Peter Higgs, physicist from the Edinburgh University was the first to propose the idea of a strange particle named "The Higgs boson" (after his name) back in 1964. Higgs was invited to Geneva to celebrate the possibility of the scientific discovery of this theoretical particle, widely known as "The God particle" (???)
The first experiments began at Fermilab's Tevatron until its close in late 2011, but another experiment began in 2010 in CERN. Two experiments were running in CERN for this reason, the ATLAS and the CMS. The LHC was designed to provide the enormous amount of energy required for the bosom to appear. The mathematical models had predicted that 1.4 TeV are required, so the LHC was designed to collide 2 proton beams each one at 0.7 TeV. Just for the reference, 1 eV is the amount of energy that one electron gains by charge moving inside an electric potential difference of 1 Volt. 1 eV is equal to 1.602×10"1219 joule.
On 4 July 2012, both ATLAS and CMS reported independently that they discovered a new particle with mass of around 125 GeV/c2 (in the order of 10-25 kgs), which is equal to 133 proton masses. This particle carries the basic characteristics of the Higgs boson!
What is the Higgs Boson in plain words? Why is it so important?
Before, we need to explain what "mass" is. In physics, mass is a quantitative measure of an object's resistance to acceleration. To understand what the boson is, you need to understand first what mass is. We call something "heavy" because it has a lot of "mass", but mass itself has nothing to do with weight at all. A man that weights 60 kilos on earth, the same man weights 10 kilos on the moon, though his mass is the same!. So, weight is the result of the gravity on the object's mass, do not confuse it. Mass is the resistance to acceleration of an object. Up until now, we could not determine how mass is created.
Even in a weightless environment, and object may have 0 weight but a lot of mass. The spaceship Enterprise for example would weight 0 kilos in the open space, still it would require a lot of power to accelerate it through space because of its mass. And though we know how to calculate this "drag" and put the appropriate engines on the spaceship, we did not really know where this drag comes from. So we did not know where mass comes from.
In early universe, little after the Big Bang, there were only tiny particles such as quartz, electrons and muons. The first picoseconds of creation, all particles were moving at the speed of light, which means that they had no mass. So there had to be something there that could hold this particle soup together to form mass.
And here comes the Higgs field. The Higgs field is composed by the Higgs particles. Some particles interact with this field and they slow down their speed, while some others don't. Particles that are completely weightless will not interact at all so they won't slow down. These are the photons, and this explains also why light travels with the speed of light everywhere in the universe. The heavier a particle is, the more it interacts with the field, thus the more it slows down its speed. This is exactly the reason why particles slow down, this explains why nothing but light can travel at the speed of light, and this is the reason why the Enterprise will require a lot of power to accelerate it even in a weightless environment.
Here is one video with Fermilab scientist Don Lincoln explaining the nature of the Higgs boson
Theoretical physicist John Ellis answers the question "What is the Higgs boson?"
And here is a simpler explanation from Ian Sample from the Guardian:
How hard is it to detect these particles?
There are two main difficulties: First of all, we need to create these particles. This is the job of the LHC. Proton beams are accelerated into the LHC nearly the speed of light. These beams are very small, but the energy they require to get to that speed is enormous. Enormous is also the energy that they have. When these beams collide, the energy released from the collision is enough to excite the Higgs field. When this field is excited, Higgs bosons are created.
The second part is the most difficult. Bosons are extremely reactive with smaller particles. They have a mass of about 130-133 proton masses, and they almost instantaneously decay to smaller particles. This is the nature of these particles. Within nanoseconds after being created, they decay into either 2 photons, or into W and Z particles, or into quarks. So it is very difficult to detect them because we cannot sustain them as bosons into the detectors.
Photo: wikipedia: One possible signature of a Higgs boson from a simulated proton 13proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines