What the Higgs?

Wondering what all this Higgs boson fuss is about? Here’s our guide to CERN's historic announcement...

So what’s all this excitement about a new particle?

Scientists at the Large Hadron Collider near Geneva, Switzerland today (4 July) announced that they’ve discovered a new particle – a particle which looks very much like the long sought-after Higgs boson!

The Higgs boson is a particle that was first predicted during the mid-1960s. It’s named after Professor Peter Higgs, one of the physicists who first theorised its existence.

You might also have heard it being called the ‘God Particle’ – a moniker not generally used by the scientists themselves (the term was first used in a book by Nobel prize-winning physicist Leon Lederman, who has jokingly said that it’s short for the ‘Goddamn Particle’ – a reference to the boson's frustratingly elusive nature).

According to the Standard Model of particle physics, the universe is made up of a neat set of building blocks. These include electrons and quarks, as well as heavier, force-carrying particles called bosons.

Over the years, these particles have all been confirmed by experiments. One long-enduring mystery, however, was how the particles got their mass – theory predicts that the particles in the newly-formed universe were massless. But without mass, of course, nothing would exist – no stars, no planets, and definitely no life.

One solution to this problem is the Higgs field – an invisible energy field that permeates the universe, switched on just one trillionth of a second after the Big Bang. Particles get their mass when they interact with this field, leaving behind a Higgs boson in the process. The amount of ‘drag’ the particle experiences from the Higgs field determines its mass. Photons, for example, don’t interact with the field, allowing them to zip through the cosmos at the speed of light. Heavier particles, on the other hand, move through the Higgs field like a swimmer through treacle.

To recreate the conditions that existed shortly after the Big Bang, physicists use particle accelerators to smash beams of protons together at extremely high energies.

The researchers then trawl through the wreckage of these proton-proton collisions, looking for any signs of a Higgs boson. The boson itself disappears too quickly to be detected directly, but the scientists can look for the telltale particles created when a Higgs boson decays. In order to make sure that they’ve really glimpsed the Higgs, not background fluctuations, trillions of these collisions are analysed.

Physicists in two separate CERN teams – CMS and ATLAS – have announced that they've found the strongest evidence yet for a new particle with an energy of 125 - 126 gigaelectronvolts (GeV) – around 130 times heavier than the proton.

Both teams announced a significance level of ‘5 sigma’ for their result – meaning that there’s a one-in-3.5 million chance that the findings are flukes. In other words, they’ve achieved a world first – the discovery of a Higgs-like particle.

The scientists stopped short of saying that they've actually found the Higgs boson – they don’t yet have enough data to confirm that the particle exactly matches predictions.

To find out for sure, they’ll continue smashing photons together, checking whether the decay products match up with theory. Eventually, the physicists will be able to confirm whether this new particle is indeed the Higgs, or – perhaps even more intriguingly – another boson.

Meanwhile, Professor Higgs is already preparing the celebrations: he’s reportedly asked his family to put the champagne in the fridge. You can’t blame him for wanting to get the party started though – July 4 2012 looks like being a historic day for particle physics.