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Homework Help: Branching ratio of particle question

  1. Jun 10, 2014 #1
    1. The problem statement, all variables and given/known data
    The J/Ψ has mass 3097 MeV, width 87 keV and equal branching ratios of 6%
    to e+e− and µ+µ− final states. What would you expect for these branching
    ratios if the J/Ψ decayed only electromagnetically? What does this tell you
    about the “strength” of the strong interaction in this decay?

    2. Relevant equations
    Branching function = Width/Sum of all Widths

    Don't know whether this will be useful or not but:

    Lifetime of u = 2.2*10-6
    Mass of u = 106MeV/c2
    3. The attempt at a solution

    I don't really know what to do, I don't understand branching functions that well and I'm not even sure if the question requires me to calculate anything, i'm confused.

    I know that strong forces dominate and that the average lifetime for strong interactions is ~10-24seconds whilst EM ~ 10-18.

    This isn't homework really, this is just revision for an examination I have tomorrow. If somebody could just explain this briefly, that would help immensely.
  2. jcsd
  3. Jun 10, 2014 #2


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    Not sure (hopefully someone else jumps in if I am wrong), but if hadrons are excluded, then only 50/50 e+e- / mu+/mu- remains, isn't it ?

    Get some rest, much better than last-minute worries for an examination :approve:!

    12% leptons vs 88% hadrons is already very high because hadronic decay is heavily suppressed. See wikipedia and particle data group page 2 and this link which illustrates this OZI suppression.
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