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Meet the LHC detectors

Discover the huge detectors, made of delicate components, that capture the sub-atomic particles from the LHC collisions.

Detecting particles

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.

Diagram from ATLAS showing possible Higgs event Candidate Higgs event in ATLAS detector. © CERN

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.

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.

Man next to large particle detector
The ATLAS detector. © CERN

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.

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.

Colourful CMS detector from CERN
The CMS detector © CERN

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 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.

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

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.

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.

Colourful view of large particle detector
CERN © View of the LHCb detector cavern.

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.

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.

Video: VELO, the vertex locator module

Hear Collider curator Dr Harry cliff introduce one of the exhbition's most beautiful objects: the vertex locator (VELO) module from CERN's LHCb detector.

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