The Higgs discovery was at the very edge of what had been predicted; so it is either the last proof of the old Standard Model of physics, or the first hint that something very strange lies beyond it

PHYSICISTS ARE STUCK. The Higgs discovery has been dubbed ‘science’s great leap forward’ by the media, but physicists fear it could actually be “a little bit boring”.

Or it could be the dawn of completely new physics that will revolutionise everything.

They just don’t know which.

The discovery, announced to breathless crowds of scientists and media in Geneva and in Melbourne, where the 36th International Conference on High Energy Physics is being held, ricocheted around the world on Wednesday, dominating Twitter hashtags for hours and headlining more than 5,000 news websites.

The universe’s DNA

Likened by The Economist as important as the discovery of DNA, the Higgs find, made by teams of scientists at the Large Hadron Collider (LHC) near Geneva, had been highly anticipated.

“It’s the biggest announcement in particle physics for about 10 years,” said Ehud Duchovni, from the Weizmann Institute of Science in Israel, during a morning tea break. He was referring to the discovery in 2002 that neutrinos, previously thought to be massless, must have at least a small amount of mass.

“Clearly it’s an exciting result,” said Peter Jenni, the former spokesperson for the ATLAS experiment at the European Organisation for Nuclear Research (CERN), home of the LHC.

“But for the physicists, finding the exact mass of the Higgs boson was a ‘known unknown’.”

It’s time for the unknown unknowns

It was a milestone in particle physics, “and without it, we would never have gotten the money for the experiment,” Jenni said. “But now the real fun starts … now: we have the ‘unknown unknowns’.”

The first of the unknowns is whether or not the particle they’ve found really is the Higgs boson predicted by the Standard Model of physics.

The Standard Model is a complex theoretical matrix that describes all the fundamental particles in the universe, and has accurately predicted all those which have been discovered since the 1970s.

However, the Standard Model doesn’t predict a number of observations in the past few decades that seemingly throw a spanner in the works, including the unexpected absence of antimatter in the universe.

“It’s exciting … but a bit boring”

“If it’s just the Standard Model Higgs that we are finding, it’s exciting … but a little boring,” said Albert de Roeck, from the CMS (Compact Muon Spectrometer) experiment at CERN.

If, however, the particle is not the Higgs boson, the alternative is that it is the first of many Higgs bosons.

“Maybe there is not just one Higgs … maybe there is a multiplicity of Higgs,” said Pier Odonne, director of Fermilab, a U.S. high-energy particle physics lab in Illinois, USA.

There may be as many as 5 Higgs

The Higgs discovery is at the very edge of what had been predicted: hence, it may be the last proof of the old Standard Model, or the very first hint of a whole new, unknown model – and therefore, new physics – was needed.

One popular – but unproven – theory in physics predicts no less than five Higgs bosons: three of them neutral, and two carrying a charge.

The theory, known as supersymmetry, proposes that for every particle, there is a heavier ‘super-partner’ particle.

It had been hoped that the LHC would see traces of these superpartners in the particle collisions. However, there has been no evidence of them to date, and the collider keeps eliminating the possible masses at which they might exist.

Nevertheless, the theory of supersymmetry has remained popular in physics because it is mathematically elegant, tying up a lot of loose ends in equations of physicists.

It also holds the promise of helping to solve many outstanding anomalies, such as dark matter.

“Supersymmetry provides a very good candidate for dark matter particles that maybe have been produced a short time after the Big Bang and have survived until now,” said Jenni.

Supersymmetry: a hope for new physics?

There is a chance that what they’ve discovered at CERN is just one of the Higgs bosons predicted by supersymmetry. If it is, it could open up many new possibilities for the future of physics research.

Right now, however, physicists don’t have enough data to know exactly what kind of Higgs boson it is. Data will keep accumulating at the LHC, and the question may not be answered until the end of 2012.

To answer this, the data that needs to be accumulated is the way the Higgs boson can decay, producing one of these particle combinations: two Z bosons; two photons; two b quarks; two tau leptons; or two W bosons.

“The most important decay is the two photon decay, where both ATLAS and CMS have seen more of this decay than the Standard Model predicts,” said Christopher Hill from Ohio State University, and the deputy physics co-ordinator for CMS detector.

“If this trend continues as we add more data this year, this would be not just a discovery of the Higgs boson, but a discovery of some new physics,” he said.

The next layer of physics

“We don’t know what’s next – where the next layer of physics is going to be. The Standard Model Higgs is not going to help us,” said de Roeck.

If the Higgs boson found by CERN is exactly what the Standard Model of physics predicts, and the Higgs boson conforms exactly to the Standard Model, it will be a blow to physicists.

It will mean one of two things: either “new physics is unreachable” by high-energy experiments like the LHC, or “new physics will come from other things – not the Higgs”, explained de Roeck.

“The Higgs boson will be either the last particle of the standard model or the first particle of a new model,” he added.

The line-up waiting for the doors to open to the Higgs boson announcement in Melbourne, where 900 physicists are attending the 36th International Conference on High Energy Physics.
Credit: Jacqui Hayes/COSMOS

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