Two-decade journey for collider

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The Large Hadron Collider is the world's largest and most powerful particle accelerator. (Photograph: CERN)
The Large Hadron Collider is the world's largest and most powerful particle accelerator. (Photograph: CERN)

This year, three experiments at the Large Hadron Collider (LHC) celebrate their 20th anniversary, a year after the discovery of a particle that is expected to change physics and open an era of new scientific understanding.

The LHC is the world's largest and most powerful particle accelerator. It first started up on 10 September 2008, and remains the latest addition to the European Organisation for Nuclear Research's (CERN's) accelerator complex. The LHC consists of a 27km ring of superconducting magnets with a number of accelerating structures to boost the energy of the particles along the way.

The £2.6 billion "Big Bang" particle accelerator at the centre of the hunt for the Higgs Boson, the LHC, has been dubbed the world's largest experiment and is housed at CERN, in Switzerland. In a statement released to mark the 20-year journey, CERN says the LHC experiments involve "some of the largest and most complex experimental apparatus ever devised".

The experiments "rely on large collaborations of physicists and engineers from all over the globe, and their conception, design and construction took years - even decades - to complete. This year, three of them celebrate their 20th anniversaries."

In June 1993, Atlas and the Compact Muon Solenoid (CMS), the two general-purpose experiments at the LHC, received a provisional go-ahead to submit technical proposals, which CERN says "was the start of a difficult, but amazing path to last year's major discovery of a Higgs Boson".

Technical proposals for Atlas and CMS were submitted in 1995 and approval was granted the next year. The formal approval for construction was given on 1 July 1997 by the then director-general, Chris Llewellyn Smith, based on the recommendations of the research board and the LHC committee.

Two other LHC experiments, Alice and LHCb, also have their origins around the same time. Alice submitted a letter of intent to the LHC committee in March 1993, while LHCb's letter came two years later.

Scientific inroads

Last July, scientists said two Switzerland-based research projects had discovered a Higgs-like particle. The Higgs particle - or boson - is named after Peter Higgs, who was one of six authors who theorised about the existence of the particle in the 1960s. It is commonly called the "God Particle", after the title of Nobel physicist Leon Lederman's "The God Particle: If the Universe Is the Answer, What Is the Question?" according to Wikipedia.

Professor Simon Connell, from the University of Johannesburg's School of Physics, has said the particle is now considered to be a Higgs Boson, which could be either the missing piece of the Standard Model of Physics - a set of rules that outlines the fundamental building blocks of the universe, such as protons, electrons and atoms - or it could be one of several such Bosons leading to physics beyond the Standard Model.

Last month, CERN said it would go temporarily offline in a bid to increase its capacity and explore unknown aspects of physics.

Atlas investigates a range of physics, from the search for the Higgs Boson to extra dimensions and particles that could make up dark matter, while the CMS, which has the same set of scientific goals, uses different technical solutions and a different magnet-system design.

Connell has said the two years of downtime will lead to the LHC ultimately going beyond initial design capacity and produce copious amounts of Higgses for study. The experiment will run until 2030 and will be upgraded to 10 times its initial design specification, with the ability to collect 100 times more data, and - in the two years of down time - scientists will develop analysis tools and analyse data, he adds.

As part of the shutdown, up to 18 superconducting magnets on the LHC will be replaced, including 15 dipole magnets three and quadrupole magnet assemblies. Quadrupole magnets help to focus the particles into a tight beam so they are more likely to collide in greater numbers as they reach the LHC detectors, says CERN.

Each quadrupole has four magnetic poles arranged symmetrically around the beam pipe to squeeze the beam either vertically or horizontally.

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