The goal of the CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter.

[1] Over 4,000 people, representing 206 scientific institutes and 47 countries, form the CMS collaboration who built and now operate the detector.

CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals.

CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 0.9–13.6 TeV, the center-of-mass energy of the LHC particle accelerator.

This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 tesla, about 100 000 times that of the Earth.

The interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in the beam as injector magnets are activated and deactivated.

But, it is worth noting that for studies of physics at the electroweak scale, the scattering events are initiated by a single quark or gluon from each proton, and so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons (determined by the parton distribution functions).

The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points.

It is also the inner most layer of the detector and so receives the highest volume of particles: the construction materials were therefore carefully chosen to resist radiation.

As particles travel through the tracker the pixels and microstrips produce tiny electric signals that are amplified and detected.

The tracker employs sensors covering an area the size of a tennis court, with 75 million separate electronic read-out channels: in the pixel detector there are some 6,000 connections per square centimetre.

The expected HL-LHC upgrade will increase the number of interactions to the point where over-occupancy would significantly reduce track-finding effectiveness.

Lead tungstate crystal is made primarily of metal and is heavier than stainless steel, but with a touch of oxygen in this crystalline form it is highly transparent and scintillates when electrons and photons pass through it.

They are set in a matrix of carbon fibre to keep them optically isolated, and backed by silicon avalanche photodiodes for readout.

The HCAL consists of layers of dense material (brass or steel) interleaved with tiles of plastic scintillators, read out via wavelength-shifting fibres by hybrid photodiodes.

Located 11 m either side of the interaction point, this uses a slightly different technology of steel absorbers and quartz fibres for readout, designed to allow better separation of particles in the congested forward region.

It is 13 m long and 6 m in diameter, and its refrigerated superconducting niobium-titanium coils were originally intended to produce a 4 T magnetic field.

[13] The inductance of the magnet is 14 Η and the nominal current for 4 T is 19,500 A, giving a total stored energy of 2.66 GJ, equivalent to about half-a-tonne of TNT.

Made up of three layers this "return yoke" reaches out 14 metres in diameter and also acts as a filter, allowing through only muons and weakly interacting particles such as neutrinos.

Because muons can penetrate several metres of iron without depositing a significant amount of energy, unlike most particles, they are not stopped by any of CMS's calorimeters.

Cathode strip chambers (CSC) are used in the endcap disks where the magnetic field is uneven and particle rates are high.

Resistive plate chambers (RPC) are fast gaseous detectors that provide a muon trigger system parallel with those of the DTs and CSCs.

The electrodes are transparent to the signal (the electrons), which are instead picked up by external metallic strips after a small but precise time delay.

The pattern of hit strips gives a quick measure of the muon momentum, which is then used by the trigger to make immediate decisions about whether the data are worth keeping.

The forward region is the part of CMS most affected by large radiation doses and high event rates.

The GEM chambers will provide additional redundancy and measurement points, allowing a better muon track identification and also wider coverage in the very forward region.

These chambers are filled with an Ar/CO2 gas mixture, where the primary ionisation due to incident muons will occur which subsequently result in an electron avalanche, providing an amplified signal.

Particles travelling through CMS leave behind characteristic patterns, or "signatures", in the different layers, allowing them to be identified.

To have a good chance of producing a rare particle, such as a Higgs boson, a very large number of collisions is required.

Data that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sites around the world for easier access and redundancy.