ist it possible to detect particles by a trace or with event_touch or something like that?

Take a look at AUM 100, I've made an example of flamethrower via particles. They can detect objects and decrease their health. I hope it will help you, good luck.

nice example,
but i meant how to detect a particle itself

don't use a particle, use sprites instead...
particles can't have collision

I guess you cant detect particles themselfs, but tell us what you are trying to archive, maybe we could find a workaround for your situation

i create some particles and wanna select them with the mouse
like drag and drop
the solution i find for now is to use the distance of the
particle pos.x and the hit.x of a trace

now i calculate wich particle is the closest to the hit.x
with vec_dist, works for now but primitive a bit

hm.. why dont you use sprites instead of particles then? take a look at the samples folder, there should be example that creates same effect with particles and sprites, I guess it will help you