Higgs Hunters Talk

Spotter's Guide: "backwards" tracks?

  • vrooje by vrooje

    The spotter's guide sometimes notes tracks that go "backwards" -- but I don't really understand what that means as there's no direction indicated on the images. Does this just mean the lines appear on both sides of the vertex, e.g. 2 lines make an X instead of a V?


  • DZM by DZM admin

    I personally interpreted "backwards" as meaning "away from the direction in which the majority of the lines are traveling from the vertex." Does that seem right? So, yes, more like an X than a V...


  • andy.haas by andy.haas scientist

    Yes, backwards means that the tracks continue "backwards" from the displaced vertex towards the center of the detector. This is an artifact of how the tracks are drawn, and does not indicate the truth path of the particles, if they really came from the vertex.


  • alanbarr by alanbarr scientist

    So in this image, for the collection of tracks a little below the center, the number of tracks is 5 (or perhaps 6?) We don't want to count each line twice - which we would be doing if we also added the stubs pointing back towards the middle.


  • jokergirl by jokergirl moderator

    I had problems understanding this section as well. "Backwards" does not really indicate anything in this context when you have never seen the picture before. You might want to work a little bit on your explanation then.

    So "backwards" means that instead of "starting" in the center point of the vertex a track continues on through the center? Makes a little more sense now, thanks!



  • vrooje by vrooje in response to alanbarr's comment.

    Ah, okay, it's for the count -- got it.

    I think it would probably help to just update the spotter's guide text so that the backward tracks tab says something short but clarifying at the start, like "Particles travel outward from the center of the detector", which does give it a direction so that backwards makes sense.



    Am I right in my understand the 'backwards' part is merely an artifact, if indeed the vertex is real?
    A related question: if the majority (or even all) of the trajectories diverge off-center, yet seem to originate from the center, would this most likely be an #ocv with a false extrapolation towards the center? Or a true origin from the center with a gradual effect of different charges causing particles to diverge?