Is it something special or a normal appearance?
by Whoandwhatitis moderator
The purple circle is a common occurrence. It's left over from the processing that the computers have done to generate the image. More on this in the FAQ.
However, this image shows two bottom quark candidates (blue bars outside the last detector - the muon chamber), which is quite rare in my experience. Since they don't have paths leading to them, I can only guess that one is a bottom quark and the other is an anti-bottom. This is exciting in this project because the Higgs boson most frequently decays to a bottom and anti-bottom pair.
This is how I see it based on the Slice view and Normal view, because the bottom quark is right in line with that purple circle in the Slice view, and it seems likely that the other one is likely below the beam line just as the pair of muons (green lines).
Nice find, @k.till1484. I'm going to save this one!