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Homework Help: The Conservation Laws - Particle Physics

  1. May 7, 2015 #1
    1. The problem statement, all variables and given/known data
    Screen Shot 2015-05-07 at 12.32.15.png
    Figure 1:
    Screen Shot 2015-05-07 at 12.31.53.png

    2. Relevant equations

    3. The attempt at a solution:

    P + P → K+ + K- + P + P

    Firstly, I just wanted to check that this is correct. I found the answer pretty quickly by googling it but have since spent a long while trying to understand it. I was hoping that someone might be able to affirm what I have learnt as I have read so much that I feel like I'm getting everything a bit confused now.

    As far as I'm aware everything in this collision is conserved apart from the isospin. Is this okay to do? and does this mean that I can now assume that this is an Electromagnetic Interaction?

    Secondly, Figure 1. gives the table we will be given in our upcoming exam.

    I was wondering what a few of the table headings are supposed to denote.

    In the quark table:
    I assume J = spin
    I3 = Isospin
    then what does I mean?

    and then again in the Hadron table:
    J = spin?
    I = Isospin?
  2. jcsd
  3. May 7, 2015 #2


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    Staff: Mentor

    Where do you see a change of isospin and how would that be relevant?
    The reaction is possible via the electromagnetic interaction, but the electromagnetic interaction is weak. There is another interaction that will dominate that reaction.

    Isospin is I, the parameter I3 is its component in "z"-direction.
  4. May 7, 2015 #3
    Thanks for your reply mfb,

    Think this is where i was getting confused.

    If the collision is: P + P → K+ + K- + P + P

    Then the conservation laws for the isospin aren't conserved?

    Following the order of the collision above the isospin would be: 1/2 + 1/2 → 1/2 + 1/2 + 1/2 + 1/2, 1 ≠ 2 (according to the table above)

    And I believe I read somewhere that if the isospin isn't conserved then it is a electromagnetic interaction.
  5. May 7, 2015 #4
    Forgot to say, I now see that kaon pair production must be a product of the strong force. Just trying to understand how and when I need to worry about the isospin. Or can there be two types of interaction happening simultaneously?
  6. May 7, 2015 #5


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    Staff: Mentor

    You cannot add isospin like that. "I" is the magnitude of a vector, those don't add linearly.
    That does not make sense.
    Not at all, if you take care of the number of up- and down-quarks in the same way you do it for the other types.
    It is possible to have more than one interaction type in the same process, yes.
  7. May 10, 2015 #6
    Thank you mfb, think I am there now.
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