Tantalising hints of the Higgs boson will be confirmed or ruled out at the LHC in the coming months, say researchers
by Ιan Sample
Physicists at the Large Hadron Collider near Geneva are edging ever closer to answering one of the most profound questions in particle physics: does the Higgs boson exist?
Speaking at a conference in Paris on Friday, researchers said they had narrowed down their search for the particle, leaving only a small range of masses that the elusive Higgs might have.
The latest results contain some hints that the particle might lurk in the lighter range of masses, but further work over the coming months is needed to confirm or rule out these weak signals.
The Large Hadron Collider smashes protons together at close to the speed of light to recreate in microcosm the energetic conditions that existed a fraction of a second after the big bang.
These microscopic fireballs of energy condense into well known subatomic particles, but scientists hope that among them they will see other more exotic particles, including the Higgs boson.
The Higgs accompanies a theory put forward in 1964 by six physicists, including Peter Higgs at Edinburgh University. The theory describes an invisible field that pervades all of space and endows fundamental particles with mass.
Without the field, or something to do its job, elementary particles would weigh nothing and forever zip around at the speed of light.
Speaking at the Hadron Collider Physics meeting in Paris, teams working on the LHC’s two multipurpose detectors, Atlas and CMS, said they had combined the results each had gathered until August this year.
The experiments together rule out the simplest version of the Higgs boson over a mass range from 141GeV (gigaelectronvolts, the units of mass used in particle physics) to 476GeV. One GeV is roughly equivalent to the mass of a proton, a subatomic particle found in atomic nuclei.
The vast and complex job of combining the data collected by both detectors is a feat in itself and prepares the ground for physicists to combine the whole year’s results over the next few months.
“As soon as we have digested the full 2011 statistics, the combination can be redone,” said Guido Tonelli, spokesman for the CMS collaboration.
A predecessor to the LHC, a machine called the Large Electron Positron collider at Cern, the particle physics laboratory near Geneva, ruled out the existence of the Higgs boson up to a mass of 114GeV, but saw what might have been hints of the particle before it shut down in 2000 to make way for the LHC.
That leaves a mass range of 114GeV to 141GeV where the Higgs particle might still be found. Tonelli said both CMS and Altas have small signals in the region, but nothing conclusive. The signals are referred to as “excess events”, which might be the caused by the Higgs boson decaying into other, more familiar particles.
“There’s a broad excess under 140GeV and in that range there are three regions in which the excess looks a little more pronounced. Some or all of these fluctuations might disappear or we might see one of them strengthen with the full statistics,” Tonelli said.
“Whether it will be strong enough to reach a conclusion, we have to wait. The fact that we continue to see this excess even in the new data hints that something is happening there,” he added.
In September, managers at Cern commissioned a report from its scientific policy committee on the implications of failing to find the Higgs boson between 114GeV and 600GeV and how to communicate such an eventuality to the public. The report suggests that “finding the Higgs boson, exactly as postulated in the Standard Model, would be a triumph. Ruling it out would be revolutionary, requiring textbooks to be rewritten.”