Higgs boson key to mass in Universe

The main ring of the Tevatron accelerator at the Fermi National Accelerator Laboratory. After 40 years, more evidence is being reported Wednesday that the end of the biggest manhunt in the history of physics might finally be in sight. Physicists from the Fermi National Accelerator Laboratory in Batavia, Ill., say they have found a bump in their data that might be the long-sought Higgs boson, a hypothesized particle that is responsible for endowing other elementary particles with mass.
The signal, in data collected over the last several years at Fermilab’s Tevatron accelerator, agrees roughly with results announced last December from two independent experimental groups working at the Large Hadron Collider at CERN, the European Organization for Nuclear Research, outside Geneva.
 “Based on the current Tevatron data and results compiled through December 2011 by other experiments, this is the strongest hint of the existence of a Higgs boson,” said the report, which will be presented on Wednesday by Wade Fisher of Michigan State University to a physics conference in La Thuile, Italy.
None of these results, either singly or collectively, are strong enough for scientists to claim victory. But the recent run of reports has encouraged them to think that the elusive particle, which is the key to mass and diversity in the universe, is within sight, perhaps as soon as this summer.
Beate Heinemann, a professor at the University of California, Berkeley, who has been deeply involved in analyzing data from the Large Hadron Collider, said recently of the CERN results, “This very much smells like the Higgs boson.” But, she noted, the signal could also go away when more data is obtained.
The Higgs boson is the key piece of the Standard Model, an ambitious suite of equations that has ruled the universe of high-energy physics for the last few decades, explaining how three of the four fundamental forces of nature work. But the boson itself has never been observed. The theory describes how it should work and behave but does not predict one of its key attributes, namely its mass.
 Last December, two groups, which run giant particle detectors named Atlas and C.M.S. from the CERN collider, reported that they had found promising bumps in their data at masses of 124 billion electron volts and 126 billion electron volts, respectively, those being the units of mass or energy preferred by particle physicists. (By comparison, a proton is about a billion electron volts, and an electron is about half a million.)
 The Fermilab physicists have found a broad hump in their data in the same region, between 115 billion and 135 billion electron volts. Those results came from combining the data from two detectors operated on the Tevatron: the Collider Detector at Fermilab, and DZero. The chances of this signal being the result of a random fluctuation in the data were only about 1 in 100, the group said.
 Dmitri Denisov, a leader of the Fermilab effort, wrote in an e-mail on the way to La Thuile, “It is clearly not the answer to crossword, but an important piece of the puzzle!”
 Rumors of sightings of the Higgs boson have come and gone at both CERN and Fermilab in the last few years, but invariably where one group saw a bump, another saw a dip in the data, and with more data the bumps went away.
This is the first time in the long search for the particle that different groups, indeed different colliders, are in vague agreement.
 It has led to a joke in physics circles now: The Higgs boson has not been discovered yet, but its mass is 125 billion electron volts.
 The Atlas and C.M.S. groups will be trying to combine and reconcile their data in the coming weeks. The Hadron collider, now on winter break, will start up again in April, with protons colliding at four trillion electron volts apiece. CERN has said that the collider will gather enough data this year either to confirm the existence of the Higgs boson or to rule it out forever.
Either outcome, physicists say, will be exciting. If the Higgs does not exist, they will have to come up with a new model of how the universe works. If they do find the Higgs, studying it might give them clues to deeper mysteries the Standard Model does not solve.
 The Tevatron, which was the most powerful accelerator in the world for 20 years, shut down last September.