What is LHC ?

The CERN Fire and Rescue remit covers 40km of underground tunnels, radiation and chemical risks as well as the buildings above ground. CERN firemen train in abseiling and rope rescue techniques in preparation for a tunnel emergency.

In 2003, 6.1% of traffic at Geneva International Airport was related to CERN, a total of 54 868 passengers.

X-ray and radiopharmaceutical techniques in medical imaging were developed by particle physicists, as was radiotherapy for cancer patients.

Particle accelerators are used to dry the paint on soft drinks cans.

The Large Hadron Collider (LHC) is the world's largest and most powerful particle collider and the largest machine in the world.

It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries.

It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.

Its first data-taking period lasted from March 2010 to early 2013 at an energy of 3.5 to 4 teraelectronvolts (TeV) per beam (7 to 8 TeV total), about four times the previous world record for a collider and accelerator.

Afterwards, the accelerator was taken offline and upgraded over the course of two years. It was restarted in early 2015 for its second research run, reaching 6.5 TeV per beam (13 TeV total, the present world record). At the end of 2018, it entered a second two-year shutdown period.

The aim of the LHC is to allow physicists to test the predictions of different theories of particle physics, including measuring the properties of the Higgs boson and searching for the large family of new particles predicted by supersymmetric theories, as well as other unsolved questions of physics.

The collider has four crossing points, around which are positioned seven detectors, each designed for certain kinds of research. The LHC primarily collides proton beams, but it can also use beams of heavy ions. Lead–lead collisions took place in 2010, 2011, 2013, 2015 and 2018, proton–lead collisions were performed for short periods in 2013 and 2016, and a short run of xenon–xenon collisions took place in 2017.

The LHC's computing grid is a world record holder. Data from collisions were produced at an unprecedented rate for the time of first collisions (tens of petabytes per year), a major challenge at the time, to be analysed by a grid-based computer network infrastructure connecting 170 computing centres in 42 countries as of 2017 – by 2012 the Worldwide LHC Computing Grid was also the world's largest distributed computing grid, comprising over 170 computing facilities in a worldwide network across 36 countries

Physicists hope that the Large Hadron Collider will help answer some of the fundamental open questions in physics, concerning the basic laws governing the interactions and forces among the elementary objects, the deep structure of space and time, and in particular the interrelation between quantum mechanics and general relativity.

Data are also needed from high-energy particle experiments to suggest which versions of current scientific models are more likely to be correct – in particular to choose between the Standard Model and Higgsless model and to validate their predictions and allow further theoretical development. Many theorists expect new physics beyond the Standard Model to emerge at the TeV energy level, as the Standard Model appears to be unsatisfactory. Issues explored by LHC collisions include.

Is the mass of elementary particles being generated by the Higgs mechanism via electroweak symmetry breaking It was expected that the collider experiments will either demonstrate or rule out the existence of the elusive Higgs boson, thereby allowing physicists to consider whether the Standard Model or its Higgsless alternatives are more likely to be correct

is supersymmetry, an extension of the Standard Model and Poincaré symmetry, realized in nature, implying that all known particles have supersymmetric partners

It is already known that electromagnetism and the weak nuclear force are different manifestations of a single force called the electroweak force. The LHC may clarify whether the electroweak force and the strong nuclear force are similarly just different manifestations of one universal unified force, as predicted by various Grand Unification Theories.

The LHC is the world's largest and highest-energy particle accelerator. The collider is contained in a circular tunnel, with a circumference of 26.7 kilometres (16.6 mi), at a depth ranging from 50 to 175 metres (164 to 574 ft) underground.

The 3.8-metre (12 ft) wide concrete-lined tunnel, constructed between 1983 and 1988, was formerly used to house the Large Electron–Positron Collider

The collider tunnel contains two adjacent parallel beamlines (or beam pipes) each containing a beam, which travel in opposite directions around the ring.

The beams intersect at four points around the ring, which is where the particle collisions take place. Some 1,232 dipole magnets keep the beams on their circular path (see image), while an additional 392 quadrupole magnets are used to keep the beams focused, with stronger quadrupole magnets close to the intersection points in order to maximize the chances of interaction where the two beams cross

Magnets of higher multipole orders are used to correct smaller imperfections in the field geometry.

In total, about 10,000 superconducting magnets are installed, with the dipole magnets having a mass of over 27 tonnes.

Approximately 96 tonnes of superfluid helium-4 is needed to keep the magnets, made of copper-clad niobium-titanium, at their operating temperature of 1.9 K (−271.25 °C), making the LHC the largest cryogenic facility in the world at liquid helium temperature.