BEAMS
In the literature: open
Experimental demonstration of 6D cooling with re-acceleration
In plain words
An earlier experiment showed muons can be cooled sideways by one absorber, but not in all directions and not over many repeated stages. A full demonstration is still needed.
Precise statement
MICE demonstrated transverse (4D) emittance reduction through a single absorber without RF re-acceleration. Demonstrate net 6D emittance reduction over several cells with RF, including emittance exchange via wedges or dispersion, and measured agreement with simulation at the percent level.
What would settle it
A cooling demonstrator measuring muon-by-muon 6D emittance before and after a multi-cell channel with RF.