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A Track Reco in the Inner Detector of ATLAS

  1. Apr 27, 2016 #1


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    I was reading about track reconstruction. So, I read about the "inside-out" and "outside-in" strategy for track reco. However both those strategies utilize information coming from the InDet parts... I know though, that the Muon Chambers are also used for the track reconstruction in ATLAS. How is the connection done? is it a "muon reco" or let's say "high-pt particles reco" thing alone [by expanding the idea of trajectory extrapolation]?

    Also I have a question on the part of inside-out strategy... In the following paragraph I explain how I understand the strategy up to the point that confuses me, the question is in the next:
    The main points of this strategy is to look for hits within the Pixel Detector and the SemiConductor Tracker (SCT). You test tracks which match those hits and the ones with the highest score are taken as the track seeds (grouping the hits together into tracks). Then you use those tracks to test them again, trying to clear out fakes or incomplete. You remain with the silicon tracks. Then you use their last hit in the outer part of the SCT to extrapolate their trajectory through the Transition Radiation Tracker (TRT). Any measurements in the TRT that are within some radius around that path (accounting for drifting) are assigned to the silicon track.

    Then the new extended tracks are re-fitted and are compared to the silicon ones using the track scoring mechanism. In case the silicon tracks score is higher than the extended version, the silicon track is kept.
    Why is the silicon track kept over the extended one? I mean wouldn't it make more sense to say that "well my extension did not work out well, so there must be something wrong with my track itself" and just throw away the whole track? Otherwise it seems like we go with the idea that TRT measurements were not as reliable as the PixDet and SCT, it gave us a worse result so we keep the "good" one.
    Any idea? thanks.

    (http://www.nikhef.nl/pub/services/biblio/theses_pdf/thesis_M_Limper.pdf p107)
    Last edited: Apr 27, 2016
  2. jcsd
  3. Apr 27, 2016 #2


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    The tracks from the inner detector and from the muon detector can be matched to form a combined track. You can find more details in the corresponding publications. This is not ATLAS-specific, every detector does it like that if there is significant material, flight distance, magnetic field or something else in between tracking elements.

    Concerning the TRT: I don't know, but I can imagine that the TRT is not as reliable as the silicon detectors. In addition, for electrons you always have the issue of bremsstrahlung, where your track direction can change suddenly.
  4. Apr 27, 2016 #3

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    There's nothing wrong with the TRT. If you have a good silicon track, you have a particle. If it doesn't extend into the TRT, it means the particle isn't there any more - perhaps it decayed, or was absorbed, or had a hard brehm, or otherwise interacted with the material in the detector. If this is the case, adding a stray hit or two from the TRT will make the track worse, not better.
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