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5 quarks?

  1. May 12, 2004 #1
    Apparently, a subatomic particle with 5 quarks has been "discovered"... :wink: (not quite confirmed)


    http://physicsweb.org/article/news/7/7/1

    How do scientists determine the number of quarks in a particle?
    Is it true that a subatomic particle must have at least 3 quarks? why? how is it determined? what is the maximum number of quarks that can be in a subatomic particle? :confused:

    and here is another article, the author claims to be able to explain that there are no quarks... :eek: :surprise:

    http://www.subatomicparticles.com/
     
    Last edited: May 12, 2004
  2. jcsd
  3. May 13, 2004 #2

    chroot

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    Yes, pentaquarks have been made recently.

    There are many particles composed of only two quarks: they are called "mesons."

    The number of quarks that can be combined in one particle is determined by colour. A particle must be overall colour-neutral. There are three colors of quarks: red, green, and blue. (Not to be confused with real colors -- these are just the names chosen by physicists to represent the three types). There are also three anti-colors: anti-red, anti-green, and anti-blue.

    You can combine a red and an anti-red quark (or green and anti-green, etc.) and get a particle that is overall colour-neutral. That's allowed. Two-quark particles are allowed.

    You can combine three each of red, green, and blue quarks (or three each of anti-red, anti-green, and anti-blue), and also get a colour-neutral particle. (That's the reason the particles are compared to colors in the first place -- because of the similarity with the way red, green, and blue light combine to form white light.) Thus, three quark particles are allowed.

    You can combine a meson (a two-quark particle) with a baryon (a three-quark particle), and create a five quark particle, and that's allowed, too.

    You could go on to create particles with any number of quarks you want.

    - Warren
     
  4. May 13, 2004 #3

    jcsd

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    There is strong evidence that a tetraquark, a particle with 4 quarks, was also created last year, infact as Chroot sdays you can (in theory) create particles made up of any number of quarks with the exception of one quark (as a quark by itself can never be colour-neutral).

    Particles that are made of quarks are known as hadrons and are divided into two catergories: baryons and mesons. Baryons are made up of three quarks (including protons and neutrons) and mesons are made up of two quarks (including pions and kaons). All quarks have a spin of 1/2 (h-bar). The total spin of a hadron will be the vector sum of the spin of it's component quarks, so this means that mesons will always have an integer spin and therefore be in the class of particles known as bosons (whose non-hadronic memebers include photons, gluons and the theoretical graviton) and baryons will always have a half-interger spin and therefore be in the class of particles known as fermions (whose non-hadronic members include electrons, neutrinos and muons and).

    So finally to my point: how do you classify the pentaquark? You should be able to see that the pentaquark has a half-interger spin and therefore is a fermion. This means it fits most comfortably into the baryon family (and more importantly being composed of 3 quarks and one antiquark it has a baryon number of 1), of course memebrs of the baryon family usually have three quarks so it is quite often given it's own family: the exotic baryons.
     
  5. May 13, 2004 #4
    Are K-mesons (kaons) radioactive (is that why they're referred to as "high energy")?
    Do the high energy particle collisions needed to "make" a kaon have to incorperate mesons?

    How are pi mesons formed? Are pions a category for other particles too?
     
  6. May 14, 2004 #5

    jcsd

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    Kaons are radioactive in the sense that they decay (via the weak force), when a particle is said to be 'high energy' it usually means that it has a high velocity. Neutral kaons can decay into pions. In order "to make" a kaon you don't necessarily need mesons.

    There are many ways of forming pions, for example electron-positron anhilation and kaon decay. There are three distinct pions, one with postive charge, one with negative charge and one with neutral charge.
     
  7. May 14, 2004 #6
    How do virtual photons into the picture in an antiparticle-particle annihelation?
     
  8. May 14, 2004 #7

    jcsd

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    They don't fit directly into anhilation, but for example an electron and positron being attracted would be mediated by a virtual photon.

    edited goto add i've just had a look at the Feynman diagram for proton-antiproton production in electron-positron annihilation and it does involve a virtual photon.
     
    Last edited: May 14, 2004
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