Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Flavour Content of Particles

  1. Apr 23, 2010 #1
    1. The problem statement, all variables and given/known data

    To calculate the flavour content of these particles:

    [tex]\pi^{-},K^{+},\hat{B}^{0},\pi^{0},\hat{\pi}^{0}[/tex]

    *Note that the [tex]\hat{}[/tex] notation should actually be a flat line, which I believe denotes the antiparticle, but I don't know how to do this in latex code. If anyone can let me know for future reference that would be great*

    2. Relevant equations

    These are the hints given in the question:

    • Pions are the lightest Mesons
    • Kaons have Strangeness of [itex]\pm 1[/itex]
    • B-Particles have Bottomness of [itex]\pm 1[/itex]
    3. The attempt at a solution

    I'm not sure how to do this.

    I know that:

    Quarks have flavours of u,d,c,s,t,b. These are abbreviations from Up, Down, Charm, Strange, Top, Bottom. The respective charges are [itex]\frac{2}{3},\frac{1}{3},\frac{2}{3},\frac{1}{3},\frac{2}{3},\frac{1}{3}[/itex]

    Leptons have flavours of [itex]v_{e},e,v_{\mu},\mu,v_{\tau},\tau[/itex] and these decrease from lightest to heaviest in this order listed. The respective charges are 0,-1,0,-1,0,-1

    Each of the objects must be charge neutral and also colour neutral.

    Hence can have either 3 quarks (known as Baryons) or a quark-antiquark pair (known as Mesons). Both Baryons and Mesons are types of Hadrons.

    So I've got a bit of the theory, but unsure how to put this together in regards to identifying the flavour content of the particles. A little bit of help and advice would be much appreciated. :smile:
     
  2. jcsd
  3. Apr 23, 2010 #2
  4. Apr 23, 2010 #3
    Thanks for the link.

    So for example on that link, the pion [itex]\pi^{+}[/itex] is listed as having quark content (which is the 'flavour content' right?) of [itex]u \ihat{d}[/itex]. I need it's listed antiparticle [itex]\pi^{-}[/itex] so for this it's flavour content will be the opposite, i.e. [itex]\hat{u}d[/itex]?
     
  5. Apr 23, 2010 #4
    Yes, the antiparticle consists of the antiparticles of all the quarks that make it up.
     
  6. Apr 23, 2010 #5
    OK.

    I'm not sure how to explain the results for [itex]\pi^{0}[/itex] and [itex]\hat{\pi}^{0}[/itex], need to have a little explaination not just state the values and the theory for these two is a bit more complicated it seems just from looking at their flavour contents.
     
  7. Apr 23, 2010 #6
    Well for the neutral pion you need 0 charge and lightest possible quarks. For more complicated reasons it is a superposition of u(-u) and d(-d)
     
  8. Apr 23, 2010 #7
    You can probably get away with just saying u(-u) for the neutral pion. If it is an introductory course.
     
  9. Apr 23, 2010 #8
    Yeah it's an introductory course so it's not too in depth particle physics.

    So basically for that one its flavour is (u,-u) because it's charge is 0 and flavour must be neutral, right.
     
  10. Apr 23, 2010 #9
    That and it is the lightest possible combination you can make.
     
  11. Apr 24, 2010 #10
    [itex]K^{+}=u\hat{s}[/itex] because kaons have strangeness of [itex]\pm1[/itex], and since the charge of [itex]s[/itex] is [itex]\frac{2}{3}[/itex] then can balance this with [itex]u[/itex]

    .. is this correct? This is what wiki lists it as but I'm slightly confused with the theory and understanding behind the answer.

    Alternatively, is it rather that in regards to charge [itex]s=-\frac{1}{3}[/itex] therefore [itex]\hat{s}=\frac{1}{3}[/itex] which combined with [itex]u=\frac{2}{3}[/itex] gives a charge of [itex]0[/itex]? Unsure if I can just reverse the signs when going between particle and antiparticle.

    ..but why is it [itex]u[/itex] not [itex]c[/itex] or [itex]t[/itex]? Since these all have the same charge of [itex]+\frac{2}{3}[/itex]. And the same for pairing it with [itex]\hat{s}[/itex] not [itex]\hat{d}[/itex] or [itex]\hat{b}[/itex]

    I'm sure there's a simple explaination as to why [itex]u[/itex] and [itex]\hat{s}[/itex] are chosen? I can only think becuase kaons have strangeness so use [itex]s[/itex].

    In regards to [itex]\hat{B}^{0}[/itex] in a similar way use [itex]\hat{b}[/itex] but again why is this? And why choose to pair it with [itex]\hat{d}[/itex]?
     
  12. Apr 24, 2010 #11
    The [tex]K^+[/tex] does not have +/-1 strangeness. It has only +1 strangeness. You were only told that Kaons in general have +/-1 strangeness. But to satisfy the +1 charge, you need an anti-strange quark which gives you strangeness +1. Also the charge of an anti-strange is +1/3 and not +2/3.

    1/3+2/3 = +1 and not 0

    You weren't told it had charm or topness.

    It doesn't have charm or topness so you chose "u". Also you were told it had strangeness so it must have a strange quark. Then all you do is conserve charge.

    Up and down are the only ones not given crazy quantum number names. You know it must have a bottom quark, so to conserve charge you need a down quark. Just make sure one of the quarks is an antiquark. Unfortunately, I don't have a reason for choosing the bottom quark as an anti-quark. It might just be naming convention.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook