The LHC experiments

The six experiments at the LHC are all run by international collaborations, bringing together scientists from institutes all over the world. Each experiment is distinct, characterised by its unique particle detector.

The two large experiments, ATLAS and CMS, are based on general-purpose detectors to analyse the myriad of particles produced by the collisions in the accelerator. They are designed to investigate the largest range of physics possible. Having two independently designed detectors is vital for cross-confirmation of any new discoveries made.

Two medium-size experiments, ALICE and LHCb, have specialised detectors for analysing the LHC collisions in relation to specific phenomena.

Two experiments, TOTEM and LHCf, are much smaller in size. They are designed to focus on ‘forward particles’ (protons or heavy ions). These are particles that just brush past each other as the beams collide, rather than meeting head-on

The ATLAS, CMS, ALICE and LHCb detectors are installed in four huge underground caverns located around the ring of the LHC. The detectors used by the TOTEM experiment are positioned near the CMS detector, whereas those used by LHCf are near the ATLAS detector.

ALICE :[A Large Ion Collider Experiment]

A collaboration of more than 1000 scientists from 94 institutes in 28 countries works on the ALICE experiment (March 2006).

ALICE detector
Size: 26 m long, 16 m high, 16 m wide
Weight: 10 000 tonnes
Design: central barrel plus single arm forward muon spectrometer
Location: St Genis-Pouilly, France. See ALICE in Google Earth.

ATLAS :[A Toroidal LHC Apparatus]

More than 1700 scientists from 159 institutes in 37 countries work on the ATLAS experiment (March 2006).

ATLAS detector
Size: 46 m long, 25 m high and 25 m wide. The ATLAS detector is the largest volume particle detector ever constructed.
Weight: 7000 tonnes
Design: barrel plus end caps
Location: Meyrin, Switzerland.

CMS :[Compact Muon Solenoid]

More than 2000 scientists collaborate in CMS, coming from 155 institutes in 37 countries (October 2006).

CMS detector
Size: 21 m long, 15 m wide and 15 m high.
Weight: 12 500 tonnes
Design: barrel plus end caps
Location: Cessy, France. See CMS in Google Earth.

LHCB:[Large Hadron Collider beauty]

The LHCb collaboration has 650 scientists from 48 institutes in 13 countries (April 2006).

LHCb detector
Size: 21m long, 10m high and 13m wide
Weight: 5600 tonnes
Design: forward spectrometer with planar detectors
Location: Ferney-Voltaire, France.

TOTEM :[Total Elastic and diffractive cross section Measurement]

The TOTEM experiment involves 50 scientists from 10 institutes in 8 countries (2006).
TOTEM detector
Size: 440 m long, 5 m high and 5 m wide
Weight: 20 tonnes
Design: Roman pot and GEM detectors and cathode strip chambers
Location: Cessy, France (near CMS)

LHCF : [Large Hadron Collider forward]

The LHCf experiment involves 22 scientists from 10 institutes in 4 countries (September 2006).
LHCf detector
Size: two detectors, each measures 30 cm long, 80 cm high, 10 cm wide
Weight: 40 kg each
Design:
Location: Meyrin, Switzerland (near ATLAS).

Large Hadron Collider. Credit: NY Times

We don't mean to beat a dead horse – both Fraser and Ian have already covered this topic quite thoroughly — but just in case anyone still has any fears about the Large Hadron Collider meaning the end of the world, a new report published today provides the most comprehensive evidence available to confirm that the LHC's switch-on, due on Wednesday next week, poses no threat to mankind. A copy of the report is available HERE. In a nutshell, it says nature's own cosmic rays regularly produce more powerful particle collisions than those planned within the LHC, and nothing bad has happened to Earth from those quite natural and frequent events. The LHC will be studying nature's laws in controlled experiments. So just relax and watch the LHC rap video.

The LHC Safety Assessment Group have reviewed and updated a study first completed in 2003, which dispels fears of universe-gobbling black holes and of other possibly dangerous new forms of matter, and confirms that the switch-on will be completely safe.

The report, 'Review of the Safety of LHC Collisions', published in IOP Publishing's Journal of Physics G: Nuclear and Particle Physics, proves that if particle collisions at the LHC had the power to destroy the Earth, we would never have been given the chance to exist, because regular interactions with more energetic cosmic rays would already have destroyed the Earth or other astronomical bodies.

The Safety Assessment Group compares the rates of cosmic rays that bombard Earth, other planets in our solar system, the Sun and all the other stars in our universe itself to show that hypothetical black holes or strangelets, that have raised fears in some, will in fact pose no threat.

The report also concludes that, since cosmic-ray collisions are more energetic than those in the LHC, but are incapable of producing vacuum bubbles or dangerous magnetic monopoles, we should not fear their creation by the LHC.

LHC collisions will differ from cosmic-ray collisions in that any exotic particles created will have lower velocities, but the Safety Assessment Group shows that even fast-moving black holes produced by cosmic rays would have stopped inside the Earth or other astronomical bodies. Their existence proves that any such black holes could not gobble matter at a risky rate.

As the Safety Assessment Group writes, "Each collision of a pair of protons in the LHC will release an amount of energy comparable to that of two colliding mosquitoes, so any black hole produced would be much smaller than those known to astrophysicists." They conclude that such microscopic black holes could not grow dangerously.

As for the equally hypothetical strangelets, the review uses recent experimental measurements at the Brookhaven National Laboratory's Relativistic Heavy-Ion Collider, New York, to prove that they will not be produced during collisions in the LHC.