Higgs Hunters Talk

What are we seeing?

  • jokergirl by jokergirl moderator

    I would like to know a little more about how the pictures we are seeing are generated, in order to better understand what I am classifying. If I understand this correctly from the "backwards" discussion, the "lines" are not actually images of anything but tracks made by a computer?
    On the other hand, how can a computer then "miss" the white lines, and the human eye be better at spotting them - I could probably manage to make an image analysis program that could point them out quite easily in the pictures I have seen so far. What are those images really?

    I would also like to know more about the "side view" - I can't really figure out what/where the center is supposed to be in those images, and what the line of colourful dots and circles we sometimes see in the middle of the image means.

    Can you add a little more background somewhere on the page? The tutorial as it is is quite confusing, and I'm talking as a GZ/citizen science veteran 😃

    😉

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  • DZM by DZM admin

    Good questions @jokergirl; thanks for asking!

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  • andy.haas by andy.haas scientist

    The lines (curved lines) are paths reconstructed by the computer by joining the hits together (the little dots you see all over the tracker). The white lines could not be matched by the computer with a vertex. This is the hard part.
    The center (in the vertical direction) of the slice view is the beamline where the protons are traveling. Other proton collisions take place along the beamline and these are found as vertices by the computer and drawn. We've suppressed drawing the tracks which are coming from the beamline in order to make your job of finding displaced vertices easier. (There are hundreds in some events!)
    We'll continue to fill in more detailed info on the pages through the talk forums and blogs in the near future.
    Thanks for the great questions!

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  • jokergirl by jokergirl moderator

    Aaah! That makes a lot more sense already. Thanks for the explanations!

    Looking forward to reading more when you get around to it, but this already helps a lot in classifying what I see right now...

    😉

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  • jokergirl by jokergirl moderator

    To summarise:

    • The lines are computer generated (am I right in thinking that the grey areas have sensors and the computer interpolates the curves between those lines?) and then the computer tries to make a curve according to a known function out of it (this is what makes coloured curves). White means that the computer does not know what to make of it, and our eyes are required to find the actual connections between curves.
    • "Backwards" means that the interpolation overshot the origin point of the vertex due to limitations in this interpolation (so in order to find vertices, just look for an origin point where two or more lines cross and ignore lines overshooting towards the center)
    • In the slice view, the center is the vertical center of the image aka the line around which the grey areas are mirrored (in the other views, the center is the center point both horizontally and vertically).
    • Coloured circles and dots can be safely ignored. ETA: As can "single" off-center white lines, or line crossings that are obviously not a vertex but simply superposition in 3d-space.

    Anything I forgot so far?

    😉

    ETA: Taken from another thread (quote from andy.haas):

    "What could be weird? Lots of tracks in one tight bunch, or coming out at weird angles but not forming a vertex, or a big amount of tracks on one side but the other side, or lots of energy in the calorimeter (the red/green areas beyond the tracker), or things in the muon system (the outermost detector)... what ever looks weird to you!"

    (PS: I'd really like to know more about the calorimeter and what the white fields and yellow squares in the red and green bars mean... also, what the line colours mean! So far I've gathered from discussions in tags that green means muons and a pair of white OCVs are a sign of down quarks decaying...)

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  • nblazer82 by nblazer82

    @jokergirl Thanks for asking all those questions that are running through my mind, too, when trying to classify or spot interesting things. As you, I'd really like to get some more information on what we're seeing here.

    Something else I've been wondering: how much do angles matter? When spotting a possible off-center vertex, I suppose there should be kind of an intended trajectory pointing back at the center, even if not visible, right? Or is it possible for vertices to split into completely random directions?

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  • alanbarr by alanbarr scientist

    As far as angles are concerned, if the #ocv is really caused by a new type of particle moving away from the center, we'd expect to find at least some of the decay-particle-tracks to also be moving away from the center. (This is the physics of "Conservation of momentum" in action!)

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  • nblazer82 by nblazer82

    @alanbarr Thank you, makes a lot of sense.

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  • Gers by Gers

    This post is great! Very good questions and answers.

    As @jokergirl and @nblazer82 point out, it is possible (and so much fun) to find many more interesting things if we have more information about what we are seeing in the images, and the different tools involved in the particle detection. I missed many weird things in the images I already classified because of not knowing about the calorimeters, for instance.

    Maybe those suggestions of weird things (by @andy.haas) could be added as new examples in the /classify page.

    Thanks!

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

    Any chance this is what you mean re a particle going the other way Image AHH0000fwf ?

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  • andy.haas by andy.haas scientist

    (PS: I'd really like to know more about the calorimeter and what the white fields and yellow squares in the red and green bars mean...

    The yellow areas in the red and green detectors (the hadronic and electromagnetic calorimeters, respectively) measure the amount of energy left in that spot by the particles going through (and/or stopping) there. They can measure neutral particles like neutrons, photons, etc., that the tracker can not see.

    also, what the line colours mean! So far I've gathered from discussions in tags that green means muons and a pair of white OCVs are a sign of down quarks decaying...)

    Yes, muons are drawn in green. (Sometimes there are other tracks that are also green, sorry. But the muons go farther, into the outermost muon detector, and have thick red lines at the end of them.) You may notice that there are at least 2 muons in almost every event you see. We've selected the events to have a Z boson decay to a pair of muons. This greatly enhances the chance that there's a Higgs boson decay in the same event!
    It's great that you're so interested in more about our detectors and particle physics - I agree it's exciting stuff. We can surely help you all find more info on ATLAS and the LHC online!

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  • Marcuandy1981 by Marcuandy1981

    I have a question. If the red means the muon's energy, what does the blue marks means in the outer circle?

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  • Marcuandy1981 by Marcuandy1981

    I observed that the blue markings usually appears in opposite to the red ones, so the blue marks are also energy, but from particles with opposite charge?

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  • andy.haas by andy.haas scientist in response to Marcuandy1981's comment.

    Good one! The blue lines in the outside indicate "jets" which are tagged as having likely come from the decay of a bottom quark. These quarks are fairly rare compared to the more common up/down or even strange/charm quarks, since they are much heavier (~5 GeV, one 25th of the Higgs mass). We identify them by looking for .... displaced vertices! The bottom quark goes ~3mm before it decays. They are thus a background to the kinds of ocv's you folks are looking for.
    The "jets" are collimated sets of hadrons (strongly interacting particles) and photons which hits the calorimeters. Their energies are measured there, and is plotted with these funny gray curved trapezoids.

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  • Mark_..._a_physicist_of_sorts by Mark_..._a_physicist_of_sorts

    Hi, I seem to remember going to a talk the day after the Higg's discovery was announced & hearing a guy form the ATLAS team talking of an excess in the number of di-photon decays (these di-photon decays provided evidence for it being a boson they had found as the spins added up correctly.) In his diagrams the yellow lines were photons. If the same colour scheme is being used, how is it we occasionally see yellow tracks curving, as if the particles were charged??

    In essence can we have a spotter's guide to colours? Pleeeeease???

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  • brownfox by brownfox

    I'm sure that they're not using the same scheme: photons, being uncharged, wouldn't show up in the inner detector (the grey bit) at all. There would just be a dump of energy in the calorimeters. Have a look at: http://talk.higgshunters.org/#/subjects/AHH0000654 and notice the yellow in the green calorimeter ring at about 3 o'clock and half-past 5. I think that's two photons.

    I don't think the colours in the images we see have any meaning beyond "these lines have been traced back to a common vertex by the computer".

    Cheers
    Steve (not really a physicist)

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  • andy.haas by andy.haas scientist

    Steve is right. Photons will be hard to see, given the info you have in these pictures.
    In fact, Steve, those two blobs in your event may be photons, but more likely they are jets of hadrons and photons. We're not drawing the tracks coming from the primary collision (only the ones from at least 0.5mm away), so you can't tell from what's shown. Not a bad guess though!

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  • jokergirl by jokergirl moderator in response to brownfox's comment.

    I don't think the colours in the images we see have any meaning beyond "these lines have been traced back to a common vertex by the computer".

    That is how I read it as well now. I have amended the FAQ to reflect that.

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  • peterwatkins by peterwatkins scientist

    The main focus of this search is finding two or more tracks starting at the same point which is displaced from the proton-proton collision point. This collision point is where the two green tracks (muons) meet. All these tracks (white or coloured) are reconstructed from signals in the tracking detectors which only detect charged particles. The tracks that point back very precisely to the collision point (except for the two muons) are not displayed to make it easier to look for the ocvs.
    The calorimeters (red and green regions) detect and absorb both charged and neutral particles and the yellow blocks in these regions represent energy deposited by both charged and neutral particles.

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  • undefined by undefined

    thank you for your post @peterwatkins

    Very helpful and interesting 😃

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