M. Schwartz and B. Pontecorvo proposed to exploit accelerators to produce neutrinos in 1960.
The experiment, first carried out by Lederman, Schwartz, Steinberger and collaborators demonstrated the existence of two neutrino flavors.
Modern experiments steer the protons outside the accelerator and focus the particles produced after the target by magnetic horns or a static focusing system based on quadrupoles and dipoles.
At large distances from the end of the tunnel, no particles are present except for an intense flux of neutrinos.
In early experiments, the flux of neutrinos was estimated by measuring the number of pions produced after the target and monitoring the muons produced at the end of the tunnel.
After the discovery of neutrino oscillation, the need for high precision beams fostered the construction of sophisticated monitoring systems.
They are based on dedicated experiments to measure the number of particles produced by proton interactions on solid-state targets (beryllium, graphite).
The beamline comprises the proton beam, target, focusing system, and decay tunnel, and it is simulated by Monte Carlo methods.
Variations of the flux are monitored in real-time by measuring the number of protons impinging on the target and the rate of muons.
All these techniques are the basic toolkit of accelerator neutrino physicists and are inherited by beam diagnostics.
Similarly, an electron neutrino produced by a kaon decay -for instance
Current neutrino beams record muons but they have not reached single-particle sensitivity.
Monitored neutrino beams detect the charged leptons produced in the decay tunnel but the experimenters do not attempt to identify simultaneously the charged lepton and the neutrino produced by the decay of the parent particle.
These facilities are called (time) tagged neutrino beams and were proposed by L.N.