officials aren't automatically supporting the plan, especially as the lab is building a new $260 million neutrino experiment called NOvA that will be its main facility once the Tevatron shuts down. "Things are really ramping up on NOvA, and we don't want to hammer on that," says Young-Kee Kim, Fermilab's deputy director. Still, lab leaders take seriously the proposal to extend the Tevatron, she says.

Higgs bosons are thought to lurk "virtually" in the vacuum of empty space and drag on other particles to give them inertia, or mass. But physicists' standard model of the fundamental particle does not predict how much the Higgs itself will weigh. So scientists must go searching for it. Previous experiments show that it probably has a mass between 114 and 185 giga-electron volts (GeV), or 121 and 197 times the mass of the proton. Last year, experimenters working with D0 and the Tevatron's other particle detector, CDF, took a chunk out of that possible range, reporting that the Higgs most likely does not weigh between 162 GeV and 166 GeV. Now, they've widened that "exclusion window" to between 158 GeV and 175 GeV.

That result suggests that the Tevatron teams have nearly enough data and sensitivity to spot the Higgs if it exists anywhere in the entire 114-to-185-GeV range. "Everywhere we are very, very close," Denisov says. If the Tevatron keeps smashing protons into antiprotons through 2014, then researchers at Fermilab should gather about 65% more data than they'll have by the end of next year. That ought to be just enough to glimpse the Higgs—if it's there—before physicists at the European particle physics laboratory, CERN, near Geneva, Switzerland, can nab it with the LHC, which has been taking data only since March. "It's really a matter of who can get it done first," says Rob Roser, a Fermilab physicist and co-spokesperson for the 600-member team working with Fermilab's CDF particle detector.

Fermilab physicists have a crack at the prize only because the LHC will shut down for more than a year at the end of 2011. That break will give workers a chance to repair thousands of unreliable solder connections between the LHC's massive superconducting magnets. In September 2008, just days after it first started up, the LHC suffered a catastrophic breakdown when one of those connections melted. After 14 months of repairs, CERN officials decided to run the LHC at no more than half energy—which is still 3.5 times the Tevatron's energy—until all of the questionable splices could be resoldered. That shutdown will stretch for 15 months to provide time for an unrelated modification that should enable the LHC to smash particles at a greater rate, Stephen Myers, CERN's director of accelerators and technology, said at the meeting.

Some European physicists seem more sanguine about the idea of running the Tevatron through 2014 than their American colleagues. "In an ideal world, I think it would be good to have the Tevatron running in parallel with the LHC," says Guido Tonelli of the University of Pisa in Italy, who is spokesperson for the 3800-member team working on the colossal CMS particle detector at CERN. "For the next 2 or 3 years, the two machines will be complementary." But Melvyn Shochet, a physicist at the University of Chicago in Illinois and chair of the U.S. government's High Energy Physics Advisory Panel, notes that Fermilab officials live very much in a world of finite resources. "I don't see anybody coming along with a check for the $100 million or whatever it costs to run the Tevatron for 3 years," he says. "So Fermilab has to consider what it's going to give up" to run the Tevatron. Look for a decision in the next few months.

*This story has been corrected. The original version implied that CERN officials had set the length of the shutdown at 12 months, instead of 15 months.

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