Higgs Hunters Talk

4 green lines: Four muons?

  • Whoandwhatitis by Whoandwhatitis moderator

    Just opening up a new discussion in response, @ya_78.

    In this one, I count six green lines in total. The sixth one is very difficult to see in Normal view, but if you select Zoom or Slice view, you can distinguish them pretty readily.

    4 green lines. That means four muons?

    Yes, these are likely muons (or something mistakenly tagged as muons).

    From the FAQ:

    Q: Why are some lines a different colour? - A: The only colours of
    consequence are green (the muons coming from the center) and the red
    dashed line, which is not a track at all. Other than that, the colours
    don't mean anything specific, but are markers for that the computer
    thinks the lines come from the same vertex. (Read more about the
    colours and dots on the detectors below!)

    I see three red rectangles in the muon detector area (thin, blue circular outer ring in Normal view), all of three different sizes.

    You might also find the discussion "Missing trails, tracks, trajectories etc of muons." interesting. This is the discussion that may have prompted the "missingmuon" hashtag. We see one example at around 235° in the Normal view of the subject AHH00009bp.


  • Will.K by Will.K scientist

    This is an image with a lot going on! Thanks for flagging it. In three parts:

    1. I think this is an unfortunate case where one of the "from the same computer-identified vertex" colours is green, and so the associated tracks look like muons. In the Normal view, it is the two tracks that extend all the way out, and end near red rectangles, that are the muons. The more curved tracks (i.e. lower momentum particles) that don't reach the calorimeters (the green and red shaded circular areas towards the outside of ATLAS) are not identified as muons - in fact one of them seems to be identified as an electron (green rectangle at about 1 o'clock).

    2. Regarding the 'missing muon': this is I think due to slightly different conditions being required for a track to be drawn on the image and for a muon to be marked around the outside.

    3. As well as being made confusing by point 1, the slice view is further complicated by the fact that the tracks straddle the 'break point' in the projection - all points in the top left of the Normal and Zoom views end up on the top of the Slice view, and all points in the bottom right go to the bottom. If you look carefully, you can see the red tracks are in the top half of the Slice and the orange ones in the bottom half, while in the Normal and Zoom they are close together. Normally this isn't such a problem, but here the other muon and baby Higgs have conspired to lie ~ on top of this 'reflection' in the R-Z plane, making for a messy image. Luckily the break point is in the same place for all images (about 40 degrees from the horizontal) so I know to look closely when there is activity in this region.