When protons meet head-on at the Large Hadron Collider (LHC), the collisions provide a micro-laboratory to investigate many phenomena, including the protons themselves. This is the physics that the TOTEM experiment is designed to explore, by taking precise measurements of protons as they emerge from collisions at small angles. This region is known as the 'forward' direction and is inaccessible by other LHC experiments.
As CERN's 'longest' experiment, TOTEM detectors are spread across almost half a kilometre around the CMS interaction point. TOTEM has almost 3,000 kg of equipment, including four particle 'telescopes' as well as 26 'Roman pot' detectors.
The 'telescopes' – T1 and T2 – use cathode-strip chambers and Gas Electron Multipliers (GEM) to track the particles emerging from collisions at the CMS interaction point. Meanwhile, 'Roman Pots' with silicon sensors perform measurements of scattered protons. Named for their shape and first use by physicists from Rome in the 1970s, 'Roman Pots' are unique for their ability to move sensors both vertically and horizontally in the accelerator vacuum.
In 2015, the TOTEM and CMS collaborations will coordinate the use of their detectors to perform combined measurements. This new level of collaboration will lead to results of unprecedented accuracy, including measurements of the invariant mass created in the collision.
The TOTEM experiment involves about 100 scientists from 16 institutes in 8 countries (August 2014).