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Measuring the spin of a Higgs Boson.

  1. Dec 3, 2008 #1
    Premature, I am well aware. However, I was given an assignment to write an experimental procedure for measuring the spin of the Higgs Boson. I've already finished the paper so this isn't homework, but I am curious as to the motivations of my Professor.

    It is my understanding that the Higgs Boson must have a spin of 0 so as to conform to the theory that the Higgs field is scalar, which is something on which the entire higgs-field theory rests. Finding only (a) particle(s) in the range of the Higgs' mass that did not have a spin 0 would imply that it is, in fact, not the predicted Higgs Boson, debunking the theory. Would it be more appropriate just to design an experiment to measure the spin of particles within the bounds of the Higgs' mass? Or is the goal likely to be to corroborate the idea that we will have observed the Higgs?

    The theory on which my experimental procedure relies (for any who are interested/have constructive(corrective) criticism)

    The Higgs is large (a minimum mass of 114 GeV, a predicted mass of 129 GeV) which indicates that it should have a very short life before it decays. So, while the quick decay time may prevent the possibility of measuring the spin of the Higgs directly (Stern-Gerlach, 0 spin would imply that the beam should go straight through the B-field), there is the possibility of using a hermetic detector to identify the decay products and sum their angular momentums. If that sum is zero, then we have possibly observed the predicted Higgs particle.

    Possible difficulties I am aware of: LHC can only produce a Higgs Boson once every couple of hours. I understated (Just didn't discuss here) the difficulties of identifying the decay products.

    I suppose this brings me to a last question. Is anyone aware of any promising duration predictions for the Higgs Boson?
  2. jcsd
  3. Dec 3, 2008 #2


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    I don't even know if LHC CAN measure the spin of the higgs boson to a great certainty since it is not created at rest in lab frame (not a head on production due to quark and gluon distribution functions of the HEAD ON protons). Therefor one needs a lepton-lepton collider for such fine tuning measurements.

    Well in reality, the situation to measure spin is even harder since depending on what mass Higgs has, certain decay channels are more probable and possible etc. The "Golden Channel" is H-> ZZ where each Z decays into a muon.antimuon pair, is the cleanest one, has the smallest background.

    Also your detector is nothing like the detectors at LHC, one measure the angular distrubution of the particles and compare with theoretical obtained ones. You don't look at one event and say "hey this event came from a spin 1/2 particle".

    There should be lot of resources for you at CERN website.
  4. Dec 3, 2008 #3


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    Don't all/many of the Higgs production modes have decay products equivalent to other scalar production modes?

    My understanding is that the mass is all important. If I remember correctly the dominant decay mode for a ~120 GeV Higgs is 2 photons which has a massive background signature, which would take years to get statistics. (correct me if I'm wrong).
  5. Dec 3, 2008 #4
    As malawi_glenn mentioned, if you collect enough statistics (that is, more than just to measure the mass) you can decompose the angular decay distribution. If it's uniform in solid angle, it's a scalar.
  6. Dec 3, 2008 #5


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    And scalar = spin 0 particle, transforms as a scalar under rotation.
  7. Dec 3, 2008 #6
    Almost all particle physics experiments will take years of data compilation and analysis to get any definitive results. It's kind of like trying to identify fish in the dark by reaching into a fish tank filled with different species. You have to start giving arbitrary names to familiar forms and keep finding distinguishing attributes that you can use to form groups. And even then they have features that you may not be aware of.
    Last edited: Dec 3, 2008
  8. Dec 3, 2008 #7
    Thanks for the clarifactions guys!
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