Fervent Freyja said:
They have been around for a while now.
http://nucla.physics.ucla.edu/sites/default/files/kmahn_ucla_accnu_v1.pdf
While these are indeed beams of neutrinos (though with huge size and ##\Delta E## compared to beams of charged particles), they aren't well-defined, narrow,
accelerated beams, which is what the OP was asking. These are beams that are produced by reactions of accelerated charged particles. Once you produce neutrinos via pion decay, the energy you have is the energy you get. You can't manipulate them.
The story is similar in neutron beams. Given, say, a thermal flux of neutrons from a reactor, you can use collimators and monochromators to restrict the size and energy of the neutrons by essentially filtering out unwanted energies, but you cannot accelerate them. You can also produce high energy neutrons in nuclear reactions, but like the neutrino case, it's the reaction and velocity of the accelerated charged particles that determines the velocity of the neutrons.
Of course, neutrons have a magnetic moment, so you can manipulate them through their magnetic moment. But in most cases this effect is negligible. The exception is ultracold neutrons, which are very very slow, so the effect is non-negligable. They are slow enough (neV) that you can trap them. This trapping process involves de-accelerating the neutrons. Naturally, the same method can also be used to accelerate them, but only to a small extent (until they were no longer ultracold). The limiting factor is magnet strength.
