Muons and quarks in puzzeling way.
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DiNapoli
This if i payed enough attention this is an event like where 2 quarks appear a bottomquark and a anti-bottomquark and that a bottomquark can take a muon in it's decay as seen at aprox. 10 o'clock in this image. (a Z(->mumu) + bottom quark jets event as @andy.haas describes it). But in this image AHH0000pyo it's kind of puzzeling to me because it looks like both quarks seem to have a muon in their decay because they are very close to eachother as seem at 10 and 5 o'clock. And there is also a electron or photon in the picture at 4 o'clock in the muondetector. So if it's not to complex can anyone explain this a bit to me?
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markbakovic
If indeed they are bottom quarks (jets are not easy to analyse, the blue indicators should be read as "possible bottom quark jet") they may or may not be one bottom and one antibottom, and if they are, they may or may not be a pair coming from the same particle.
(that said, looking at some of the angles, depending on where those markers are in the z axis (which we can't see), they might very well be exactly as you describe a b and bbar, and even from the same particle. if so the "diametric" relationship of the two jets would suggest a heavy parent particle, which is interesting)
So given all of that, there is no reason both quarks shouldn't include muons in their decays. Remember that heavy quarks nearly always decay into "jets" of many particles, some of which may further decay. Muons in the resulting spray are by no means rare, but often they don't end up with enough momentum to get tagged by the computer (because much heavier hadrons get produced as well, which then decay themselves, in many cases "diluting" the momentum among many particles further). However if the jet has more leptons in it (a lot of which are quite stable, and so retain their momentum) then the chances are good that a muon will retain enough momentum to pass the event filter and get tagged/"green lined" in these images.
As for the photon, it could be related to the very-transverse muon at 3:00 and the two sets of deposits in the hadron calorimeter nearby, depending again on the z coordinates of each. There are particles which decay to pions and photons, and others to pions and muons (and intermediate hadrons which could survive that far too) etc. but with no more to go on than the image (z displacements I've mentioned, but also are the hadrons charged and low momentum, thus filtered out, or neutrally charged and thus unseen by the inner detector? we have no way to tell etc.) all we can do is speculate.
That's really all we can do anyway, but in the case of the photon even more so 😃
If Dr. Andy (or Prof. Peter for that matter) see this they might be inclined to weigh in with some percentages of leptonic b-jets and branching ratios of b/bbar particle decays given the Z ->mumu filter etc. as these sort of background processes are factored into their filtering of the events we see.
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DiNapoli
I'm reading this now I have to catch up due to eastern 😉 thnx Markbakovic!
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andy.haas
scientist
Another neat event from DiNapoli!
Here's what I see: two b-jets (one of which gives a significant energy muon in green, at 5 o'clock). A second muon at 3 o'clock which is isolated (no nearby other tracks or significant calorimeter energy). A moderate energy photon (or possibly electron whose track was lost). Some moderate MET.
If it is an electron whose track was lost, this is a perfect signature of ttbar -> WWbb -> e mu b b + MET.
If it's really a photon, then it looks to me like W+bb with W-> mu nu, and the muon radiates a photon. (Accelerated charge radiates light!).Which of the two scenarios is more likely is hard to say without a detailed simulation of the event selection and detector response and reconstruction.
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DiNapoli
Haha this makes my day lol 😃.
I'm on the net and found the "heynman diagrams" I didn't knew of these and they are quite handy and I'm trying to figure out what you all mean by those signatures.
But one thing I can't actually find on the net; what does moderate MET stand for? (Muon energy deposit (then the yellow blocks in the red calorimeter close to the muon are something like jets?), or Inverse momentum transfer?)
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markbakovic
MET is shorthand for "Missing Energy, Transverse", also written differently in print/journal articles with more formatting and font options available. It's the imbalance in the transverse momentum (ie momentum with x or y components in addition to the z component which points along the beamline). The particle beams enter the collision with next to no transverse momentum, so that "net zero" has to be conserved. It often isn't according to what is detected (ie all the transverse momenta registered add up to some x and y components other than zero, so there must be some measurement error, or some momentum in particles that weren't detected which flew out the other side.
Neutrinos don't interact with any part of the ATLAS detector so the MET is the only indication that some might have been produced. Again it's "possibilities": low MET could just be measurement error, moderate MET could be few (or even just one) neutrino(s), high MET might be multiple neutrinos.
If it is ttbar that's quite something: top quarks are hard to make!
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DiNapoli
Oke thanx for explaining the MET term it's clear to me now.
Yes I've red on the net that top-quarks are really heavy particles, heavy as gold particles!
I've discovered the feynman diagrams by the way they are really cool and helpfull.Just one little question(s) though; what does 'bar' stand for in 'ttbar' , resonance/oscilation or something?
And tt stands for top quark-top quark, but shouldn't it be top quark-anti-top quark? they need to have opposite charge if I'm correct so this Is why I ask.Posted
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peterwatkins
scientist
in response to DiNapoli's comment.
The bar in ttbar is an abbreviation for top quark-anti-top quark pair.
We use a bar over a particle name to represent the antiparticle.Posted
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DiNapoli
Oh oke I see, so you replace the bar with letters. And that immediatly answers my top quark/anti-top quark question 😉
Thank you very much.Posted