Lots of Energy, but no particles
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by
germandan
I see a lot of energy at the bottom of the image but no particles that generated it. Does the system deliberately leave out some of the particles or is indeed something strange here?
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by
alanbarr
scientist
There are two possible explanations here.
First, it's true that the lowest energy tracks are deliberately left out of the images, to make it easier to identify the higher-energy, more interesting tracks we expect from off-center vertices. The low-energy tracks curl up more in the magnetic field. You might see some evidence for them in the grey hit-maps in the background, but we don't flag them with lines.
Second, only electrically-charged particles (like protons or electrons) leave tracks. Electrically neutral particles, like neutrons and photons, do not leave any tracks at all. As you say, the object at the bottom of this image has left lots of energy in the electromagnetic calorimeter layer (green), but has not track. This is the characteristic signature of a photon (i.e. particle of light).
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Can we mark this energy bursts to Something Weird?
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germandan
That makes sense, thanks for the explanation Alan!
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andy.haas
scientist
Also, we are only showing the tracks that come no closer than 1mm (in the normal view) to the proton collision. This is ~95% of tracks, and makes it MUCH easier to spot displaced vertices, from displaced tracks.
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Whoandwhatitis
moderator
in response to andy.haas's comment.
Would this explain why I might see one or two wide red signal in different positions on the the muon detector, but no line leading up to them? That is, the particles originated from less than 1 mm from the proton collision.
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andy.haas
scientist
Possibly (more than 1mm).
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