The Science of TOTEM

Part of the TOTEM detector
Part of the TOTEM detector. Image © CERN
TOTEM may be a small experiment with about 100 collaborators, but it has the potential to make unique observations at the LHC. The experiment measures particles scattering at very small angles from the LHC's proton-proton collisions, allowing scientists to study physical processes that can’t be studied by the other LHC experiments, such as how the shape and size of a proton varies with energy.

TOTEM scientists study inelastic proton-proton collisions in which one proton survives and the other disintegrates and produces "debris" that continues traveling forward. They also measure elastic collisions in which both protons survive and only slightly deflect each other.

To examine both types of collisions, TOTEM scientists rely on particle detectors that are located near the collision point in the center of the much-larger CMS detector. The TOTEM detectors are placed close to the beam, both inside the CMS detector and far outside of it—more than 100 meters away from the collision point.

By counting the glancing collisions, TOTEM will determine the total proton-proton collision probability at the LHC. This number, called the total cross section, is critical for determining the probability of producing certain particles—such as the much-sought-after Higgs boson—in LHC collisions. Data provided by TOTEM also allow scientists to calculate the LHC's luminosity, or its rate of producing collisions.

Together, the TOTEM and CMS detectors cover the whole range of scattering angles, which has never before been done in a hadron collider.