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There are particles called bottom mesons or $B^-$ mesons. One of them is the $B^-$ meson, which has a single negative charge; its baryon number is zero, as are its strangeness, charm, and topness. It has a bottomness of −1 . What is its quark configuration?
$\textrm{b}\overline{\textrm{u}}$
Solution Video

# OpenStax College Physics for AP® Courses Solution, Chapter 33, Problem 40 (Problems & Exercises) (1:40)

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This is College Physics Answers with Shaun Dychko. We are told that the B minus meson has a negative 1 charge, a bottomness of negative 1 and a baryon number, strangeness, charm and topness all of 0 and being a meson means it can have only two quarks in it and the question is what are those two quarks? So to have a bottomness of negative 1, it will certainly need to have a bottom regular matter quark and so that's why we wrote b here and then we need to add some other quark that will not introduce any strangeness, charm, bottomness or topness to the mix and so that precludes everything up until this up and down options and now we need to look at baryon numbers say... if we want a baryon number of 0, we need something that will offset the positive one-third baryon number from the bottom quark and so we will need a negative one-third baryon number from these particles and that means it has to be either an anti-up or an anti-down quark based on that and then we need to also consider the fact that it has to have a negative 1 charge and we have negative one-third in the bottom quark and so we need to further negative two-thirds to turn that into a total of negative 1 and so that means it has to be the up anti-quark in order to fit the bill with a negative 1 charge and a bottomness of negative 1 and all these other things being 0.