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How is the quark model symmetrical and how did this lead to the discovery of t & b ? watch

    • Thread Starter

    how did the symmetry of the model lead to prediction of the top and bottom quark?

    basically, scientists 'know' (don't ask me how) that the universe is symmetrical. So, obviously, the fundamental particles are symmetrical. They had 6 leptons, therefore they must have 6 quarks. Knowing this, they experimented until they produced the bottom quark (hence proving the existence of the top quark), later, the top quark was proven through experiments.

    If this is A level physics, it's pretty much all you should know. [well, if it's Edexcel...]

    If this is university physics, this should cover it:

    The predictions of top and bottom quark came from the GIM mechanism and quark mixing via the CKM matrix. Initially the CKM matrix was proposed as only a unitary 2x2 rotation matrix mixing Up and Down quarks and Charm and Stange.

    This changed when CP violating decays were observed in neutral Kaon decay channels. The neutral kaon primarily decays by 1 of 2 decay channels, of different lifetimes, called  k_l and  k_s for long and short. These also have opposite CP eigenvalues. It was found that a beam having had all  k_s component being removed could still produce decay products with the 'wrong' CP eigenvalue, meaning that CP violation had occurred.

    To explain this, it was proposed that the CKM matrix should actually be a 3x3 unitary rotation matrix. This is because a 3x3 rotation matrix contains at least one non-trivial complex component, which under the CP operation reverses sign and thus provides a theoretical basis for the CP violation seen in the neutral Kaon channel. The problem was that for this to work, 2 more particles were needed. Looking at the 3 families present in the leptons, it wasn't too much of a stretch to propose the same in the quarks and indeed in 1977 the B quark was found.

    So to answer the question directly, it was the observation of the violation of CP symmetry in experiments (previously assumed to be absolutely obeyed in the standard model) that led to the theorising of the T and B, which prompted experimentalists to look for it.
    • Thread Starter

    ok...you guys are amazing.....thank you!
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