How can Holmlid tell by time of flight?
It's summarily described in the paper I linked above. A form of laser-induced mass spectrometry is employed. To put it simply, when the laser pulse is applied on the target where UDH is expected to be, UDH fragments are ejected and then detected with a custom-made detector assembly inside the vacuum chamber. From the time it takes for these fragments to arrive to the detector and some safe assumptions, their kinetic energy and structure can be inferred.
The non-superfluid phase of UDH is more tightly bound and only forms small clusters, and will produce the fastest fragments arriving earlier at the detector. They cause the narrow peak at the beginning of the charts, and are always present. The superfluid phase will form larger fragments which will arrive a bit later at the detector; it disappears above a certain temperature, possibly reverting to ordinary hydrogen atoms or hydrogen Rydberg matter.
Each line is a test at different temperature:
EDIT: note that other tests were done in other papers to determine that a superfluid phase was observed, it's not just based on these results alone.
What are those particles with spiral tracts that Sveinn sees in his cloud chamber after the laser pulse?
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Those have to be something different with hundreds MeV of energy or more. The time-of-flight results above are instead for particles with much lower energies, in the hundreds of eV range maximum, which can only be properly detected inside the vacuum chamber with a high-vacuum.