The Hunt for the Higgs Boson

CERN

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.

Invisible field
Back in the 1960s, physicists were formulating a governing principle to explain how fundamental particles - the building blocks of all matter in the universe - interact. But their theory hit a wall. If they took into account the mass of these particles, the principle fell apart. The physicists knew that particles must have mass in order to form solid, stable structures. Then, in 1964, three groups of scientists proposed a solution to the conundrum. What if an invisible field pervades everything, giving the particles mass as they move through it and interact with it? They called this field the Brout-Englert-Higgs (BEH) field.

In July 1964, British theoretical physicist Peter Higgs submitted two articles to a scientific journal, the second of which set out his ideas on the Higgs mechanism.

But it was categorically rejected by the journal as being 'of no obvious relevance to physics'.

Undeterred, he forwarded the manuscript to another journal, adding a short paragraph in which he predicted the existence of a new particle associated with the mechanism: the Higgs boson.

Phantom particle

Higgs' ideas took hold, and a decade later, they were a widely accepted feature of the standard model of particle physics.

But for the mechanism to be proven, physicists needed to find the Higgs boson through experimentation.

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 biggest machine on Earth
In the late 1970s, CERN decides to build a large electron-positron collider (LEP) inside a 27-km long tunnel.

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.

Meanwhile, after CERN's 1983 landmark discovery of the W and Z bosons, which carry the weak force - one of four fundamental forces that govern all matter in the universe - the scientific adviser to the US President called for the country to regain its leadership in high-energy physics.

US physicists proposed a new 87km-circumference 'superconducting super collider' (SSC) that would be twice as powerful as the LHC.

The plan was endorsed by President Reagan in January 1987 to the tune of $4.4 billion. A site was selected near Dallas, Texas.

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.

Goddamn particle!
In 1993, Leon Lederman, Director of Fermilab - the largest particle physics laboratory in the US - published a book about the Higgs boson. When quizzed about its title, he said “[The Higgs boson] is so central to the state of physics today…that I have given it a nickname: the God particle.... The publisher wouldn’t let us call it goddamn particle, though that might be a more appropriate title given its villainous nature and the expense it is causing.”

The same year, a request for funding the UK's participation in the LHC prompted UK Science Minister William Waldegrave to offer a bottle of vintage champagne to whoever could explain the Higgs boson in layman's terms on a piece of A4 paper.

This is the winning submission, including a cartoon and an analogy about a crowded party, by David J Miller from University College London.

In this section, the Higgs boson is compared to a rumour spreading through a room.

The analogy is that the rumour (the Higgs boson) represents the interaction of the cocktail guests (the Higgs field) among themselves.

All systems go
After years of discussion and planning within CERN member states, the CERN council finally approved the LHC project on 16 December 1994. With further contributions from Japan, the USA, India and other states, a single-stage construction of the LHC is approved in1996. Six CERN Directors General led the project from conception to completion.

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.

The LHC lies along a 27km-long tunnel, 50-175m below the Swiss-French border.

Its components include 1232 blue 'dipole' magnets that bend particles along their circuit, 392 grey 'quadrupole' magnets that help align particle beams, and radio frequency cavities that accelerate the protons.

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."

Credits: Story

CERN
Paulina Mlynarska
Rolf Landua

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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