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Does the decay of the Higgs Boson create up or down quarks?

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Yes, it can. But the probability is so small that it's barely worth considering, and that's why you won't see it in most plots of Higgs branching ratios (the relative probabilities of decaying into different kinds of particles), nor mentioned in lists of what the Higgs can decay into.

Roughly, the probability of the Higgs boson decaying into a particular particle and its antiparticle is proportional to the mass of the particle squared, and since the up and down quarks are thousands of times less massive than, say, the bottom or charm quarks, the probability of $H\to u\bar{u}$ or $H\to d\bar{d}$ is on the order of a millionth of $H\to c\bar{c}$ or $H\to b\bar{b}$. Considering how rare it is to produce a Higgs boson in the first place, odds are that the decay $H\to u\bar{u}$ or $H\to d\bar{d}$ has happened maybe once or twice in the entire time the LHC has been running.

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Thanks very much. So does this mean that up and down quarks which make up protons and neutrons are more likely to have come into existence via a different path? – Tracy Oct 12 '13 at 12:47

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