I want to know

how they know about neutrinos....you know those itsy-bitsy-teeny-weeny thingies that are smaller than atoms?
We used to think atoms were small. I used to wonder how they had found out about atoms. How can you know about something if you cannot see it? It was one of those things I wanted to know about when I was a child.
Do not mistake me. I had no desire to be a white-coated scientist in a laboratory. I have never wanted to do that. When I was at school "nature science" (as we called it) was so badly taught I was bored by it. I never enjoyed it. I grew up liking nature but not wanting to know about it in the sort of intimate detail that scientists needs. I know things of course. I am lucky enough to know where to find more information when I need it. Someone showed me a shawl pin made out of a piece of dark reddish timber yesterday. She did not know what it was. My father still works with wood. I have seen many pieces of timber in my life. I looked at the timber. I felt the weight of it in proportion to the size. I thought it was jarrah. My father confirmed it. Now I know, I know that - or do I?
I suppose experience told me that but I could see the colour. I could feel it. I do not think they can see neutrinos or that neutrinos are a particular, if any, colour. So, how do they know?
Oh yes, I know about CERN. I know about the big tunnel. I know that it is all costing billions of dollars for a small group of humans to try and satisfy their (and perhaps our) curiosity. I know that it is supposed to have potential applications of all sorts. All that is fine - but how do they know?
Einstein thought he knew. He wrote "that equation" and for around one hundred years it has been accepted as being right. Without Einstein - or someone like him - there would be no CERN.
But how do they know they know now? Is that why they are being cautious?