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Higgs boson lifetime and decay length?

  1. Jan 13, 2012 #1
    I am trying to figure out how fast the Higgs decays and how far it travels in a detector at the LHC. Figure 2.5 in http://www.hep.lu.se/atlas/thesis/egede/thesis-node14.html gives decay widths of the Higgs as a function of its mass.

    For a Higgs of 125 GeV, it is 0.002 GeV. Using the Heisenberg Uncertainty eq. lifetime*decay width = h-bar/2, I find lifetime = 1 zeptosecond. Is this correct? What kind of assumptions can I make about its speed so that I could calculate distance travelled?
  2. jcsd
  3. Jan 13, 2012 #2


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    An easy way is to use the value of Planck's constant in the form ħc ≈ 200 MeV-f. This says that a particle with a width of 200 MeV will travel about a fermi before it decays. More generally the distance traveled is ħc/Γ. So if the width of the Higgs boson is, as this guy claims, 2 MeV, the distance it travels will be about 100 fermis. A highly energetic Higgs will travel somewhat farther than this due to time dilation.
  4. Jan 13, 2012 #3
    Dear Bill_K,

    thanks for the input. By using c in the equation, you are assuming that the Higgs travels at (close to) c, are you not? If this is the case, then time dilation will be a significant effect.

  5. Jan 13, 2012 #4
    If the resonance peak is centred on the Higgs rest mass, and Γ << mH, then it will be slow.

    Its momentum will be of the order

    pH ≈ Γ / c

    so, by the uncertainty principle, this implies an uncertainty in its position of

    Δx > ħ / pH = ħc / Γ

    which gives an indication of how far it will travel.
  6. Jan 13, 2012 #5

    Vanadium 50

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    I think you will find that if it travels for zeptoseconds that any correction of a factor of a few does not make any practical difference.
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