Neutrino Detection

Neutrino Detection

We can only detect the presence of a neutrino in our experiment if it interacts. Neutrinos interact in two ways charged-current interactions, where the neutrino converts into the equivalent charged lepton (e.g. inverse beta decay, ν+ p → n + e ) – the experiment detects the charged lepton; neutral-current interactions,

where the neutrino remains a neutrino, but transfers energy and momentum to whatever it interacted with we detect this energy transfer, either because the target recoils (e.g. neutrino-electron scattering, ν + e → ν + e) or because it breaks up (e.g. H + ν → p + n + ν). Charged-current interactions occur through the exchange of a W particle, neutral- current through the exchange of a Z .

In principle, charged-current interactions are easier to work with, because electrons and moons have characteristic signatures in particle detectors and are thus fairly easy to identify. They also have the advantage that they “flavor-tag” the neutrino if an electron is produced, it came from an electron-neutrino. However, there must be enough available energy to allow the mass of the lepton to be created from E = mc – this means that for very low- energy neutrinos (e.g. solar and reactor neutrinos) charged-current interactions are only possible for electron- neutrinos. Various different detector technologies have been used in neutrino experiments over the years, depending on the requirements of the particular study. Desirable features of a neutrino experiment will typically include several of the following:

low energy threshold, so that low-energy neutrinos can be detected and studied (especially for solar neutrinos); good angular resolution, so that the direction of the detected particle can be accurately reconstructed (especially for astrophysical  neutrinos) good particle identification, so that electrons and moons can be well separated (essential for oscillation experiments); good energy measurement, so that the energy of the neutrino can be reconstructed (useful for oscillation measurements and astrophysics); good time resolution, so that the time evolution of transient signals can be studied (essential for supernova neutrinos, and important for other astrophysical sources); charge identification, so that leptons and ant leptons can be separated (will be essential for neutrino factory experiments).

It is not possible to have all of these things in one experiment – for example, experiments with very low energy threshold tend not to have good angular or energy resolution. Neutrino physicists will select the most appropriate technology for the aims of their particular experiment.