What is the smallest particle which we know exists, i.e. not theoretical

 

For me, the smallest particle is a quark, that i know.

You're going to have to define what you mean by small first. Quarks are fundemental particles though, and have been detected I think.

I thought you couldn't actually detect an individual quark (or was that observe) due too the confinement property of a quark?

Don't ask, me, i know quarks exist, but not much else

I thought you couldn't actually detect an individual quark (or was that observe) due too the confinement property of a quark?

 

Depends on how you define the word detect... There is significant evidence from particle accelerators for their existence. I don't think they've ever been seen individually though, but I'm not a particle physicist...

 

But depending on your use of the word small you could say electrons or muons are smaller.

 

And neutrinos are nearly definitely smaller...

To me, it still blows my mind that we've been able to visually see individual atoms thanks to electron microscopy. No matter how many times I see it, I'm still blown away.