As we patiently await the announcement from CERN physicists as to whether or not the Higgs boson has finally, irrefutably been discovered by the Large Hadron Collider (LHC), physicists of the (now-retired) Tevatron particle accelerator at Fermilab, Ill., had an announcement of their own yesterday.
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“The Tevatron experiments accomplished the goals that we had set with this data sample,” said Fermilab’s Rob Roser, spokesperson for the CDF experiment at Fermilab. “Our data strongly point toward the existence of the Higgs boson, but it will take results from the experiments at the Large Hadron Collider in Europe to establish a discovery.”
Key to the Fermilab announcement is the dataset depicted in the graph above. After 500 trillion particle collisions recorded inside the Tevatron detectors since 2001, U.S. physicists may have spotted a “bump” in their data (red circle). This bump corresponds to an “excess” of decay particles that may reveal a Higgs boson at an energy from 115 to 135 GeV/c2
“The Tevatron results indicate that the Higgs particle, if it exists, has a mass between 115 and 135 GeV/c2, or about 130 times the mass of the proton,” says the Fermilab press release.
But like all hints of a Higgs discovery, scientists of the Tevatron’s CDF and DZero collaborations can’t point at the bump in the data and announce to the world that they’ve discovered the Higgs.
Although the signal looks real, the combined CDF and DZero result has a statistical significance of 2.9 sigma. “This means there is only a 1-in-550 chance that the signal is due to a statistical fluctuation,” says Fermilab. Even so, that’s a long way off the desired “Gold Standard” of a 5-sigma result that physicists need before a discovery can be announced.
So, all eyes are now on the LHC. “It is a real cliffhanger,” said DZero co-spokesperson Gregorio Bernardi.
Interestingly, the Tevatron hunt for the Higgs focuses on a different kind of Higgs particle decay, one that the LHC is not sensitive to.
“Just as a vending machine might return the same amount of change using different combinations of coins, the Higgs can decay into different combinations of particles. At the LHC, the experiments can most easily observe the existence of a Higgs particle by searching for its decay into two energetic photons. At the Tevatron, experiments most easily see the decay of a Higgs particle into a pair of bottom quarks.” — Fermilab.
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“We know exactly what signal we are looking for in our data, and we see strong indications of the production and decay of Higgs bosons in a crucial decay mode with a pair of bottom quarks, which is difficult to observe at the LHC. We are very excited about it,” said Bernardi.
“We achieved a critical step in the search for the Higgs boson,” added Dmitri Denisov, DZero co-spokesperson. “While 5-sigma significance is required for a discovery, it seems unlikely that the Tevatron collisions mimicked a Higgs signal. Nobody expected the Tevatron to get this far when it was built in the 1980s.”