How does cern detect neutrinos

Colliders copiously produce both neutrinos and anti-neutrinos of all flavors and most are produced at very high energies where neutrino interactions are not well studied. Collider neutrinos are therefore highly complementary to those from other sources. Nevertheless, the highest energy collider neutrinos and therefore the ones with the largest interaction cross sections are produced along the beamline.

Most collider detectors, however, have holes along the beamline to allow the passage of the beams, making them blind to this region. As a result, they miss the enormous flux of high-energy neutrinos streaming down the beam pipe.

The first calorimeter layer is designed to measure the energies of electrons and photons with great precision. Since these particles interact electromagnetically, it is called an electromagnetic calorimeter ECAL. Particles that interact by the strong force, hadrons, deposit most of their energy in the next layer, the hadronic calorimeter HCAL.

The only known particles to penetrate beyond the HCAL are muons and weakly interacting particles such as neutrinos. Muons are charged particles, which are then tracked further in dedicated muon chamber detectors.

Their momenta are also measured from the bending of paths in the CMS magnetic field. Neutrinos, however, are neutral and since they hardly interact at all they will escape detection. Their presence can nevertheless be inferred. A typical emulsion detector consists of silver bromide crystals with diameters of nm dispersed in gelatin media. Each crystal works as an independent detection channel. It will be on the collision axis line of sight LOS to maximize the number of neutrino interactions.

Figure 4 shows a magnified view of the neutrino detector modules. The detector is composed of a repeated structure of emulsion films interleaved with 1-mm-thick tungsten plates. The tungsten target was chosen because of its high density and short radiation length, which helps keep the detector small, localizing electromagnetic showers to a small volume.