One step closer in the search for the Higgs boson

University of Sydney scientists working with an international team using the Large Hadron Collider at CERN in Geneva, Switzerland, have made an important step towards the discovery of the Higgs boson - a theoretical particle that physicists predict will explain why matter has mass.

Known as the ’God particle’, the Higgs boson has captured the imagination of both the public, and the physicists searching for evidence of the proposed particle.

Associate Professor Kevin Varvell, from the School of Physics and Director of the Sydney node of the ARC Centre of Excellence for Particle Physics at the Terascale , is involved with one of the two giant detectors on the Large Hadron Collider, both of which reported updated results on the search for the Higgs boson at research seminars at CERN this week. The Large Hadron Collider is the world’s largest particle accelerator and started operating in 2008, colliding particles together to investigate a number of big questions in physics.

"Our group here at the University of Sydney works on the ATLAS experiment at the Large Hadron Collider, so we collect and analyse data from ATLAS just like the other several thousand physicists working on the experiment," said Associate Professor Varvell.

"The results presented in Geneva last night were from both the ATLAS and CMS experiments and show that we’re getting closer in our search for the Higgs boson."

"Between the two sets of data, we’ve been able to close the mass range of the predicted Higgs boson, so we’re getting closer to working out its mass if it exists," explained Associate Professor Varvell.

The results are not enough to make any conclusive statement on the existence or non-existence of the Higgs boson, but are a significant step forward in the search for the elusive particle.

"Higgs bosons are predicted to be very short lived and able to decay in many different ways. So with the ATLAS detector, we observe the particles they are predicted to decay into, rather than the Higgs bosons themselves," said Associate Professor Varvell.

"By looking at these decay particles using both the ATLAS and CMS detectors, the teams have found that they can now isolate a more precise mass range that we expect the Higgs boson to be in."

Tantalising hints have been seen in the ranges 116-130 GeV by the ATLAS experiment and 115-127 GeV by CMS, but these are not yet strong enough to claim a discovery of the Higgs boson.

"The results announced last night have the scientific community anticipating that the long search for the Higgs boson may soon bear fruit - by either seeing it emerge with more data in 2012 or by closing the window on its existence as predicted by our current standard theory," said Associate Professor Varvell.

"Next year will be a really significant time in the search for the Higgs boson - we should have more refined analyses from both ATLAS and CMS which will give us a more definitive answer."

The Higgs boson is named after British physicist Peter Higgs, who postulated in 1964 that a field in some respects similar to an electromagnetic field might be what gives particles their mass. In this scenario, particles acquire mass by interacting with the Higgs field, and directly observing the related Higgs boson particle in experiments would be the evidence that the Higgs field exists.
"Our group is doing work on the ATLAS program that includes searching for evidence of supersymmetry, which would require that there are at least five different types of Higgs boson, if that theory is correct. We’re also using ATLAS to look for other new and exotic things."

The ATLAS experiment involves around 3000 scientists from 37 countries and both ATLAS and CMS are general-purpose detectors used at the Large Hadron Collider.

"Whichever way the search for the Higgs boson goes, it will be a big step towards a deeper understanding of the workings of the Universe at a fundamental level."