Deep underground below the French-Swiss border, CERN scientists collide particles into one another at the speed of light, inside the largest machine on Earth. The Large Hadron Collider recreates the conditions of the universe a fraction of a second after the Big Bang. Find out how the revolutionary discovery of the Higgs boson was made here.
4 July 2012. There's a palpable sense of anticipation as scientists squeeze into every seat in CERN's auditorium.
A major announcement is due about the Large Hadron Collider's ATLAS and CMS experiments - one that will lose Stephen Hawking $100 in a bet.
Needle in a haystack
Finding the particle would be next to impossible: even if it existed, it would only occur once in a billion or so proton-to-proton collisions.
The idea for CERN's future proton-proton collider was first debated at a workshop in Lausanne in 1984.
Using the existing LEP tunnel would keep costs down, but the new collider would need powerful new superconducting magnets to keep particles on track before colliding them at close to the speed of light.
Back in France, in March 1992, 650 physicists assembled to plan how LHC experiments could compete with the more powerful SSC. Detectors would need to run at a collision rate ten times that of the SSC, needing technology far beyond what was possible in the 1980s. A decade of intense R&D ensued, leading eventually to the construction of the LHC experiments.
By May 1990, the projected cost of the SSC had risen to $7.9 billion.
Spiraling costs and continued funding problems eventually led to the entire SSC project being scrapped in October 1993.
In 1997, with the LEP accelerator still operational, civil engineering for the ATLAS cavern began.
LEP is dismantled in 2001 and the caverns are prepared for installation of the LHC magnets and four huge LHC detectors.
ATLAS is a general-purpose detector designed to cover the widest possible range of physics at the LHC.
The main feature of the detector is its enormous doughnut-shaped magnet system.
ATLAS is the largest-volume detector ever constructed at 46m long, 26m high and 26m wide, with a weight of 7000 tonnes.
The ATLAS collaboration involves nearly 3000 scientific authors from 182 institutions across 38 countries, as of January 2017.
CMS is a general-purpose detector with similar physics goals to those of ATLAS, but different design and technology.
It is built around a huge superconducting electromagnet called a solenoid.
The detector is 21m long, 15m high and 15m wide and weighs 12500 tonnes.
The CMS collaboration comprises more than 3500 scientists, engineers and students from 201 institutes in 36 countries, as of January 2017.
The search for the Higgs boson began in earnest in the early 1980s, using bigger accelerators with higher collision energies.
Competition between CERN's LEP collider and Fermilab's Tevatron particle accelerator made big progress in narrowing down the possible mass of the Higgs boson.
Theory states that one in several billion proton-proton collisions will produce a Higgs boson. And then it must be detected, for example through its decay into two photons. The LHC produces about 1 billion collisions per second. In total, more than 2000 trillion collisions were measured by 4 July 2012.
The vast amount of data from the detectors is analysed using a network of several hundred thousand computers in the worldwide LHC grid. Thousands of scientists in ATLAS and CMS search for specific patterns in the reconstructed events. This histogram shows the mass distribution for collisions producing two high-energy photons. A small but significant bump emerges at about 125 GeV when adding up all the data - the first proof for the existence of the Higgs boson!
On 4 July 2012, both ATLAS and CMS announce a discovery - a statistically significant signal from a particle fitting the description of the Higgs boson. Further measurements confirmed the predicted properties. Francois Englert and Peter Higgs receive the 2013 Nobel prize in physics.
On hearing the news, Stephen Hawking, said: "This is an important result ... it is a pity in a way because the great advances in physics have come from experiments that gave results we didn't expect. For this reason I had a bet with Gordon Kane of Michigan University that the Higgs particle wouldn't be found. It seems I have just lost $100."