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How could 2nd and 3rd gen. quarks be possibly discovered?

  1. Apr 14, 2006 #1

    I just got into the particle physics and so I met the first problem. Scientists claim that they had discovered higher generation quarks in the colliders but: If quarks are fundamental particles, and all the matter in our universe is only based upon up and down quarks, how 2nd and 3rd generations gained mass during the collision? Since their charges are the same, the only thing that is different is actually their mass, but again how did they gain mass during collision? It would need some kind of free material to be glued to up or either down quarks :rolleyes: but since its fundamental there possibly couldn't be any additional materials to make up the quarks.

    The only thing right now I can think of, is that the super high energy could possible add more energy to the quarks, possibly enlarging their mass, but again how do they absorb energy and what determines their charge?

    Thanks for all the help,
  2. jcsd
  3. Apr 14, 2006 #2


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    I think you hit the nail right on the head with this comment, but the standard model view of the various generations is that they are different eigenstates of mass. Your same question exists in the leptons, both charged (electron, muon and tau) and neutral (neutrinos).

    Taking the -1/3 quarks "dsb", the idea is that one can split these states into the d, s and b by looking for mass eigenvectors. Now the weak force can change a -1/3 quark into a +2/3 quark "uct" by having the "dsb" quark absorb a W+ or emit a W-. But in doing this, the d s and b do not map 1-1 over to the u c and t. So it's only in the weak force that these particles are mixed.

    In QM in general, particles are only wave conditions that are eigenvectors of various measurements. In the absence of a measurement, one can obtain a mixture of different quarks. For example, if a d quark absorbs a W+, the result is not any one particular up type quark. Instead, you get a combination of all of them. To get just one, you have to make a mass measurement.

  4. Apr 15, 2006 #3
    Sorry, but I can scarcely understand this yet. Here I have some new questions, when quarks interact, they produce a strong nuclear force, or gluons, which disallows them to split. Hence, the proton or neutron as yet can't split. But for example during the interaction with W boson, wouldn't it be needed that each quark is separated and then its mass increases? Now my knowledge is a little bit tottering. I previously learned that protons are held with neutrons using a nuclear force. But since this nuclear force can be broken up during high energy collisions, and nobody was able to break up the force holding up quarks, I must conclude that quark's nuclear force is stronger that that of protons and neutrons. But again if it isn't so, and the force is the same, then the actual atom would look something like this, (not exact):

    Here I have some more questions, just make sure you remember that I have no physics background and all of them may be very stupid and dumb.
    What determines the charge of the particle, how is it chosen that for exampple this particle is to have positive charge, this neutral and so on?
    Why Z boson is useless?
    Is atomic level, as QM predicts weird, warped, carved and random, unpredictable just because we aren't able to see it. Or the randomness would still exist even if we shrink ourselves to the atomic level.
    why electrons always follow their path in pattern, and if EM force wouldn't exist, would electrons fall away from the nucleus?
    Is time and space around us warped? Is it possible that these are not the heavy objects like sun that warp the space time, but simply atoms do it. We just don't realize it because we live in a warped and carved space-time and once you leave a solar system or galaxy, time and space become smooth?

    Thanks, and looking for all the answers :)
    Last edited: Apr 15, 2006
  5. Apr 16, 2006 #4


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    As for the discovery process, it only partly comes from the big colliders. First "new" quark was the "strange" quark, needed to explain the Kaons, which were the K-mesons discovered in cosmic rays during the early fifties. And actually it was not that first a "one generation theory" was postulated and then a second and a third one; the mass of kaons was near enough to pions to postulate a symmetry "SU(3) flavour" enlarging the "SU(2) isospin" of neutrons and protons; such symmetries were interpreted in terms of quarks by some people, but just mathematically by some others. First a new quantum number (Pais Strangeness) and then a fourth quark (GIM mechanism) was postulated in order to get the right decay rate of kaons, and this was discovered years later, the "charm" quark. The corresponding boson, J\Psi, is too massive to be put in a "SU(4)" symmetry, so the people on the mathematical interpretation surrendered to the reality of the quarks as existing particles.

    So, we started with u,d,s then conjectured (GIM mechanism) c, and noticed that the right gruping was (u,d) (c,s) ... Then a mathematical argument grouped them with the generations of leptons. So the discovery of a third charged lepton, tau, was to mean the prediction of a new pair of quarks (b,d)

    The uselessness of Z0 (it does not change quark or lepton flavour) become useful when we reached the energy to produce Z0 and let them to disintegrate, because they must disintegrate to pairs of equal particle/antiparticle, as a photon must, but they even couple to neutrinos (as a photon doesn't). Thus we were able to measure that the number of generations with neutrino masses smaller thant Z0 mass is less than four and compatible with three.
    Last edited: Apr 16, 2006
  6. Apr 17, 2006 #5
    That's sort of close. Remember E=mc^2. So, if you smash particles together with enough energy, some of the time that energy will be converted into mass in the form of whatever particles are available. When you crank up your accelerator to a high enough energy to produce a new particle (b-b-bar, for instance), you get a spike in the scattering probability.

    But, it's not that the quarks in the colliding particles are gaining mass, rather, the energy of the collision is being converted into completely new particles.
  7. Apr 17, 2006 #6
    Hey, thanks for help, but
    What is an energy? and yet can it possibly exist free of the matter just energy alone without needed particles or yet energy is the part of matter just like brain is the part of human, you cannot function without brain?
    I don't know

    Thanks, and I'm again looking for some help :)
  8. Apr 17, 2006 #7


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    This is the energy density of electric and magnetic field from classical E&M. Can you point out where there is a "particle" or "matter" anywhere in this representation?


  9. Apr 17, 2006 #8
    Hey, also thank you for help

    Alright, this energy is stored in particles, if refering to the website. (Huh, I still don't know what the energy is) From that I can derive that those fields store energy in particles, but yet are those fields those that make the energy possible?

    Thanks for the website.
  10. Apr 17, 2006 #9


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    Look at the derivation of the the E and B field (which can be done in vacuum). Where are these "particle" in the formulation?

    Try not to simply spew out these things without showing exactly where in the physics all these things you are claiming.

  11. Apr 21, 2006 #10
    Alright, let it be, but do you use a concept of graviton while calculating the gravitational force? I think it would be easier to understand for me if you explain what the energy is. You know, we all are talking about energy, energy this, energy that, but what the energy really is. Thanks,

    Hey, thanks for some help.
    I know this may sound stupid and probably does, but if energy produces these particles then, how does energy know whether specific particle is to have what charge? Whether it's suppossed to be lepton or quark, and if it's fundamental, what "material" should be built of? And if quarks are produced by interference with W bosons, then How the boson knows the it only gets to interfere with quarks and leptons, and not for example with gluons, and so on? It's pretty hard to understand it for me. After reading about interferences, particles, and forces it really looks to me like our universe may work on similar way like DNA in humans, having stored all these informations on what to do where, somewhere.

    Thanks, and still looking for help :)
  12. Apr 21, 2006 #11


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    No, I don't use the concept of graviton while calculating the gravitational force. Why should I? What's wrong with the conventional way of calculation? Why would I use something that hasn't been verified, both theoretically and experimentally?

    What exactly is the problem you are having with "energy"? Do you want the classical description of it? Would it be sufficient if I point to the Lagrangian? What about the Hamiltonian in QM?

  13. Apr 21, 2006 #12
    I just don't know what it is :cry: If you can, please describe it in something I'll understand. I don't want take up your time, but if you do have some free, provide me with everything you know that fit the question "what is energy?"
  14. Apr 25, 2006 #13
    The question "what is energy" is a pretty difficult one to answer in general. In the particle collision context you're talking about there are basically two types of energy to think about: the mass of the particles and their kinetic energy.

    Let's say we have an accelerator that collides electrons and positrons, and we want to make a pair of heavy quarks, say b b-bar. The b quark has a mass of about 4 GeV, the electron a mass of about 0.5 MeV (or a factor of 8000 smaller). So, what we have to do is to accelerate the electrons so that they have a kinetic energy of at least 4 GeV each. Then, by E=mc^2 that kinetic energy can be converted into the mass of the b quarks.

    Now, it's a little more complicated than that. Why, you ask, would the energy from the electrons go into forming the quarks? The answer is that they both interact with photons. Roughly, the electron and positron annihilate to form a photon. That photon then dissintigrates into the b b-bar pair.

    How does it know to disintigrate into b quarks? It doesn't. This is where quantum mechanics comes in in a big way. There is a probability for the photon to make a b b-bar pair. There is also a probability for it to go back into an electron and a positron, or to a muon and an anti-muon, or into other types of quarks. In each collision one of these will happen at random, with a certain, calculable, probability for each. So, to make b quarks we need to collide electons and positrons a bunch of times until we get what we want.

    Hope that helps.
  15. Apr 25, 2006 #14
    Sure that helps, helps a lot. Can you also help me with different questions and explanations, in thread "Lack of understanding of quarks, energy..." That's the one I need much more and have more problems in understanding.
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