In particle physics, colliders, though harder to construct, are a powerful research tool because they reach a much higher center of mass energy than fixed target setups.

[17] Many physicists hope that the Large Hadron Collider will help answer some of the fundamental open questions in physics, which concern the basic laws governing the interactions and forces among elementary particles and the deep structure of space and time, particularly the interrelation between quantum mechanics and general relativity.

The variation in depth was deliberate, to reduce the amount of tunnel that lies under the Jura Mountains to avoid having to excavate a vertical access shaft there.

A tunnel was chosen to avoid having to purchase expensive land on the surface and to take advantage of the shielding against background radiation that the Earth's crust provides.

Here, the proton bunches are accumulated, accelerated (over a period of 20 minutes) to their peak energy, and finally circulated for 5 to 24 hours while collisions occur at the four intersection points.

The ATLAS and CMS experiments discovered the Higgs boson, which is strong evidence that the Standard Model has the correct mechanism of giving mass to elementary particles.

[50] In August 2011, a second application (Test4Theory) went live which performs simulations against which to compare actual test data, to determine confidence levels of the results.

[60][61] Its first run discoveries included the long-sought Higgs boson, several composite particles (hadrons) like the χb (3P) bottomonium state, the first creation of a quark–gluon plasma, and the first observations of the very rare decay of the Bs meson into two muons (Bs0 → μ+μ−), which challenged the validity of existing models of supersymmetry.

[62] The size of the LHC constitutes an exceptional engineering challenge with unique operational issues on account of the amount of energy stored in the magnets and the beams.

The "training" process involves repeatedly running the magnets with lower currents to provoke any quenches or minute movements that may result.

[55] The LHC successfully completed its major test: after a series of trial runs, two white dots flashed on a computer screen showing the protons travelled the full length of the collider.

[85] CERN next successfully sent a beam of protons in an anticlockwise direction, taking slightly longer at one and a half hours owing to a problem with the cryogenics, with the full circuit being completed at 14:59.

It estimated that repairs would take at least two months, owing to the time needed to warm up the affected sectors and then cool them back down to operating temperature.

[93] Most of 2009 was spent on repairs and reviews from the damage caused by the quench incident, along with two further vacuum leaks identified in July 2009; this pushed the start of operations to November of that year.

A run with lead ions started on 8 November 2010, and ended on 6 December 2010,[97] allowing the ALICE experiment to study matter under extreme conditions similar to those shortly after the Big Bang.

The LHC was shut down on 13 February 2013 for its two-year upgrade called Long Shutdown 1 (LS1), which was to touch on many aspects of the LHC: enabling collisions at 14 TeV, enhancing its detectors and pre-accelerators (the Proton Synchrotron and Super Proton Synchrotron), as well as replacing its ventilation system and 100 km (62 mi) of cabling impaired by high-energy collisions from its first run.

[115] An initial focus of research was to investigate the possible existence of the Higgs boson, a key part of the Standard Model of physics which was predicted by theory, but had not yet been observed before due to its high mass and elusive nature.

[60] Some extensions of the Standard Model predict additional particles, such as the heavy W' and Z' gauge bosons, which are also estimated to be within reach of the LHC to discover.

[135] After the first year of data collection, the LHC experimental collaborations started to release their preliminary results concerning searches for new physics beyond the Standard Model in proton–proton collisions.

[120] Between July and August 2011, results of searches for the Higgs boson and for exotic particles, based on the data collected during the first half of the 2011 run, were presented in conferences in Grenoble[143] and Mumbai.

Both the CMS and ATLAS detectors have also shown intensity peaks in the 124–125 GeV range, consistent with either background noise or the observation of the Higgs boson.

[123] On 4 July 2012, both the CMS and ATLAS teams announced the discovery of a boson in the mass region around 125–126 GeV, with a statistical significance at the level of 5 sigma each.

[150] On 8 November 2012, the LHCb team reported on an experiment seen as a "golden" test of supersymmetry theories in physics,[126] by measuring the very rare decay of the

[178] The upgrade aims at increasing the luminosity of the machine by a factor of 10, up to 1035 cm−2s−1, providing a better chance to see rare processes and improving statistically marginal measurements.

It is CERN's opening bid in a priority-setting process called the European Strategy for Particle Physics Update, and will affect the field's future well into the second half of the century.

The Large Hadron Collider gained a considerable amount of attention from outside the scientific community and its progress is followed by most popular science media.

[188][189] National Geographic Channel's World's Toughest Fixes, Season 2 (2010), Episode 6 "Atom Smasher" features the replacement of the last superconducting magnet section in the repair of the collider after the 2008 quench incident.

The episode includes actual footage from the repair facility to the inside of the collider, and explanations of the function, engineering, and purpose of the LHC.

Lead singer Isaac Slade said in an interview with The Huffington Post, "There's this large particle collider out in Switzerland that is kind of helping scientists peel back the curtain on what creates gravity and mass.

[193] The movie version of the book has footage filmed on-site at one of the experiments at the LHC; the director, Ron Howard, met with CERN experts in an effort to make the science in the story more accurate.