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'Tantalising, but not yet conclusive': physicists may have glimpsed mystery particle

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An event with four identified muons from a proton-proton collision in ATLAS. This event is consistent with coming from two Z particles decaying: both Z particles decay to two muons each. Such events are produced by Standard Model processes without Higgs particles. They are also a possible signature for Higgs particle production, but many events must be analysed together in order to tell if there is a Higgs signal. This view is a zoom into the central part of the detector. The four muons are picked out as red tracks. Other tracks and deposits of energy in the calorimeters are shown in yellow. Image copyright: CERN An event with four identified muons from a proton-proton collision in ATLAS. This event is consistent with coming from two Z particles decaying: both Z particles decay to two muons each. Such events are produced by Standard Model processes without Higgs particles. They are also a possible signature for Higgs particle production, but many events must be analysed together in order to tell if there is a Higgs signal. This view is a zoom into the central part of the detector. The four muons are picked out as red tracks. Other tracks and deposits of energy in the calorimeters are shown in yellow. Image copyright: CERN

Physicists working on a landmark experiment to understand the building blocks of the universe have announced fresh results in their quest to discover whether the elusive Higgs boson truly exists or not.

Lancaster physicists working on the ATLAS experiment at the Large Hadron Collider at CERN, Geneva, have been sharing results with another team from the sister experiment, CMS, which may indicate they have both found traces of the Higgs boson.

The Higgs boson is key to the astonishing success of the current model in particle physics, because, according to existing theory, it is the mechanism by which particles acquire mass. But the particle has not yet been observed in experiments.

Two separate LHC experiments - Atlas and CMS - have been conducting independent searches for the Higgs and today both groups announced they have made interesting parallel discoveries.

At a seminar at CERN, the heads of Atlas and CMS said they had observed signals in their data at roughly the same mass: 124-125 gigaelectronvolts (GeV). These signals could perhaps be the first evidence of the Higgs.

Dr Harald Fox at Lancaster University is looking for the decay of the Higgs into so-called tau leptons.

He said: "If we are really seeing the Higgs, more work and data will be needed to confirm the signal is genuine. Beyond that, it must also show the correct Higgs behaviour, in particular that it decays into the expected particle types at the expected rates. - for instance, into the tau."

Professor Roger Jones, Head of the ATLAS group at Lancaster University, said: "We cannot say for sure whether the Higgs exists at this point in time. However, the issue will be settled next year, probably by the summer. In some ways, not finding it would be more exciting, as it means so much of what we believe to be true will need to be revised."

Tue 13 December 2011

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