When you look for it, you either find a neutron that has not decayed yet, or you find the decay products.
The quoted decay time is just the average time. A free neutron might decay after 1 millisecond or after 5 hours.
Like for any other decay process, it is unpredictable when an individual neutron will decay. Nevertheless the decay probability in a time interval is predictable so if you start with a large number of free neutrons, you can predict very accurately how many will remain after 1 minute or after 10 minutes or after an hour, because the number will decrease exponentially with a known time constant, which was measured more precisely in this new experiment.
In my opinion the word 'virtual' doesn't help as it's a catch-all word for when we've no clearer description. That's certainly not a criticism of you for using it, it's just a bit vague or general when we also apply the name in connection with Zero Point Energy/Quantum Vacuum, Casimir and static electric/magnetic fields etc. My point is that a 'virtual W' is significantly different to the others I've mentioned.
That said, you'll note in my reply to adrian_b that I'm no angel in such matters either in that I've postulated somewhat by repurposing a Feynman diagram as a graph. But then, Wiki led the way by providing the axis!
Is the total time taken for a neutron to fully complete its decay longer but still comparable to the time taken for the W- boson to decay into an electron and antineutrino or is the latter's decay time much, much shorter than the overall process? That is, is the following statement true or otherwise?
[time (total) for n0 → (p+) + (e-) + (-ve)] >> [time W- → (e-) + (-ve)]
...and if so, then do we know by how much; if not then what is it? Alternatively, if the Feynman diagram for neutron beta decay shown in the following link were to actual scale then what would the scale on the vertical (time) axis be? https://en.wikipedia.org/wiki/Free_neutron_decay
I'm not really trying to be deliberately pedantic or dispute orthodoxy here but my question was in response to these and similar recent stories:
https://scitechdaily.com/zeptoseconds-new-world-record-in-sh...
https://www.quantamagazine.org/quantum-tunnel-shows-particle...
If the info therein is all or in part factual, or if similar measurement methodologies were applicable to other particles, then the ballgame may change, hence the initial reason for my question (similarly so for my first/initial post).
The second (Quanta magazine) link was the subject of a HN story going on about a year ago and it generated many comments (they resolved nothing but many were interesting nonetheless); unfortunately the time for comments was up before discussion had finished (my last, rather prolix comment was still in draft and missed the deadline). In my opinion, controversial topics like this should sometimes be left open to give one time to dwell upon them.
In hindsight, it seems the techniques mentioned in those links to measure a particle's time are unlikely to be applicable or adaptable here. That then begs the question about how did we initially determine that the W- boson's decay is much faster than the overall process.
