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

I About Quarks

  1. Dec 10, 2017 #1
    I understand there are three generations of quarks, which have the same charge but different mass. My question is, in a single generation how many different kinds of quarks are there. For example, in the first generation there are the up quark and down quark, each of which has an antiquark. So far, this is four different quarks in the first generation. Are there other properties in the first generation of quarks that would account for more first generation quarks? Thanks.
     
  2. jcsd
  3. Dec 10, 2017 #2

    dukwon

    User Avatar
    Science Advisor
    Gold Member

    Sure, you could also count the 3 different values of colour charge.
     
  4. Dec 10, 2017 #3
    So how many different first generation quarks does that give us?

    As I understand it, quarks interact with the electromagnetic force and with the Weak nuclear force. Does that mean each quark has an electromagnetic charge and Weak nuclear charge numbers?
     
  5. Dec 10, 2017 #4

    mfb

    User Avatar
    2017 Award

    Staff: Mentor

    It depends on how you want to count them. 2, 4, 6 and 12 are all somewhat justifiable answers.
    Yes, and you can look them up.
     
  6. Dec 10, 2017 #5
    I've tried to look it up, but those articles don't distinguish very well the case of a single generation.
     
  7. Dec 10, 2017 #6
    I find on Wikipedia,

    600px-Strong_force_charges.svg.png

    The black dots seem to be for gluons. The colored triagles seem to be for quarks. Is this just for a single generation of quarks?

    The diagram seems to indicate that the upsidedown triangles represent the anticolor charge of the rightsideup charge. Is this correct? If so, does the diagram indicate that whenever the color charge is reversed there is also a reversal of electric charge? Thanks.
     
    Last edited: Dec 10, 2017
  8. Dec 10, 2017 #7

    mathman

    User Avatar
    Science Advisor

    There are six basic different quarks: down, up, strange, charm, bottom, and top. Each has an antiquark. Also each comes in three colors (red, green, blue - labels which have nothing to do with color as such). You can count them anyway you want.

    Color charge and actual charge are not connected. up, charm, and top have charge +2/3, down, strange, and bottom have charge -1/3. All quarks may come in any color.
     
  9. Dec 10, 2017 #8
    OK Thanks. So I take it that the diagram in my previous post was for one particular quark, say the up quark, for example. So if I'm understanding you correctly, this means there are six possible ways to assign electric charge and color charge to the up quark. (+, - electric charge times red, green, blue, color charge). Is there an anti color charge? The wikipedia site I link to says there is an anti-red, anti-green, and anti-blue color charge as well. Is this right? Or is anti-red just the red charge with the opposite electric charge? I'm still a little confused.

    Reading the linked article, I read, "Antiquarks have the opposite charge to their corresponding quarks; up-type antiquarks have charges of − 2⁄3 e and down-type antiquarks have charges of + 1⁄3 e". This tells me that antiquarks differ from quarks by electric charge, e. I also read, "Every quark carries a color, while every antiquark carries an anticolor." which tells me that there is such a thing as anticolor, but that property changes with electric charge so that there are still only six possible ways to assign electric and color charge to, say, an up quark. Could someone please confirm this?

    Here's a question that may answer: do mesons have electrical charge. For mesons have a quark and antiquark. If this involve anticolor but not anti-electric charge, then perhaps that answers my question.

    Thanks.
     
    Last edited: Dec 10, 2017
  10. Dec 10, 2017 #9

    jtbell

    User Avatar

    Staff: Mentor

    Some do: ##\pi^+ = u \bar d##. Some don't: ##J/\Psi = c \bar c##.
     
  11. Dec 10, 2017 #10
    If there were no mesons with electrical charge, then I'd say that anticolor is the electrical negation of the color charge. But if there are mesons with electrical charge, I don't know that if I can say that an anticolor is the electrical negation of a color charge. Any help out there?
     
  12. Dec 11, 2017 #11
    So I think there is a correction for first generation quarks. They have either up or down flavor, +2/3e or -1/3e, and red, green, or blue color charge. So that means there are 2X2X3=12 different first generation quarks, right?
     
  13. Dec 11, 2017 #12

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    These are equivalent based on the Gell-Mann-Nishijima formula ##Q = Y/2 + T_3##. There is no up quark with charge -1/3.

    If you want to count degrees of freedom (and the argument can be made for this - I would therefore add 24 to the list of @mfb), then there are:
    • Quark-antiquark (2)
    • Spin/handedness (2)
    • Colour (3)
    • Up/down type (2)
    which in total would make 24 per generation.
     
  14. Dec 11, 2017 #13
    So maybe we can construct a table for first generation quarks only. Now that up or down is correlated with electric charge and color charge is correlated to electric charge, how many first generation quarks are there with just these quantum numbers?
     
  15. Dec 12, 2017 #14

    mathman

    User Avatar
    Science Advisor

    No! The up quark has a +2/3 charge and the down quark has a -1/3 charge. Both come in all 3 colors, so the total is 6.. If you add in the first generation anti-quarks, then you can get 12.
     
  16. Dec 12, 2017 #15

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    From a theoretical point of view, I would also count left- and right-handed separately (see #12). After all, the left- and right-handed components are parts of different SU(2) representations. There are many ways to count here, but for me the more natural one is to count degrees of freedom, of which there are 24 per generation. Before electroweak symmetry breaking you have
    • The SU(2) doublet and SU(3) triplet ##Q_L##. (6 Weyl fermions = 12 degrees of freedom)
    • The SU(2) singlet and SU(3) triplets ##u_R## and ##d_R##. (6 Weyl fermions = 12 degrees of freedom)
    Therefore, the total number of degrees of freedom among the quarks are 24.
     
  17. Dec 12, 2017 #16
    I understand that the quarks interact with the Weak force particles. Are all the quarks effected equally by all the Weak force particle, W+, W-, and Z0? Or does each Weak force particle interact differently with each quark? Thanks again for your help.
     
  18. Dec 12, 2017 #17

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    No. The weak force treats left- and right-handed particles differently. The couplings to the Z also depend on the charge of the particle and whether it is up or down type. The Ws couple (left-handed) up and down type quarks with a strength proportional to the elements of the CKM matrix.
     
  19. Dec 13, 2017 #18
    Do quarks rotate into each other like neutrinos?

    Do quarks decay into only Weak particles, say, a W- and Z0?
     
  20. Dec 13, 2017 #18

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    Are you referring to neutrino oscillations or neutrino mixing? They are related but different things. Neutrino mixing (or more accurately, lepton mixing) is necessary for neutrino oscillations to occur and quarks mix in much the same way. However, the big difference is that typically the neutrino mass states are quite degenerate in mass and so you will typically produce a linear combination of them that will continue to have coherence over long distances. For quarks however, the large mass differences means that the different mass states will lose coherence practically immediately, leading to no quark flavour oscillations (as you can tell which mass state has been produced by looking at the kinematics of the process).

    What does happen in the baryon sector due to CKM mixing is neutral meson oscillations, for example between ##K_0## (quark content ##d\bar s##) and ##\bar K_0## (##s\bar d##).
     
  21. Dec 15, 2017 #19
    OK. So I'm hearing that quarks can oscillate a little between mass generations (flavor). Do they oscillate between up and down type, or between color charge or electric charge? Thanks again.
     
  22. Dec 15, 2017 #20

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member
    2017 Award

    I do not understand how you got that from what I said. What you have is neutral meson oscillations.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Loading...