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Unformatted text preview: 1409 Chapter 41 Elementary Particles and the Beginning of the Universe Conceptual Problems 1 Similarities Differences Baryons and mesons are hadrons, i.e., they participate in the strong interaction. Both are composed of quarks. Baryons consist of three quarks and are fermions. Mesons consist of two quarks and are bosons. Baryons have baryon number +1 or 1. Mesons have baryon number 0. 2 Determine the Concept The muon is a lepton. It is a spin particle and is a fermion. It does not participate in strong interactions. It appears to be an elementary particle like the electron. The pion is a meson. Its spin is 0 and it is a boson. It does participate in strong interactions and is composed of quarks. *3 Determine the Concept A decay process involving the strong interaction has a very short lifetime ( 10 23 s), whereas decay processes that proceed via the weak interaction have lifetimes of order 10 10 s. 4 ( a ) True ( b ) False. There are two kinds of hadronsbaryons, which have spin 2 1 (or , , 2 5 2 3 and so on), and mesons, which have zero or integral spin. 5 False. Mesons have zero or integral spins. 6 Determine the Concept A meson has 2 quarks, a baryon has 3 quarks. 7 Determine the Concept No; from Table 412 it is evident that any quarkantiquark combination always results in an integral or zero charge. Chapter 41 1410 8 ( a ) False. Leptons are not made up of quarks. ( b ) True ( c ) False. Electrons are leptons and leptons interact via the weak interaction. ( d ) True ( e ) True *9 Determine the Concept No. Such a reaction is impossible. A proton requires three quarks. Three quarks are not available because a pion is made of a quark and an antiquark and the antiproton consists of three antiquarks. Estimation and Approximation 10 Picture the Problem Assuming that the lifetime of a proton is 10 32 y, one proton out of every 10 32 protons should decay every year on average. Hence, we can estimate the expected time between protondecays that occur in the water of a filled Olympicsize swimming pool by determining the number of protons N in the pool and dividing 10 32 y by this number. The mean time between disintegrations is the ratio of the lifetime of the protons to the number of protons N in the pool: N t y 10 32 mean = (1) The number of protons N in the pool is related to the mass of water in the pool M water , the molar mass of water m molar, water , and the number of protons per molecule n : water molar, A water m nN M N = Solve for N to obtain: water molar, water A m M nN N = Because the mass of the water is the product of its density and the volume of the pool: water molar, pool water A m V nN N = Elementary Particles and the Beginning of the Universe 1411 Substituting for N in equation (1) yields: ( ) pool water A water molar, 32 water molar, pool water A 32 mean y 10 y 10 V nN m m V nN t = = Because each molecule of water has 10 protons: molecule protons 10 =...
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 Spring '07
 MACKAY

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