Does the Higgs boson exist?

(The existence of this page on my website is purely a reflection of my interest in the subject. The only connection Higgs Boson Communications Ltd has with the hunt for the Higgs particle is that I used to work on CERN Courier magazine.)

The 'Higgs boson' is a hypothetical (at the time of writing) particle which, if it exists, will help to explain why particles have mass. It is so central to physicists' 'standard model' of fundamental particles that it has been nicknamed 'the God particle'.
The idea was posited in 1964 by Prof. Peter Higgs at Edinburgh University, but after more than 40 years scientists still disagree on the existence of this tiny particle.
Several huge ’atom smasher’ experiments have been built to search for the Higgs, including the Large Hadron Collider (LHC) at CERN in Geneva.
On 4 July 2012, scientists at CERN announced results from two separate LHC experiments that indicate the discovery of a new sub-atomic particle. However, there is still some doubt as to whether this new particle is the Higgs boson. Joe Incandela, the leader of the team using the CMS detector on the LHC, said: “The results are preliminary but the 5 sigma signal at around 125 GeV we're seeing is dramatic. This is indeed a new particle. We know it must be a boson and it's the heaviest boson ever found. The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks.”
What does a “5 sigma signal” mean? Prof. Brian Cox summed it up: “It roughly means that you're 99.9999% sure.”
Further research is required, though CERN scientists are hopeful they may be able to confirm the existence of the Higgs boson in the next few months.

A very brief history
Researchers at the LEP (Large Electron Positron Collider, a predecessor of the LHC) at CERN claimed in September 2000 that they had found the Higgs. Unfortunately they had mashed their maths and subsequently retracted the claim. The following year John Swain (Northeastern University in Boston, member of the Electroweak Working Group at CERN) told New Scientist: "It's more likely than not that there is no Higgs."
Prof. Stephen Hawking has been one of the most prominent disbelievers. In fact he won a $100 bet with an American professor when the LEP experiment failed to provide proof. Hawking's pronouncements provoked an outburst from the retired Prof. Higgs in September 2002, which briefly hit the headlines. This attack on Hawking seemed uncharacteristic from a man so modest that he is embarrassed by the name 'Higgs boson' – he usually calls it the 'scalar boson' or 'the so-called Higgs particle' himself. However, following CERN’s 4 July 2012 announcement Hawking has happily paid up on a similar bet.
The particle – whatever its name – has been hunted by Fermilab as well as by the LHC. The LHC went live on 10 September 2008 specifically to hunt the Higgs.
For those scared by speculation about what might happen in the LHC – such as the suggestion the LHC may produce a mini-blackhole that will swallow the Earth – there is reassurance in this safety report.

More information
You can read more about the Higgs boson at CERN, or Wikipedia (which has further useful links).
Or watch a brief video explanation of the Higgs boson by my former colleague Guardian science writer Ian Sample.