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The detectors

The LHC is the largest and most powerful particle accelerator ever built. It took international teams numbering in the thousands to design, construct and operate the 27 km collider and its four giant particle detectors Collider features authentic objects from CERN, home of the LHC, from huge superconducting magnets to incredibly precise detectors used to record the passage of the tiny, invisible particles.

Inside the LHC videos | The collider | The detectors

Detecting particles

Candidate Higgs event in ATLAS detector
Candidate Higgs event in ATLAS detector. © CERN

At four points on the LHC ring, the relatively narrow tunnel housing the collider opens up into a vast underground cavern. These huge concrete spaces house the four LHC detectors, effectively super-sized digital cameras that record the millions of collisions produced by the LHC every second.

These detectors are huge, and yet made out of thousands of incredibly sophisticated and delicate components, that work together to capture information about the identities and properties of the hundreds of particles that are created in each collision.

CERN’s four detectors, graphic from the Collider exhibition
CERN’s four detectors, graphic from the Collider exhibition. © Science Museum / Northover Brown

Each of the four detectors (ATLAS, ALICE, CMS and LHCb) has their own unique technology specifically suited to the research they are intended for. Massive teams of physicists and engineers work together to build, maintain and operate these detectors, as well as to analyse the vast quantities of data that they generate.

ATLAS (A Toroidal LHC ApparatuS)

ATLAS is one of CERN’s two 'general purpose' detectors, designed to investigate a wide range of physics – from dark matter particles to the hunt for the Higgs boson.

The ATLAS detector
The ATLAS detector. © CERN

Sat in a cavern 100m underground, ATLAS is the largest detector ever built. Weighing in at 7,000 tonnes, its dimensions are staggering: 46m long, 25m high and 25m wide. The detector produces enough data to fill 100,000 CDs every second, but because of its sophisticated 'trigger' system it records only potentially interesting data – amounting to averagely 27 CDs per minute.

CMS (Compact Muon Solenoid experiment)

Situated directly opposite ATLAS on the LHC ring, CMS is CERN’s other 'general purpose' detector. The CMS and ATLAS experiments independently produced and analysed the data for the Higgs boson discovery in 2012, each confirming the others’ results.

The CMS detector
The CMS detector. © CERN

The 5 storey-high CMS experiment is one of the largest scientific collaborations in history, with 4,300 physicists, engineers and students working together on it from all over the world. At 12,500 tonnes, it is the heaviest of CERN’s four detectors, containing twice as much iron as the Eiffel Tower. Though slightly smaller than ATLAS, the cavern that houses the detector could nevertheless 'contain all the residents of Geneva' – according to the CMS website.

ALICE (A Large Ion Collider Experiment)

ALICE was designed to detect collisions from lead nuclei, rather than the LHC’s usual protons. The detector has the specific purpose of examining an extreme state of matter called 'quark-gluon plasma', which existed just after the Big Bang before protons and neutrons could form.   

View of inside the ALICE detector
View of inside the ALICE detector. © CERN

ALICE weighs a whopping 10,000 tonnes, and like CERN’s other detectors is composed of a number of sub-detectors – 18 in total. These various components each have their own job, such as detecting a specific kind of particle, or property such as energy or momentum.

LHCb (Large Hadron Collider beauty experiment)

The 4,500-tonne LHCb detector is a highly specialised device designed to study one particle in particular – the so-called 'bottom', 'beauty' or sometimes simply 'b' quark. LHCb looks for the minute differences between b quarks and anti-b quarks in order to learn more about the subtle asymmetry between matter and  its 'mirror-image', antimatter.

View of the LHCb detector cavern
View of the LHCb detector cavern. © CERN

Like CMS and ALICE, LHCb is located on the French side of the LHC’s 27-km ring, 100 metres beneath the village of Ferney-Voltaire. At the heart of LHCb is the incredibly precise and delicate Vertex Locator (VELO), the closest detector to the enormously energetic LHC beams anywhere on the ring.