Unusual data bumps detected by two teams at Large Hadron Collider thought to be glimpse of elusive source of particle mass
Scientists may have caught their first glimpse of the elusiveHiggs boson, or “God particle”, which is thought to give mass to the basic building blocks of nature.
Researchers at the Large Hadron Collider at Cern, the European particle physics lab near Geneva, announced the findings at a conference on Friday yesterday.
The world’s most powerful atom smasher hunts for signs of new physics by slamming subatomic particles together at nearly the speed of light in an 18-mile round tunnel beneath the French-Swiss border.
Speaking at the meeting, teams working on two of the collider’s huge detectors, Atlas and CMS, independently reported unusual bumps in their data that could be the first hints of the particle.
Physicists stressed that it was too early to know whether the signals were due to the missing particle.
Bumps that look like new discoveries can be caused by statistical fluctuations in data, flaws in computer models and other glitches, they said.
“We cannot say anything today, but clearly it’s intriguing,” Fabiola Gianotti, spokeswoman for the 3,000-strong Atlas team, said. She said the picture would become clearer as the groups gathered more data and combined results in the next few months. The view was shared by Guido Tonelli, spokesman for the CMS group, said more data was needed to understand whether the bumps were due to “statistical fluctuations or possible hints of a signal”.
The long-sought particle was first postulated in 1964 by Peter Higgs, a physicist at Edinburgh University, in a theory that described how fundamental particles gained mass from an invisible field that pervaded the cosmos.
The field has been compared to a snowfield that clings to particles and slows them down to different extents. Light particles pass through the field swiftly as if they have skis on, while heavy particles trudge through as though walking barefoot.
The boson was nicknamed the “God particle” in 1993 by the Nobel prize-winning physicist, Leon Lederman. The monicker is detested by Higgs. “I find it embarrassing because, though I’m not a believer myself, I think it is the kind of misuse of terminology which I think might offend some people,” he said.
From previous work, the Higgs boson was thought to have a mass somewhere between 114 and 185GeV (gigaelectronvolts) – one GeV is roughly equivalent to the mass of a proton, a subatomic particle found in atomic nuclei.
The Atlas team reported a Higgs-like bump in their data between 120 and 140GeV. In a later session, the CMS group announced two bumps in the same region.
Matt Strassler, a theoretical physicist at Rutgers University in New Jersey, commented on his blog: “Exciting … but far too early to be sure this is anything interesting.” He added: “This is certainly something we’ll be watching.”
Surprise LHC blip hints at Higgs – again
Particle watchers could be forgiven for feeling a little weary. An unexpected blip in the data glimpsed at the Large Hadron Collider is once again being attributed to the Higgs boson – the hypothetical particle thought to endow all others with mass.
The news raises hopes that the long-anticipated particle might finally be within reach – and is on somewhat firmer ground than a tantalising report earlier this year that turned out to be a false alarm. However, the blip – an excess of particles of a certain energy – is not yet big enough to rule out a statistical fluke that might vanish when more data is gathered.
In the wreckage of colliding protons, the ATLAS detector at the LHC, located near Geneva, Switzerland, has found an unexpected abundance of pairs of W bosons, which carry the weak nuclear force, with energies between about 120 to 140 gigaelectronvolts (GeV).
That could be due to a Higgs particle with a mass in that range decaying into pairs of W bosons (particle masses and energy are treated interchangeably because mass is readily converted into energy in particle collisions and decays).
The team also saw smaller excesses in pairs of photons and Z bosons, which carry the weak nuclear force and could be due to Higgs’ decays too.
The combined statistical significance, taking all three types of excess reported by ATLAS into account, is 2.8 sigma, slightly below the 3 sigma threshold (equivalent to a 1-in-370 chance of being due to a fluke) that a measurement must pass to count as “evidence” for something new: only 5 sigma data, equivalent to a 1-in-1.7 million chance of being due to a fluke, gains “discovery” status.
The other main detector at the LHC, called CMS, has found an excess in a similar range, between 130 and 150 GeV, reports Nature. The size of that excess is roughly 2 sigma, writes physicist Adam Falkowski on the Resonaances blog.
If all this sounds a tad familiar, rewind back to April, when four physicistsclaimed to have found hints of the Higgs in ATLAS data in a study abstract leaked online. A subsequent official analysis by the collaboration of 700 physicists who run ATLAS concluded (pdf) that result was an error. Unlike that claim, the new excesses have been vetted by the ATLAS and CMS collaborations respectively.
And what of the Tevatron accelerator in Batavia, Illinois, which has beenlocked in a race with the LHC to be the first to spot the Higgs? The Tevatron has not yet found evidence for the Higgs and is set to shut down at the end of September, but there is still time for it to weigh in on this with the data it is still collecting. Exciting times ahead, but expect more fits and starts.