The "Total elastic and diffractive cross-section measurement" experiment (TOTEM) studies forward particles to focus on physics that is not accessible to the general-purpose experiments. Among a range of studies, it measures, in effect, the size of the proton, and accurately monitors the luminosity of the Large Hadron Collider (LHC). Luminosity is the number particles per unit area per time, taking into account the target‘s penetrability to electromagnetic radiation.
To do this TOTEM must be able to detect particles produced very close to the LHC beams. It includes detectors housed in specially designed vacuum chambers called “Roman pots'” connected to the beam pipes in the LHC. There are eight Roman pots placed in pairs at four locations on either side of the collision point of the CMS experiment.
Although the two experiments are scientifically independent, TOTEM complements the results from the CMS detector and from other LHC experiments.
The 20-tonne TOTEM detector is made up of gas-electron-multiplier detectors and cathode strip chambers, in addition to the 8 Roman pots. The experiment spans 440 m, and the main detector is 5m high and 5m wide. It is located below ground near the CMS detector in Cessy, France.
The TOTEM experiment involves 143 scientists from 9 institutes in 7 countries (February 2012).